Conversión de tipos en .NET FrameworkType Conversion in the .NET Framework

• 03/30/2017
• Tiempo de lectura: 21 minutos
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Cada valor tiene un tipo asociado, que define atributos como la cantidad de espacio asignado al valor, el intervalo de valores posibles que puede tener y los miembros que ofrece.Every value has an associated type, which defines attributes such as the amount of space allocated to the value, the range of possible values it can have, and the members that it makes available. Muchos valores se pueden expresar como más de un tipo.Many values can be expressed as more than one type. Por ejemplo, el valor 4 se puede expresar como un entero o como un valor de punto flotante.For example, the value 4 can be expressed as an integer or a floating-point value. La conversión de tipo crea un valor en un nuevo tipo que es equivalente al valor de un tipo antiguo, pero no conserva necesariamente la identidad (o valor exacto) del objeto original.Type conversion creates a value in a new type that is equivalent to the value of an old type, but does not necessarily preserve the identity (or exact value) of the original object.

.NET Framework admite automáticamente las conversiones siguientes:The .NET Framework automatically supports the following conversions:

• Conversión de una clase derivada a una clase base.Conversion from a derived class to a base class. Esto significa, por ejemplo, que una instancia de cualquier clase o estructura se puede convertir en una instancia de tipo Object.This means, for example, that an instance of any class or structure can be converted to an Object instance. Esta conversión no requiere un operador de conversión.This conversion does not require a casting or conversion operator.

• Conversión de una clase base a la clase derivada original.Conversion from a base class back to the original derived class. En C#, esta conversión requiere un operador de conversión.In C#, this conversion requires a casting operator. En Visual Basic, requiere el operador CType si Option Strict está activado.In Visual Basic, it requires the CType operator if Option Strict is on.

• Conversión de un tipo que implementa una interfaz a un objeto de interfaz que representa esa interfaz.Conversion from a type that implements an interface to an interface object that represents that interface. Esta conversión no requiere un operador de conversión.This conversion does not require a casting or conversion operator.

• Conversión de un objeto de interfaz al tipo original que implementa esa interfaz.Conversion from an interface object back to the original type that implements that interface. En C#, esta conversión requiere un operador de conversión.In C#, this conversion requires a casting operator. En Visual Basic, requiere el operador CType si Option Strict está activado.In Visual Basic, it requires the CType operator if Option Strict is on.

Además de estas conversiones automáticas, .NET Framework proporciona varias características que admiten la conversión de tipos personalizada.In addition to these automatic conversions, the .NET Framework provides several features that support custom type conversion. Entre ellas se incluyen las siguientes:These include the following:

• El operador Implicit, que define las conversiones de ampliación disponibles entre los tipos.The Implicit operator, which defines the available widening conversions between types. Para obtener más información, consulte la sección Conversión implícita con el operador Implicit.For more information, see the Implicit Conversion with the Implicit Operator section.

• El operador Explicit, que define las conversiones de restricción disponibles entre los tipos.The Explicit operator, which defines the available narrowing conversions between types. Para obtener más información, consulte la sección Conversión explícita con el operador Explicit.For more information, see the Explicit Conversion with the Explicit Operator section.

• La interfaz IConvertible, que define las conversiones en cada uno de los tipos de datos base de .NET Framework.The IConvertible interface, which defines conversions to each of the base .NET Framework data types. Para obtener más información, vea Interfaz IConvertible.For more information, see The IConvertible Interface section.

• La clase Convert, que proporciona un conjunto de métodos que implementan los métodos de la interfaz IConvertible.The Convert class, which provides a set of methods that implement the methods in the IConvertible interface. Para obtener más información, vea la sección Clase Convert.For more information, see The Convert Class section.

• La clase TypeConverter, que es una clase base que se puede extender para admitir la conversión de un tipo concreto en cualquier otro tipo.The TypeConverter class, which is a base class that can be extended to support the conversion of a specified type to any other type. Para obtener más información, vea Clase TypeConverter.For more information, see The TypeConverter Class section.

Conversión implícita con el operador ImplicitImplicit Conversion with the Implicit Operator

Las conversiones de ampliación implican la creación de un nuevo valor a partir del valor de un tipo existente que tiene un intervalo más restrictivo o una lista de miembros más restringida que el tipo de destino.Widening conversions involve the creation of a new value from the value of an existing type that has either a more restrictive range or a more restricted member list than the target type. Las conversión de ampliación no pueden producir ninguna pérdida de datos (aunque pueden producir una pérdida de precisión).Widening conversions cannot result in data loss (although they may result in a loss of precision). Puesto que no se pueden perder datos, los compiladores pueden administrar la conversión de manera implícita o transparente, sin que sea necesario el uso de un método de conversión explícito o de un operador de conversión.Because data cannot be lost, compilers can handle the conversion implicitly or transparently, without requiring the use of an explicit conversion method or a casting operator.

Por ejemplo, el tipo Decimal admite conversiones implícitas a partir de valores Byte, Char, Int16, Int32, Int64, SByte, UInt16, UInt32 y UInt64.For example, the Decimal type supports implicit conversions from Byte, Char, Int16, Int32, Int64, SByte, UInt16, UInt32, and UInt64 values. En el ejemplo siguiente se muestran algunas de estas conversiones implícitas al asignar valores a una variable Decimal.The following example illustrates some of these implicit conversions in assigning values to a Decimal variable.

byte byteValue = 16;
short shortValue = -1024;
int intValue = -1034000;
long longValue = 1152921504606846976;
ulong ulongValue = UInt64.MaxValue;

decimal decimalValue;

decimalValue = byteValue;
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  byteValue.GetType().Name, decimalValue);

decimalValue = shortValue;
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  shortValue.GetType().Name, decimalValue);

decimalValue = intValue;
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  intValue.GetType().Name, decimalValue);

decimalValue = longValue;
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  longValue.GetType().Name, decimalValue);

decimalValue = ulongValue;
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  longValue.GetType().Name, decimalValue);
// The example displays the following output:
//    After assigning a Byte value, the Decimal value is 16.
//    After assigning a Int16 value, the Decimal value is -1024.
//    After assigning a Int32 value, the Decimal value is -1034000.
//    After assigning a Int64 value, the Decimal value is 1152921504606846976.
//    After assigning a Int64 value, the Decimal value is 18446744073709551615.

Dim byteValue As Byte = 16
Dim shortValue As Short = -1024
Dim intValue As Integer = -1034000
Dim longValue As Long = CLng(1024^6)
Dim ulongValue As ULong = ULong.MaxValue

Dim decimalValue As Decimal

decimalValue = byteValue
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  byteValue.GetType().Name, decimalValue) 
                         
decimalValue = shortValue
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  shortValue.GetType().Name, decimalValue) 

decimalValue = intValue
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  intValue.GetType().Name, decimalValue) 

decimalValue = longValue
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  longValue.GetType().Name, decimalValue) 
                  
decimalValue = ulongValue
Console.WriteLine("After assigning a {0} value, the Decimal value is {1}.",
                  longValue.GetType().Name, decimalValue) 
' The example displays the following output:
'    After assigning a Byte value, the Decimal value is 16.
'    After assigning a Int16 value, the Decimal value is -1024.
'    After assigning a Int32 value, the Decimal value is -1034000.
'    After assigning a Int64 value, the Decimal value is 1152921504606846976.
'    After assigning a Int64 value, the Decimal value is 18446744073709551615.

Si un compilador de un lenguaje determinado admite operadores personalizados, también puede definir conversiones implícitas en sus propios tipos personalizados.If a particular language compiler supports custom operators, you can also define implicit conversions in your own custom types. En el ejemplo siguiente se proporciona una implementación parcial de un tipo de datos de byte con signo denominado ByteWithSign que usa la representación de signo y magnitud.The following example provides a partial implementation of a signed byte data type named ByteWithSign that uses sign-and-magnitude representation. Admite la conversión implícita de valores Byte y SByte a valores ByteWithSign.It supports implicit conversion of Byte and SByte values to ByteWithSign values.

public struct ByteWithSign
{
   private SByte signValue;
   private Byte value;

   public static implicit operator ByteWithSign(SByte value)
   {
      ByteWithSign newValue;
      newValue.signValue = (SByte) Math.Sign(value);
      newValue.value = (byte) Math.Abs(value);
      return newValue;
   }

   public static implicit operator ByteWithSign(Byte value)
   {
      ByteWithSign  newValue;
      newValue.signValue = 1;
      newValue.value = value;
      return newValue;
   }

   public override string ToString()
   {
      return (signValue * value).ToString();
   }
}

Public Structure ByteWithSign
   Private signValue As SByte 
   Private value As Byte
   
   Public Overloads Shared Widening Operator CType(value As SByte) As ByteWithSign
      Dim newValue As ByteWithSign
      newValue.signValue = CSByte(Math.Sign(value))
      newValue.value = CByte(Math.Abs(value))
      Return newValue
   End Operator  
   
   Public Overloads Shared Widening Operator CType(value As Byte) As ByteWithSign
      Dim NewValue As ByteWithSign
      newValue.signValue = 1
      newValue.value = value
      Return newValue
   End Operator
   
   Public Overrides Function ToString() As String 
      Return (signValue * value).ToString()
   End Function
End Structure

A continuación, el código de cliente puede declarar una variable ByteWithSign y asignarle valores Byte y SByte sin realizar ninguna conversión explícita ni emplear ningún operador de conversión, como se muestra en el ejemplo siguiente.Client code can then declare a ByteWithSign variable and assign it Byte and SByte values without performing any explicit conversions or using any casting operators, as the following example shows.

SByte sbyteValue = -120;
ByteWithSign value = sbyteValue;
Console.WriteLine(value);
value = Byte.MaxValue;
Console.WriteLine(value);
// The example displays the following output:
//       -120
//       255

Dim sbyteValue As SByte = -120
Dim value As ByteWithSign = sbyteValue
Console.WriteLine(value.ToString()) 
value = Byte.MaxValue
Console.WriteLine(value.ToString()) 
' The example displays the following output:
'       -120
'       255

Conversión explícita con el operador ExplicitExplicit Conversion with the Explicit Operator

Las conversiones de restricción implican la creación de un nuevo valor a partir del valor de un tipo existente que tiene un intervalo mayor o una lista de miembros mayor que el tipo de destino.Narrowing conversions involve the creation of a new value from the value of an existing type that has either a greater range or a larger member list than the target type. Puesto que una conversión de restricción puede producir una pérdida de datos, los compiladores suelen necesitar que la conversión se haga explícita a través de una llamada a un método de conversión o a un operador de conversión.Because a narrowing conversion can result in a loss of data, compilers often require that the conversion be made explicit through a call to a conversion method or a casting operator. Es decir, la conversión se debe administrar explícitamente en el código de desarrollo.That is, the conversion must be handled explicitly in developer code.

Por ejemplo, los tipos de datos UInt32, Int64 y UInt64 tienen intervalos que superan el del tipo de datos Int32, como se muestra en la tabla siguiente.For example, the UInt32, Int64, and UInt64 data types have ranges that exceed that the Int32 data type, as the following table shows.

Para administrar estas conversiones de restricción, .NET Framework permite que los tipos definan un operador Explicit.To handle such narrowing conversions, the .NET Framework allows types to define an Explicit operator. A continuación, los compiladores de lenguaje individuales pueden implementar este operador usando su propia sintaxis o se puede llamar a un miembro de la clase Convert para realizar la conversión.Individual language compilers can then implement this operator using their own syntax, or a member of the Convert class can be called to perform the conversion. (Para obtener más información sobre la clase Convert, vea Clase Convert más adelante en este tema). En el ejemplo siguiente se muestra el uso de las características de lenguaje para administrar la conversión explícita de estos valores enteros, que potencialmente están fuera del intervalo, a valores Int32.(For more information about the Convert class, see The Convert Class later in this topic.) The following example illustrates the use of language features to handle the explicit conversion of these potentially out-of-range integer values to Int32 values.

long number1 = int.MaxValue + 20L;
uint number2 = int.MaxValue - 1000;
ulong number3 = int.MaxValue;

int intNumber;

try {
   intNumber = checked((int) number1);
   Console.WriteLine("After assigning a {0} value, the Integer value is {1}.",
                     number1.GetType().Name, intNumber);
}
catch (OverflowException) {
   if (number1 > int.MaxValue)
      Console.WriteLine("Conversion failed: {0} exceeds {1}.",
                        number1, int.MaxValue);
   else
      Console.WriteLine("Conversion failed: {0} is less than {1}.",
                        number1, int.MinValue);
}

try {
   intNumber = checked((int) number2);
   Console.WriteLine("After assigning a {0} value, the Integer value is {1}.",
                     number2.GetType().Name, intNumber);
}
catch (OverflowException) {
   Console.WriteLine("Conversion failed: {0} exceeds {1}.",
                     number2, int.MaxValue);
}

try {
   intNumber = checked((int) number3);
   Console.WriteLine("After assigning a {0} value, the Integer value is {1}.",
                     number3.GetType().Name, intNumber);
}
catch (OverflowException) {
   Console.WriteLine("Conversion failed: {0} exceeds {1}.",
                     number1, int.MaxValue);
}

// The example displays the following output:
//    Conversion failed: 2147483667 exceeds 2147483647.
//    After assigning a UInt32 value, the Integer value is 2147482647.
//    After assigning a UInt64 value, the Integer value is 2147483647.

Dim number1 As Long = Integer.MaxValue + 20L
Dim number2 As UInteger = Integer.MaxValue - 1000
Dim number3 As ULong = Integer.MaxValue

Dim intNumber As Integer

Try
   intNumber = CInt(number1)
   Console.WriteLine("After assigning a {0} value, the Integer value is {1}.", 
                       number1.GetType().Name, intNumber)
Catch e As OverflowException
   If number1 > Integer.MaxValue Then
      Console.WriteLine("Conversion failed: {0} exceeds {1}.", 
                                        number1, Integer.MaxValue)
   Else
      Console.WriteLine("Conversion failed: {0} is less than {1}.\n", 
                                        number1, Integer.MinValue)
   End If
End Try

Try
   intNumber = CInt(number2)
   Console.WriteLine("After assigning a {0} value, the Integer value is {1}.", 
                       number2.GetType().Name, intNumber)
Catch e As OverflowException
   Console.WriteLine("Conversion failed: {0} exceeds {1}.", 
                                     number2, Integer.MaxValue)
End Try

Try
   intNumber = CInt(number3)
   Console.WriteLine("After assigning a {0} value, the Integer value is {1}.", 
                       number3.GetType().Name, intNumber)
Catch e As OverflowException
   Console.WriteLine("Conversion failed: {0} exceeds {1}.",
                                     number1, Integer.MaxValue)
End Try
' The example displays the following output:
'    Conversion failed: 2147483667 exceeds 2147483647.
'    After assigning a UInt32 value, the Integer value is 2147482647.
'    After assigning a UInt64 value, the Integer value is 2147483647.

Las conversiones explícitas pueden producir resultados diferentes en los distintos lenguajes y estos resultados pueden diferir del valor devuelto por el método Convert correspondiente.Explicit conversions can produce different results in different languages, and these results can differ from the value returned by the corresponding Convert method. Por ejemplo, si el valor Double 12.63251 se convierte en Int32, el método CInt de Visual Basic y el método Convert.ToInt32(Double) de .NET Framework redondean el valor Double para devolver un valor de 13, pero el operador (int) de C# trunca Double para devolver un valor de 12.For example, if the Double value 12.63251 is converted to an Int32, both the Visual Basic CInt method and the .NET Framework Convert.ToInt32(Double) method round the Double to return a value of 13, but the C# (int) operator truncates the Double to return a value of 12. De manera similar, el operador (int) de C# no admite la conversión de booleano a entero, pero el método CInt de Visual Basic convierte un valor de true en -1.Similarly, the C# (int) operator does not support Boolean-to-integer conversion, but the Visual Basic CInt method converts a value of true to -1. Por otra parte, el método Convert.ToInt32(Boolean) convierte un valor de true en 1.On the other hand, the Convert.ToInt32(Boolean) method converts a value of true to 1.

La mayoría de los compiladores permiten realizar conversiones explícitas de manera comprobada o no comprobada.Most compilers allow explicit conversions to be performed in a checked or unchecked manner. Cuando se realiza una conversión comprobada, se produce una excepción OverflowException si el valor del tipo que se va a convertir está fuera del intervalo del tipo de destino.When a checked conversion is performed, an OverflowException is thrown when the value of the type to be converted is outside the range of the target type. Si se realiza una conversión no comprobada en las mismas condiciones, es posible que la conversión no produzca una excepción, pero no se podrá determinar con exactitud cuál será el comportamiento y se puede obtener como resultado un valor incorrecto.When an unchecked conversion is performed under the same conditions, the conversion might not throw an exception, but the exact behavior becomes undefined and an incorrect value might result.

En el siguiente ejemplo de C# se usan las palabras clave checked y unchecked para mostrar la diferencia de comportamiento cuando un valor que está fuera del intervalo de Byte se convierte en Byte.The following C# example uses the checked and unchecked keywords to illustrate the difference in behavior when a value outside the range of a Byte is converted to a Byte. La conversión comprobada produce una excepción, pero la conversión no comprobada asigna Byte.MaxValue a la variable Byte.The checked conversion throws an exception, but the unchecked conversion assigns Byte.MaxValue to the Byte variable.

int largeValue = Int32.MaxValue;
byte newValue;

try {
   newValue = unchecked((byte) largeValue);
   Console.WriteLine("Converted the {0} value {1} to the {2} value {3}.",
                     largeValue.GetType().Name, largeValue,
                     newValue.GetType().Name, newValue);
}
catch (OverflowException) {
   Console.WriteLine("{0} is outside the range of the Byte data type.",
                     largeValue);
}

try {
   newValue = checked((byte) largeValue);
   Console.WriteLine("Converted the {0} value {1} to the {2} value {3}.",
                     largeValue.GetType().Name, largeValue,
                     newValue.GetType().Name, newValue);
}
catch (OverflowException) {
   Console.WriteLine("{0} is outside the range of the Byte data type.",
                     largeValue);
}
// The example displays the following output:
//    Converted the Int32 value 2147483647 to the Byte value 255.
//    2147483647 is outside the range of the Byte data type.

Si un compilador de un lenguaje determinado admite operadores sobrecargados personalizados, también puede definir conversiones explícitas en sus propios tipos personalizados.If a particular language compiler supports custom overloaded operators, you can also define explicit conversions in your own custom types. En el ejemplo siguiente se proporciona una implementación parcial de un tipo de datos de byte con signo denominado ByteWithSign que usa la representación de signo y magnitud.The following example provides a partial implementation of a signed byte data type named ByteWithSign that uses sign-and-magnitude representation. Admite la conversión explícita de valores Int32 y UInt32 a valores ByteWithSign.It supports explicit conversion of Int32 and UInt32 values to ByteWithSign values.

public struct ByteWithSign
{
   private SByte signValue;
   private Byte value;

   private const byte MaxValue = byte.MaxValue;
   private const int MinValue = -1 * byte.MaxValue;

   public static explicit operator ByteWithSign(int value)
   {
      // Check for overflow.
      if (value > ByteWithSign.MaxValue || value < ByteWithSign.MinValue)
         throw new OverflowException(String.Format("'{0}' is out of range of the ByteWithSign data type.",
                                                   value));

      ByteWithSign newValue;
      newValue.signValue = (SByte) Math.Sign(value);
      newValue.value = (byte) Math.Abs(value);
      return newValue;
   }

   public static explicit operator ByteWithSign(uint value)
   {
      if (value > ByteWithSign.MaxValue)
         throw new OverflowException(String.Format("'{0}' is out of range of the ByteWithSign data type.",
                                                   value));

      ByteWithSign newValue;
      newValue.signValue = 1;
      newValue.value = (byte) value;
      return newValue;
   }

   public override string ToString()
   {
      return (signValue * value).ToString();
   }
}

Public Structure ByteWithSign
   Private signValue As SByte 
   Private value As Byte
   
   Private Const MaxValue As Byte = Byte.MaxValue
   Private Const MinValue As Integer = -1 * Byte.MaxValue

   Public Overloads Shared Narrowing Operator CType(value As Integer) As ByteWithSign
      ' Check for overflow.
      If value > ByteWithSign.MaxValue Or value < ByteWithSign.MinValue Then
         Throw New OverflowException(String.Format("'{0}' is out of range of the ByteWithSign data type.", value))
      End If
      
      Dim newValue As ByteWithSign
      
      newValue.signValue = CSByte(Math.Sign(value))
      newValue.value = CByte(Math.Abs(value))
      Return newValue
   End Operator
   
   Public Overloads Shared Narrowing Operator CType(value As UInteger) As ByteWithSign
      If value > ByteWithSign.MaxValue Then 
         Throw New OverflowException(String.Format("'{0}' is out of range of the ByteWithSign data type.", value))
      End If
       
      Dim NewValue As ByteWithSign

      newValue.signValue = 1
      newValue.value = CByte(value)
      Return newValue
   End Operator
   
   Public Overrides Function ToString() As String 
      Return (signValue * value).ToString()
   End Function
End Structure

A continuación, el código de cliente puede declarar una variable ByteWithSign y asignarle valores de tipo Int32 y UInt32 si las asignaciones incluyen un operador de conversión o un método de conversión, como se muestra en el ejemplo siguiente.Client code can then declare a ByteWithSign variable and assign it Int32 and UInt32 values if the assignments include a casting operator or a conversion method, as the following example shows.

ByteWithSign value;

try {
   int intValue = -120;
   value = (ByteWithSign) intValue;
   Console.WriteLine(value);
}
catch (OverflowException e) {
   Console.WriteLine(e.Message);
}

try {
   uint uintValue = 1024;
   value = (ByteWithSign) uintValue;
   Console.WriteLine(value);
}
catch (OverflowException e) {
    Console.WriteLine(e.Message);
}
// The example displays the following output:
//       -120
//       '1024' is out of range of the ByteWithSign data type.

Dim value As ByteWithSign
 
Try  
   Dim intValue As Integer = -120
   value = CType(intValue, ByteWithSign)
   Console.WriteLine(value) 
Catch e As OverflowException
   Console.WriteLine(e.Message)
End Try

Try
   Dim uintValue As UInteger = 1024
   value = CType(uintValue, ByteWithSign)
   Console.WriteLine(value) 
Catch e As OverflowException
   Console.WriteLine(e.Message)
End Try
' The example displays the following output:
'       -120
'       '1024' is out of range of the ByteWithSign data type.

La interfaz IConvertibleThe IConvertible Interface

Para admitir la conversión de cualquier tipo en un tipo base de Common Language Runtime, .NET Framework proporciona la interfaz IConvertible.To support the conversion of any type to a common language runtime base type, the .NET Framework provides the IConvertible interface. El tipo que se está implementando debe proporcionar lo siguiente:The implementing type is required to provide the following:

• Un método que devuelva el objeto TypeCode del tipo que se está implementando.A method that returns the TypeCode of the implementing type.

• Métodos para convertir el tipo que se está implementando en cada uno de los tipos base de Common Language Runtime (Boolean, Byte, DateTime, Decimal, Double, etc.).Methods to convert the implementing type to each common language runtime base type (Boolean, Byte, DateTime, Decimal, Double, and so on).

• Un método de conversión generalizado para convertir una instancia del tipo que se está implementando en otro tipo concreto.A generalized conversion method to convert an instance of the implementing type to another specified type. Las conversiones que no se admiten deben iniciar una excepción InvalidCastException.Conversions that are not supported should throw an InvalidCastException.

Cada uno de los tipos base de Common Language Runtime (es decir, Boolean, Byte, Char, DateTime, Decimal, Double, Int16, Int32, Int64, SByte, Single, String, UInt16, UInt32y UInt64), así como los tipos DBNull y Enum, implementan la interfaz IConvertible.Each common language runtime base type (that is, the Boolean, Byte, Char, DateTime, Decimal, Double, Int16, Int32, Int64, SByte, Single, String, UInt16, UInt32, and UInt64), as well as the DBNull and Enum types, implement the IConvertible interface. Sin embargo, se trata de implementaciones de interfaz explícitas; solo se puede llamar al método de conversión mediante una variable de la interfaz IConvertible, como se muestra en el ejemplo siguiente.However, these are explicit interface implementations; the conversion method can be called only through an IConvertible interface variable, as the following example shows. Este ejemplo convierte un valor Int32 en su valor Char equivalente.This example converts an Int32 value to its equivalent Char value.

int codePoint = 1067;
IConvertible iConv = codePoint;
char ch = iConv.ToChar(null);
Console.WriteLine("Converted {0} to {1}.", codePoint, ch);

Dim codePoint As Integer = 1067
Dim iConv As IConvertible = codePoint
Dim ch As Char = iConv.ToChar(Nothing)
Console.WriteLine("Converted {0} to {1}.", codePoint, ch)

El requisito de llamar al método de conversión en su interfaz, en lugar de en el tipo que se está implementando, hace que las implementaciones de interfaz explícitas resulten relativamente costosas.The requirement to call the conversion method on its interface rather than on the implementing type makes explicit interface implementations relatively expensive. En su lugar, se recomienda llamar al miembro adecuado de la clase Convert para convertir entre los tipos base de Common Language Runtime.Instead, we recommend that you call the appropriate member of the Convert class to convert between common language runtime base types. Para obtener más información, consulte la próxima sección, Clase Convert.For more information, see the next section, The Convert Class.

En su mayor parte, la interfaz IConvertible está diseñada para admitir la conversión entre los tipos base de .NET Framework.For the most part, the IConvertible interface is designed to support conversion between the base types in the .NET Framework. Sin embargo, la interfaz también puede implementarse por un tipo personalizado con el fin de admitir la conversión de ese tipo a otros tipos personalizados.However, the interface can also be implemented by a custom type to support conversion of that type to other custom types. Para obtener más información, consulte la sección Conversiones personalizadas con el método ChangeType más adelante en este tema.For more information, see the section Custom Conversions with the ChangeType Method later in this topic.

Clase ConvertThe Convert Class

Aunque se puede llamar a la implementación de la interfaz IConvertible de cada tipo base para realizar una conversión de tipo, llamar a los métodos de la clase System.Convert es la manera recomendada de convertir de un tipo base en otro de una manera independiente del lenguaje.Although each base type's IConvertible interface implementation can be called to perform a type conversion, calling the methods of the System.Convert class is the recommended language-neutral way to convert from one base type to another. Además, se puede usar el método Convert.ChangeType(Object, Type, IFormatProvider) para convertir de un tipo personalizado concreto a otro tipo.In addition, the Convert.ChangeType(Object, Type, IFormatProvider) method can be used to convert from a specified custom type to another type.

Conversiones entre los tipos baseConversions Between Base Types

La clase Convert proporciona una manera independiente del lenguaje de realizar conversiones entre los tipos base y está disponible para todos los lenguajes cuyo destino es Common Language Runtime.The Convert class provides a language-neutral way to perform conversions between base types and is available to all languages that target the common language runtime. Ofrece un conjunto completo de métodos tanto para conversiones de ampliación como de restricción e inicia una excepción InvalidCastException para las conversiones que no se admiten (como la conversión de un valor DateTime a un valor entero).It provides a complete set of methods for both widening and narrowing conversions, and throws an InvalidCastException for conversions that are not supported (such as the conversion of a DateTime value to an integer value). Las conversiones de restricción se realizan en un contexto comprobado y se inicia una excepción OverflowException si se produce un error en la conversión.Narrowing conversions are performed in a checked context, and an OverflowException is thrown if the conversion fails.

En el ejemplo siguiente se muestra el uso de la clase System.Convert para realizar varias conversiones de restricción y ampliación entre los tipos base de .NET Framework.The following example illustrates the use of the System.Convert class to perform several widening and narrowing conversions between .NET Framework base types.

// Convert an Int32 value to a Decimal (a widening conversion).
int integralValue = 12534;
decimal decimalValue = Convert.ToDecimal(integralValue);
Console.WriteLine("Converted the {0} value {1} to " +
                                  "the {2} value {3:N2}.",
                                  integralValue.GetType().Name,
                                  integralValue,
                                  decimalValue.GetType().Name,
                                  decimalValue);
// Convert a Byte value to an Int32 value (a widening conversion).
byte byteValue = Byte.MaxValue;
int integralValue2 = Convert.ToInt32(byteValue);
Console.WriteLine("Converted the {0} value {1} to " +
                                  "the {2} value {3:G}.",
                                  byteValue.GetType().Name,
                                  byteValue,
                                  integralValue2.GetType().Name,
                                  integralValue2);

// Convert a Double value to an Int32 value (a narrowing conversion).
double doubleValue = 16.32513e12;
try {
   long longValue = Convert.ToInt64(doubleValue);
   Console.WriteLine("Converted the {0} value {1:E} to " +
                                     "the {2} value {3:N0}.",
                                     doubleValue.GetType().Name,
                                     doubleValue,
                                     longValue.GetType().Name,
                                     longValue);
}
catch (OverflowException) {
   Console.WriteLine("Unable to convert the {0:E} value {1}.",
                                     doubleValue.GetType().Name, doubleValue);
}

// Convert a signed byte to a byte (a narrowing conversion).
sbyte sbyteValue = -16;
try {
   byte byteValue2 = Convert.ToByte(sbyteValue);
   Console.WriteLine("Converted the {0} value {1} to " +
                                     "the {2} value {3:G}.",
                                     sbyteValue.GetType().Name,
                                     sbyteValue,
                                     byteValue2.GetType().Name,
                                     byteValue2);
}
catch (OverflowException) {
   Console.WriteLine("Unable to convert the {0} value {1}.",
                                     sbyteValue.GetType().Name, sbyteValue);
}
// The example displays the following output:
//       Converted the Int32 value 12534 to the Decimal value 12,534.00.
//       Converted the Byte value 255 to the Int32 value 255.
//       Converted the Double value 1.632513E+013 to the Int64 value 16,325,130,000,000.
//       Unable to convert the SByte value -16.

' Convert an Int32 value to a Decimal (a widening conversion).
Dim integralValue As Integer = 12534
Dim decimalValue As Decimal = Convert.ToDecimal(integralValue)
Console.WriteLine("Converted the {0} value {1} to the {2} value {3:N2}.", 
                  integralValue.GetType().Name,
                  integralValue,
                  decimalValue.GetType().Name,
                  decimalValue)

' Convert a Byte value to an Int32 value (a widening conversion).
Dim byteValue As Byte = Byte.MaxValue
Dim integralValue2 As Integer = Convert.ToInt32(byteValue)                                  
Console.WriteLine("Converted the {0} value {1} to " + 
                                  "the {2} value {3:G}.",
                                  byteValue.GetType().Name,
                                  byteValue,
                                  integralValue2.GetType().Name,
                                  integralValue2)

' Convert a Double value to an Int32 value (a narrowing conversion).
Dim doubleValue As Double = 16.32513e12
Try
   Dim longValue As Long = Convert.ToInt64(doubleValue)
   Console.WriteLine("Converted the {0} value {1:E} to " + 
                                     "the {2} value {3:N0}.",
                                     doubleValue.GetType().Name,
                                     doubleValue,
                                     longValue.GetType().Name,
                                     longValue)
Catch e As OverflowException
   Console.WriteLine("Unable to convert the {0:E} value {1}.",
                                     doubleValue.GetType().Name, doubleValue)
End Try                                                             
      
' Convert a signed byte to a byte (a narrowing conversion).     
Dim sbyteValue As SByte = -16
Try
   Dim byteValue2 As Byte = Convert.ToByte(sbyteValue)
   Console.WriteLine("Converted the {0} value {1} to " + 
                                     "the {2} value {3:G}.",
                                     sbyteValue.GetType().Name,
                                     sbyteValue,
                                     byteValue2.GetType().Name,
                                     byteValue2)
Catch e As OverflowException
   Console.WriteLine("Unable to convert the {0} value {1}.",
                                     sbyteValue.GetType().Name, sbyteValue)
End Try 
' The example displays the following output:
'       Converted the Int32 value 12534 to the Decimal value 12,534.00.
'       Converted the Byte value 255 to the Int32 value 255.
'       Converted the Double value 1.632513E+013 to the Int64 value 16,325,130,000,000.
'       Unable to convert the SByte value -16.                                                                  

En algunos casos, en especial al efectuar conversiones directas e inversas de valores de punto flotante, una conversión puede conllevar una pérdida de precisión, aunque no se inicie una excepción OverflowException.In some cases, particularly when converting to and from floating-point values, a conversion may involve a loss of precision, even though it does not throw an OverflowException. En el ejemplo siguiente se muestra esta pérdida de precisión.The following example illustrates this loss of precision. En el primer caso, un valor Decimal tiene menos precisión (menos dígitos significativos) cuando se convierte en el tipo Double.In the first case, a Decimal value has less precision (fewer significant digits) when it is converted to a Double. En el segundo caso, un valor Double se redondea de 42,72 a 43 para completar la conversión.In the second case, a Double value is rounded from 42.72 to 43 in order to complete the conversion.

double doubleValue;

// Convert a Double to a Decimal.
decimal decimalValue = 13956810.96702888123451471211m;
doubleValue = Convert.ToDouble(decimalValue);
Console.WriteLine("{0} converted to {1}.", decimalValue, doubleValue);

doubleValue = 42.72;
try {
   int integerValue = Convert.ToInt32(doubleValue);
   Console.WriteLine("{0} converted to {1}.",
                                     doubleValue, integerValue);
}
catch (OverflowException) {
   Console.WriteLine("Unable to convert {0} to an integer.",
                                     doubleValue);
}
// The example displays the following output:
//       13956810.96702888123451471211 converted to 13956810.9670289.
//       42.72 converted to 43.

Dim doubleValue As Double 

' Convert a Double to a Decimal.
Dim decimalValue As Decimal = 13956810.96702888123451471211d
doubleValue = Convert.ToDouble(decimalValue)
Console.WriteLine("{0} converted to {1}.", decimalValue, doubleValue)

doubleValue = 42.72
Try
   Dim integerValue As Integer = Convert.ToInt32(doubleValue)
   Console.WriteLine("{0} converted to {1}.",
                                     doubleValue, integerValue)
Catch e As OverflowException
   Console.WriteLine("Unable to convert {0} to an integer.",
                                     doubleValue)
End Try   
' The example displays the following output:
'       13956810.96702888123451471211 converted to 13956810.9670289.
'       42.72 converted to 43.

Para obtener una tabla en la que se muestra una lista de conversiones de restricción y ampliación admitidas por la clase Convert, vea Tablas de conversiones de tipos.For a table that lists both the widening and narrowing conversions supported by the Convert class, see Type Conversion Tables.

Conversiones personalizadas con el método ChangeTypeCustom Conversions with the ChangeType Method

Además de admitir las conversiones en cada uno de los tipos base, la clase Convert se puede usar para convertir un tipo personalizado en uno o varios tipos predefinidos.In addition to supporting conversions to each of the base types, the Convert class can be used to convert a custom type to one or more predefined types. El método Convert.ChangeType(Object, Type, IFormatProvider), que a su vez contiene una llamada al método IConvertible.ToType del parámetro value, realiza esta conversión.This conversion is performed by the Convert.ChangeType(Object, Type, IFormatProvider) method, which in turn wraps a call to the IConvertible.ToType method of the value parameter. Esto significa que el objeto representado por el parámetro value debe proporcionar una implementación de la interfaz IConvertible.This means that the object represented by the value parameter must provide an implementation of the IConvertible interface.

En el ejemplo siguiente se muestra una posible implementación de la interfaz IConvertible que permite convertir un objeto TemperatureCelsius en un objeto TemperatureFahrenheit y viceversa.The following example illustrates a possible implementation of the IConvertible interface that allows a TemperatureCelsius object to be converted to a TemperatureFahrenheit object and vice versa. En el ejemplo se define una clase base, Temperature, que implementa la interfaz IConvertible e invalida el método Object.ToString.The example defines a base class, Temperature, that implements the IConvertible interface and overrides the Object.ToString method. Cada una de las clases derivadas TemperatureCelsius y TemperatureFahrenheit invalida los métodos ToType y ToString de la clase base.The derived TemperatureCelsius and TemperatureFahrenheit classes each override the ToType and the ToString methods of the base class.

using System;

public abstract class Temperature : IConvertible
{
   protected decimal temp;

   public Temperature(decimal temperature)
   {
      this.temp = temperature;
   }

   public decimal Value
   {
      get { return this.temp; }
      set { this.temp = value; }
   }

   public override string ToString()
   {
      return temp.ToString(null as IFormatProvider) + "º";
   }

   // IConvertible implementations.
   public TypeCode GetTypeCode() {
      return TypeCode.Object;
   }

   public bool ToBoolean(IFormatProvider provider) {
      throw new InvalidCastException(String.Format("Temperature-to-Boolean conversion is not supported."));
   }

   public byte ToByte(IFormatProvider provider) {
      if (temp < Byte.MinValue || temp > Byte.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the Byte data type.", temp));
      else
         return (byte) temp;
   }

   public char ToChar(IFormatProvider provider) {
      throw new InvalidCastException("Temperature-to-Char conversion is not supported.");
   }

   public DateTime ToDateTime(IFormatProvider provider) {
      throw new InvalidCastException("Temperature-to-DateTime conversion is not supported.");
   }

   public decimal ToDecimal(IFormatProvider provider) {
      return temp;
   }

   public double ToDouble(IFormatProvider provider) {
      return (double) temp;
   }

   public short ToInt16(IFormatProvider provider) {
      if (temp < Int16.MinValue || temp > Int16.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the Int16 data type.", temp));
      else
         return (short) Math.Round(temp);
   }

   public int ToInt32(IFormatProvider provider) {
      if (temp < Int32.MinValue || temp > Int32.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the Int32 data type.", temp));
      else
         return (int) Math.Round(temp);
   }

   public long ToInt64(IFormatProvider provider) {
      if (temp < Int64.MinValue || temp > Int64.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the Int64 data type.", temp));
      else
         return (long) Math.Round(temp);
   }

   public sbyte ToSByte(IFormatProvider provider) {
      if (temp < SByte.MinValue || temp > SByte.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the SByte data type.", temp));
      else
         return (sbyte) temp;
   }

   public float ToSingle(IFormatProvider provider) {
      return (float) temp;
   }

   public virtual string ToString(IFormatProvider provider) {
      return temp.ToString(provider) + "°";
   }

   // If conversionType is implemented by another IConvertible method, call it.
   public virtual object ToType(Type conversionType, IFormatProvider provider) {
      switch (Type.GetTypeCode(conversionType))
      {
         case TypeCode.Boolean:
            return this.ToBoolean(provider);
         case TypeCode.Byte:
            return this.ToByte(provider);
         case TypeCode.Char:
            return this.ToChar(provider);
         case TypeCode.DateTime:
            return this.ToDateTime(provider);
         case TypeCode.Decimal:
            return this.ToDecimal(provider);
         case TypeCode.Double:
            return this.ToDouble(provider);
         case TypeCode.Empty:
            throw new NullReferenceException("The target type is null.");
         case TypeCode.Int16:
            return this.ToInt16(provider);
         case TypeCode.Int32:
            return this.ToInt32(provider);
         case TypeCode.Int64:
            return this.ToInt64(provider);
         case TypeCode.Object:
            // Leave conversion of non-base types to derived classes.
            throw new InvalidCastException(String.Format("Cannot convert from Temperature to {0}.",
                                           conversionType.Name));
         case TypeCode.SByte:
            return this.ToSByte(provider);
         case TypeCode.Single:
            return this.ToSingle(provider);
         case TypeCode.String:
            IConvertible iconv = this;
            return iconv.ToString(provider);
         case TypeCode.UInt16:
            return this.ToUInt16(provider);
         case TypeCode.UInt32:
            return this.ToUInt32(provider);
         case TypeCode.UInt64:
            return this.ToUInt64(provider);
         default:
            throw new InvalidCastException("Conversion not supported.");
      }
   }

   public ushort ToUInt16(IFormatProvider provider) {
      if (temp < UInt16.MinValue || temp > UInt16.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the UInt16 data type.", temp));
      else
         return (ushort) Math.Round(temp);
   }

   public uint ToUInt32(IFormatProvider provider) {
      if (temp < UInt32.MinValue || temp > UInt32.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the UInt32 data type.", temp));
      else
         return (uint) Math.Round(temp);
   }

   public ulong ToUInt64(IFormatProvider provider) {
      if (temp < UInt64.MinValue || temp > UInt64.MaxValue)
         throw new OverflowException(String.Format("{0} is out of range of the UInt64 data type.", temp));
      else
         return (ulong) Math.Round(temp);
   }
}

public class TemperatureCelsius : Temperature, IConvertible
{
   public TemperatureCelsius(decimal value) : base(value)
   {
   }

   // Override ToString methods.
   public override string ToString()
   {
      return this.ToString(null);
   }

   public override string ToString(IFormatProvider provider)
   {
      return temp.ToString(provider) + "°C";
   }

   // If conversionType is a implemented by another IConvertible method, call it.
   public override object ToType(Type conversionType, IFormatProvider provider) {
      // For non-objects, call base method.
      if (Type.GetTypeCode(conversionType) != TypeCode.Object) {
         return base.ToType(conversionType, provider);
      }
      else
      {
         if (conversionType.Equals(typeof(TemperatureCelsius)))
            return this;
         else if (conversionType.Equals(typeof(TemperatureFahrenheit)))
            return new TemperatureFahrenheit((decimal) this.temp * 9 / 5 + 32);
         else
            throw new InvalidCastException(String.Format("Cannot convert from Temperature to {0}.",
                                           conversionType.Name));
      }
   }
}

public class TemperatureFahrenheit : Temperature, IConvertible
{
   public TemperatureFahrenheit(decimal value) : base(value)
   {
   }

   // Override ToString methods.
   public override string ToString()
   {
      return this.ToString(null);
   }

   public override string ToString(IFormatProvider provider)
   {
      return temp.ToString(provider) + "°F";
   }

   public override object ToType(Type conversionType, IFormatProvider provider)
   {
      // For non-objects, call base methood.
      if (Type.GetTypeCode(conversionType) != TypeCode.Object) {
         return base.ToType(conversionType, provider);
      }
      else
      {
         // Handle conversion between derived classes.
         if (conversionType.Equals(typeof(TemperatureFahrenheit)))
            return this;
         else if (conversionType.Equals(typeof(TemperatureCelsius)))
            return new TemperatureCelsius((decimal) (this.temp - 32) * 5 / 9);
         // Unspecified object type: throw an InvalidCastException.
         else
            throw new InvalidCastException(String.Format("Cannot convert from Temperature to {0}.",
                                           conversionType.Name));
      }
   }
}

Public MustInherit Class Temperature
   Implements IConvertible
   
   Protected temp As Decimal
   
   Public Sub New(temperature As Decimal)
      Me.temp = temperature
   End Sub

   Public Property Value As Decimal
      Get 
         Return Me.temp
      End Get
      Set
         Me.temp = Value
      End Set   
   End Property

   Public Overrides Function ToString() As String
      Return temp.ToString() & "º"
   End Function

   ' IConvertible implementations.
   Public Function GetTypeCode() As TypeCode Implements IConvertible.GetTypeCode
      Return TypeCode.Object
   End Function   

   Public Function ToBoolean(provider As IFormatProvider) As Boolean Implements IConvertible.ToBoolean
      Throw New InvalidCastException(String.Format("Temperature-to-Boolean conversion is not supported."))
   End Function
   
   Public Function ToByte(provider As IFormatProvider) As Byte Implements IConvertible.ToByte
      If temp < Byte.MinValue Or temp > Byte.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Byte data type.", temp))
      Else
         Return CByte(temp)
      End If    
   End Function

   Public Function ToChar(provider As IFormatProvider) As Char Implements IConvertible.ToChar
      Throw New InvalidCastException("Temperature-to-Char conversion is not supported.")
   End Function
   
   Public Function ToDateTime(provider As IFormatProvider) As DateTime Implements IConvertible.ToDateTime
      Throw New InvalidCastException("Temperature-to-DateTime conversion is not supported.")
   End Function
   
   Public Function ToDecimal(provider As IFormatProvider) As Decimal Implements IConvertible.ToDecimal
      Return temp
   End Function
   
   Public Function ToDouble(provider As IFormatProvider) As Double Implements IConvertible.ToDouble
      Return CDbl(temp)
   End Function
   
   Public Function ToInt16(provider As IFormatProvider) As Int16 Implements IConvertible.ToInt16
      If temp < Int16.MinValue Or temp > Int16.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Int16 data type.", temp))
      End If
      Return CShort(Math.Round(temp))
   End Function

   Public Function ToInt32(provider As IFormatProvider) As Int32 Implements IConvertible.ToInt32
      If temp < Int32.MinValue Or temp > Int32.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Int32 data type.", temp))
      End If
      Return CInt(Math.Round(temp))
   End Function
   
   Public Function ToInt64(provider As IFormatProvider) As Int64 Implements IConvertible.ToInt64
      If temp < Int64.MinValue Or temp > Int64.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Int64 data type.", temp))
      End If
      Return CLng(Math.Round(temp))
   End Function
   
   Public Function ToSByte(provider As IFormatProvider) As SByte Implements IConvertible.ToSByte
      If temp < SByte.MinValue Or temp > SByte.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the SByte data type.", temp))
      Else
         Return CSByte(temp)
      End If    
   End Function

   Public Function ToSingle(provider As IFormatProvider) As Single Implements IConvertible.ToSingle
      Return CSng(temp)
   End Function
   
   Public Overridable Overloads Function ToString(provider As IFormatProvider) As String Implements IConvertible.ToString
      Return temp.ToString(provider) & " °C"
   End Function
   
   ' If conversionType is a implemented by another IConvertible method, call it.
   Public Overridable Function ToType(conversionType As Type, provider As IFormatProvider) As Object Implements IConvertible.ToType
      Select Case Type.GetTypeCode(conversionType)
         Case TypeCode.Boolean
            Return Me.ToBoolean(provider)
         Case TypeCode.Byte
            Return Me.ToByte(provider)
         Case TypeCode.Char
            Return Me.ToChar(provider)   
         Case TypeCode.DateTime
            Return Me.ToDateTime(provider)
         Case TypeCode.Decimal
            Return Me.ToDecimal(provider)
         Case TypeCode.Double
            Return Me.ToDouble(provider)
         Case TypeCode.Empty
            Throw New NullReferenceException("The target type is null.")
         Case TypeCode.Int16
            Return Me.ToInt16(provider)
         Case TypeCode.Int32
            Return Me.ToInt32(provider)
         Case TypeCode.Int64
            Return Me.ToInt64(provider)
         Case TypeCode.Object
            ' Leave conversion of non-base types to derived classes.
            Throw New InvalidCastException(String.Format("Cannot convert from Temperature to {0}.", _
                                           conversionType.Name))
         Case TypeCode.SByte
            Return Me.ToSByte(provider)
         Case TypeCode.Single
            Return Me.ToSingle(provider)
         Case TypeCode.String
            Return Me.ToString(provider)
         Case TypeCode.UInt16
            Return Me.ToUInt16(provider)
         Case TypeCode.UInt32
            Return Me.ToUInt32(provider)
         Case TypeCode.UInt64
            Return Me.ToUInt64(provider)
         Case Else
            Throw New InvalidCastException("Conversion not supported.")   
      End Select
   End Function
   
   Public Function ToUInt16(provider As IFormatProvider) As UInt16 Implements IConvertible.ToUInt16
      If temp < UInt16.MinValue Or temp > UInt16.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the UInt16 data type.", temp))
      End If
      Return CUShort(Math.Round(temp))
   End Function
   
   Public Function ToUInt32(provider As IFormatProvider) As UInt32 Implements IConvertible.ToUInt32
      If temp < UInt32.MinValue Or temp > UInt32.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the UInt32 data type.", temp))
      End If
      Return CUInt(Math.Round(temp))
   End Function
   
   Public Function ToUInt64(provider As IFormatProvider) As UInt64 Implements IConvertible.ToUInt64
      If temp < UInt64.MinValue Or temp > UInt64.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the UInt64 data type.", temp))
      End If
      Return CULng(Math.Round(temp))
   End Function
End Class

Public Class TemperatureCelsius : Inherits Temperature : Implements IConvertible
   Public Sub New(value As Decimal)
      MyBase.New(value)
   End Sub

   ' Override ToString methods.
   Public Overrides Function ToString() As String
      Return Me.ToString(Nothing)
   End Function

   Public Overrides Function ToString(provider As IFormatProvider ) As String
      Return temp.ToString(provider) + "°C" 
   End Function
   
  ' If conversionType is a implemented by another IConvertible method, call it.
   Public Overrides Function ToType(conversionType As Type, provider As IFormatProvider) As Object
      ' For non-objects, call base method.
      If Type.GetTypeCode(conversionType) <> TypeCode.Object Then
         Return MyBase.ToType(conversionType, provider)
      Else   
         If conversionType.Equals(GetType(TemperatureCelsius)) Then
            Return Me
         ElseIf conversionType.Equals(GetType(TemperatureFahrenheit))
            Return New TemperatureFahrenheit(CDec(Me.temp * 9 / 5 + 32))
         ' Unspecified object type: throw an InvalidCastException.
         Else
            Throw New InvalidCastException(String.Format("Cannot convert from Temperature to {0}.", _ 
                                           conversionType.Name))
         End If
      End If                                  
   End Function
End Class

Public Class TemperatureFahrenheit : Inherits Temperature : Implements IConvertible
   Public Sub New(value As Decimal)
      MyBase.New(value)
   End Sub
   
   ' Override ToString methods.
   Public Overrides Function ToString() As String
      Return Me.ToString(Nothing)
   End Function

   Public Overrides Function ToString(provider As IFormatProvider ) As String
      Return temp.ToString(provider) + "°F" 
   End Function
   
   Public Overrides Function ToType(conversionType As Type, provider As IFormatProvider) As Object
      ' For non-objects, call base methood.
      If Type.GetTypeCode(conversionType) <> TypeCode.Object Then
         Return MyBase.ToType(conversionType, provider)
      Else   
         ' Handle conversion between derived classes.
         If conversionType.Equals(GetType(TemperatureFahrenheit)) Then 
            Return Me
         ElseIf conversionType.Equals(GetType(TemperatureCelsius))
            Return New TemperatureCelsius(CDec((MyBase.temp - 32) * 5 / 9))
         ' Unspecified object type: throw an InvalidCastException.
         Else
            Throw New InvalidCastException(String.Format("Cannot convert from Temperature to {0}.", _
                                           conversionType.Name))
         End If
      End If                                  
   End Function
End Class   

En el ejemplo siguiente se muestran varias llamadas a estas implementaciones de IConvertible para convertir los objetos TemperatureCelsius en objetos TemperatureFahrenheit y viceversa.The following example illustrates several calls to these IConvertible implementations to convert TemperatureCelsius objects to TemperatureFahrenheit objects and vice versa.

TemperatureCelsius tempC1 = new TemperatureCelsius(0);
TemperatureFahrenheit tempF1 = (TemperatureFahrenheit) Convert.ChangeType(tempC1, typeof(TemperatureFahrenheit), null);
Console.WriteLine("{0} equals {1}.", tempC1, tempF1);
TemperatureCelsius tempC2 = (TemperatureCelsius) Convert.ChangeType(tempC1, typeof(TemperatureCelsius), null);
Console.WriteLine("{0} equals {1}.", tempC1, tempC2);
TemperatureFahrenheit tempF2 = new TemperatureFahrenheit(212);
TemperatureCelsius tempC3 = (TemperatureCelsius) Convert.ChangeType(tempF2, typeof(TemperatureCelsius), null);
Console.WriteLine("{0} equals {1}.", tempF2, tempC3);
TemperatureFahrenheit tempF3 = (TemperatureFahrenheit) Convert.ChangeType(tempF2, typeof(TemperatureFahrenheit), null);
Console.WriteLine("{0} equals {1}.", tempF2, tempF3);
// The example displays the following output:
//       0°C equals 32°F.
//       0°C equals 0°C.
//       212°F equals 100°C.
//       212°F equals 212°F.

Dim tempC1 As New TemperatureCelsius(0)
Dim tempF1 As TemperatureFahrenheit = CType(Convert.ChangeType(tempC1, GetType(TemperatureFahrenheit), Nothing), TemperatureFahrenheit)
Console.WriteLine("{0} equals {1}.", tempC1, tempF1) 
Dim tempC2 As TemperatureCelsius = CType(Convert.ChangeType(tempC1, GetType(TemperatureCelsius), Nothing), TemperatureCelsius)
Console.WriteLine("{0} equals {1}.", tempC1, tempC2) 
Dim tempF2 As New TemperatureFahrenheit(212)
Dim tempC3 As TEmperatureCelsius = CType(Convert.ChangeType(tempF2, GEtType(TemperatureCelsius), Nothing), TemperatureCelsius)
Console.WriteLine("{0} equals {1}.", tempF2, tempC3) 
Dim tempF3 As TemperatureFahrenheit = CType(Convert.ChangeType(tempF2, GetType(TemperatureFahrenheit), Nothing), TemperatureFahrenheit)
Console.WriteLine("{0} equals {1}.", tempF2, tempF3)
' The example displays the following output:
'       0°C equals 32°F.
'       0°C equals 0°C.
'       212°F equals 100°C.
'       212°F equals 212°F.      

Clase TypeConverterThe TypeConverter Class

.NET Framework también permite definir un convertidor de tipos para un tipo personalizado extendiendo la clase System.ComponentModel.TypeConverter y asociando el convertidor de tipos al tipo mediante un atributo System.ComponentModel.TypeConverterAttribute.The .NET Framework also allows you to define a type converter for a custom type by extending the System.ComponentModel.TypeConverter class and associating the type converter with the type through a System.ComponentModel.TypeConverterAttribute attribute. En la tabla siguiente se resaltan las diferencias entre este enfoque y la implementación de la interfaz IConvertible para un tipo personalizado.The following table highlights the differences between this approach and implementing the IConvertible interface for a custom type.

Para obtener más información sobre cómo usar convertidores de tipos para realizar conversiones, vea System.ComponentModel.TypeConverter.For more information about using type converters to perform conversions, see System.ComponentModel.TypeConverter.

Vea tambiénSee also

• System.Convert
• IConvertible
• Tablas de conversión de tiposType Conversion Tables