Convert.ChangeType Metodo

public:
 static System::Object ^ ChangeType(System::Object ^ value, Type ^ conversionType);

public static object ChangeType (object value, Type conversionType);

public static object ChangeType (object value, Type? conversionType);

static member ChangeType : obj * Type -> obj

Public Shared Function ChangeType (value As Object, conversionType As Type) As Object

Parametri

Restituisce

Object

Oggetto il cui tipo è conversionType e il cui valore è equivalente a value.An object whose type is conversionType and whose value is equivalent to value.

-oppure--or-

Riferimento Null (Nothing in Visual Basic), se value è null e conversionType non è un tipo di valore.A null reference (Nothing in Visual Basic), if value is null and conversionType is not a value type.

Eccezioni

Esempio

Nell'esempio riportato di seguito viene illustrato l'utilizzo del metodo ChangeType.The following example illustrates the use of the ChangeType method.

using namespace System;

int main()
{
   Double d = -2.345;
   int i =  *safe_cast<Int32^>(Convert::ChangeType( d, int::typeid ));
   Console::WriteLine( "The double value {0} when converted to an int becomes {1}", d, i );
   String^ s = "12/12/98";
   DateTime dt =  *safe_cast<DateTime^>(Convert::ChangeType( s, DateTime::typeid ));
   Console::WriteLine( "The string value {0} when converted to a Date becomes {1}", s, dt );
}

using System;

public class ChangeTypeTest {
    public static void Main() {

        Double d = -2.345;
        int i = (int)Convert.ChangeType(d, typeof(int));

        Console.WriteLine("The double value {0} when converted to an int becomes {1}", d, i);

        string s = "12/12/98";
        DateTime dt = (DateTime)Convert.ChangeType(s, typeof(DateTime));

        Console.WriteLine("The string value {0} when converted to a Date becomes {1}", s, dt);
    }
}

Public Class ChangeTypeTest
    
    Public Shared Sub Main()
        Dim d As [Double] = - 2.345
        Dim i As Integer = CInt(Convert.ChangeType(d, GetType(Integer)))
        
        Console.WriteLine("The double value {0} when converted to an int becomes {1}", d, i)
        Dim s As String = "12/12/98"
        Dim dt As DateTime = CType(Convert.ChangeType(s, GetType(DateTime)), DateTime)
        
        Console.WriteLine("The string value {0} when converted to a Date becomes {1}", s, dt)
    End Sub
End Class

Commenti

ChangeType è un metodo di conversione di utilizzo generico che converte l'oggetto specificato da value in conversionType .ChangeType is a general-purpose conversion method that converts the object specified by value to conversionType. Il value parametro può essere un oggetto di qualsiasi tipo e conversionType può anche essere un Type oggetto che rappresenta qualsiasi tipo di base o personalizzato.The value parameter can be an object of any type, and conversionType can also be a Type object that represents any base or custom type. Affinché la conversione abbia esito positivo, value deve implementare l' IConvertible interfaccia, perché il metodo esegue semplicemente il wrapping di una chiamata a un IConvertible metodo appropriato.For the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. Il metodo richiede che la conversione value di conversionType sia supportata.The method requires that conversion of value to conversionType be supported.

Questo metodo usa le impostazioni cultura del thread corrente per la conversione.This method uses the current thread's culture for the conversion.

Note per i chiamanti

Il ChangeType(Object, Type) metodo può convertire un valore di enumerazione in un altro tipo.The ChangeType(Object, Type) method can convert an enumeration value to another type. Tuttavia, non è in grado di convertire un altro tipo in un valore di enumerazione, anche se il tipo di origine è il tipo sottostante dell'enumerazione.However, it cannot convert another type to an enumeration value, even if the source type is the underlying type of the enumeration. Per convertire un tipo in un valore di enumerazione, usare un operatore di cast (in C#) o una funzione di conversione (in Visual Basic).To convert a type to an enumeration value, use a casting operator (in C#) or a conversion function (in Visual Basic). Nell'esempio seguente viene illustrata la conversione da e verso un valore di enumerazione continente .The following example illustrates the conversion to and from a Continent enumeration value.

::: Code Language = "CSharp" Source = "~/Samples/Snippets/CSharp/VS_Snippets_CLR_System/System.Convert.ChangeType/CS/changetype_enum2. cs" Interactive = "try-dotnet" ID = "Snippet5":::::: Code Language = "VB" Source = "~/Samples/Snippets/VisualBasic/VS_Snippets_CLR_System/System.Convert.ChangeType/VB/changetype_enum2. vb" ID = "Snippet5"::::::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.convert.changetype/cs/changetype_enum2.cs" interactive="try-dotnet" id="Snippet5"::: :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.convert.changetype/vb/changetype_enum2.vb" id="Snippet5":::

Il ChangeType(Object, Type) metodo può convertire un tipo nullable in un altro tipo.The ChangeType(Object, Type) method can convert a nullable type to another type. Tuttavia, non può convertire un altro tipo in un valore di un tipo nullable, anche se conversionType è il tipo sottostante di Nullable<T> . Per eseguire la conversione, è possibile usare un operatore di cast (in C#) o una funzione di conversione (in Visual Basic).However, it cannot convert another type to a value of a nullable type, even if conversionType is the underlying type of the Nullable<T>.To perform the conversion, you can use a casting operator (in C#) or a conversion function (in Visual Basic). Nell'esempio seguente viene illustrata la conversione da e verso un tipo Nullable.The following example illustrates the conversion to and from a nullable type.

::: Code Language = "CSharp" Source = "~/Samples/Snippets/CSharp/VS_Snippets_CLR_System/System.Convert.ChangeType/CS/changetype_nullable. cs" Interactive = "try-dotnet" ID = "Snippet7":::::: Code Language = "VB" Source = "~/Samples/Snippets/VisualBasic/VS_Snippets_CLR_System/System.Convert.ChangeType/VB/changetype_nullable. vb" ID = "Snippet7"::::::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.convert.changetype/cs/changetype_nullable.cs" interactive="try-dotnet" id="Snippet7"::: :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.convert.changetype/vb/changetype_nullable.vb" id="Snippet7":::

public:
 static System::Object ^ ChangeType(System::Object ^ value, TypeCode typeCode);

public static object ChangeType (object value, TypeCode typeCode);

static member ChangeType : obj * TypeCode -> obj

Public Shared Function ChangeType (value As Object, typeCode As TypeCode) As Object

Parametri

Restituisce

Object

Oggetto il cui tipo sottostante è typeCode e il cui valore è equivalente a value.An object whose underlying type is typeCode and whose value is equivalent to value.

-oppure--or-

Riferimento Null (Nothing in Visual Basic), se value è null e typeCode è Empty, String o Object.A null reference (Nothing in Visual Basic), if value is null and typeCode is Empty, String, or Object.

Eccezioni

Esempio

Nell'esempio seguente viene illustrato come utilizzare il ChangeType(Object, TypeCode) metodo per modificare un oggetto Object nel tipo specificato dal TypeCode parametro, se possibile.The following example illustrates how to use the ChangeType(Object, TypeCode) method to change an Object to the type specified by the TypeCode parameter, if possible.

using namespace System;

void main()
{
   Double d = -2.345;
   int i = (int) Convert::ChangeType(d, TypeCode::Int32);

   Console::WriteLine("The Double {0} when converted to an Int32 is {1}", d, i);

   String^ s = "12/12/2009";
   DateTime dt = (DateTime)Convert::ChangeType(s, DateTime::typeid);

   Console::WriteLine("The String {0} when converted to a Date is {1}", s, dt);        
}
// The example displays the following output:
//    The Double -2.345 when converted to an Int32 is -2
//    The String 12/12/2009 when converted to a Date is 12/12/2009 12:00:00 AM

using System;

public class ChangeTypeTest {
    public static void Main() {

        Double d = -2.345;
        int i = (int)Convert.ChangeType(d, TypeCode.Int32);

        Console.WriteLine("The Double {0} when converted to an Int32 is {1}", d, i);

        string s = "12/12/2009";
        DateTime dt = (DateTime)Convert.ChangeType(s, typeof(DateTime));

        Console.WriteLine("The String {0} when converted to a Date is {1}", s, dt);
    }
}
// The example displays the following output:
//    The Double -2.345 when converted to an Int32 is -2
//    The String 12/12/2009 when converted to a Date is 12/12/2009 12:00:00 AM

Public Class ChangeTypeTest
    
    Public Shared Sub Main()
        Dim d As [Double] = - 2.345
        Dim i As Integer = CInt(Convert.ChangeType(d, TypeCode.Int32))
        
        Console.WriteLine("The Double {0} when converted to an Int32 is {1}", d, i)
        Dim s As String = "12/12/2009"
        Dim dt As DateTime = CDate(Convert.ChangeType(s, TypeCode.DateTime))
        
        Console.WriteLine("The String {0} when converted to a Date is {1}", s, dt)
    End Sub 
End Class 
' The example displays the following output:
'    The Double -2.345 when converted to an Int32 is -2
'    The String 12/12/2009 when converted to a Date is 12/12/2009 12:00:00 AM

Commenti

ChangeType(Object, TypeCode) è un metodo di conversione di utilizzo generico che converte l'oggetto specificato da value in un tipo predefinito specificato da typeCode .ChangeType(Object, TypeCode) is a general-purpose conversion method that converts the object specified by value to a predefined type specified by typeCode. Il value parametro può essere un oggetto di qualsiasi tipo.The value parameter can be an object of any type. Affinché la conversione abbia esito positivo, value deve implementare l' IConvertible interfaccia, perché il metodo esegue semplicemente il wrapping di una chiamata a un IConvertible metodo appropriato.For the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. Il metodo richiede anche che la conversione value di typeCode sia supportata.The method also requires that conversion of value to typeCode be supported.

Il ChangeType(Object, TypeCode) metodo non supporta la conversione di value in un tipo personalizzato.The ChangeType(Object, TypeCode) method does not support the conversion of value to a custom type. Per eseguire tale conversione, chiamare il ChangeType(Object, Type) metodo.To perform such a conversion, call the ChangeType(Object, Type) method.

public:
 static System::Object ^ ChangeType(System::Object ^ value, Type ^ conversionType, IFormatProvider ^ provider);

public static object ChangeType (object value, Type conversionType, IFormatProvider provider);

public static object ChangeType (object value, Type? conversionType, IFormatProvider provider);

static member ChangeType : obj * Type * IFormatProvider -> obj

Public Shared Function ChangeType (value As Object, conversionType As Type, provider As IFormatProvider) As Object

Parametri

Restituisce

Object

Oggetto il cui tipo è conversionType e il cui valore è equivalente a value.An object whose type is conversionType and whose value is equivalent to value.

-oppure--or-

value, se gli attributi Type di value e conversionType sono uguali.value, if the Type of value and conversionType are equal.

-oppure--or-

Riferimento Null (Nothing in Visual Basic), se value è null e conversionType non è un tipo di valore.A null reference (Nothing in Visual Basic), if value is null and conversionType is not a value type.

Eccezioni

Esempio

Nell'esempio seguente viene definita una classe Temperature che implementa l'interfaccia IConvertible .The following example defines a Temperature class that implements the IConvertible interface.

using namespace System;
using namespace System::Globalization;

public ref class Temperature : IConvertible
{
private:
   Decimal m_Temp;

public:
   Temperature(Decimal temperature)
   {
      m_Temp = temperature;
   }
   
   property Decimal Celsius {
      Decimal get() { return m_Temp; }
   }
   
   property Decimal Kelvin {
      Decimal get() { return m_Temp + (Decimal) 273.15; }
   }
   
   property Decimal Fahrenheit {
      Decimal get() { return Math::Round((Decimal) (m_Temp * 9 / 5 + 32), 2); }
   }
   
   virtual String^ ToString()
   override {
      return m_Temp.ToString("N2") + "�C";
   }

   // IConvertible implementations.
   virtual TypeCode GetTypeCode()
   {
      return TypeCode::Object;
   }
   
   virtual bool ToBoolean(IFormatProvider^ provider) 
   {
      if (m_Temp == 0)
         return false;
      else
         return true;
   } 
   
   virtual Byte ToByte(IFormatProvider^ provider)
   {
      if (m_Temp < Byte::MinValue || m_Temp > Byte::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the Byte type.", 
                                                   m_Temp));
      else
         return Decimal::ToByte(m_Temp);
   }
   
   virtual Char ToChar(IFormatProvider^ provider)
   {
      throw gcnew InvalidCastException("Temperature to Char conversion is not supported.");
   } 
   
   virtual DateTime ToDateTime(IFormatProvider^ provider)
   {
      throw gcnew InvalidCastException("Temperature to DateTime conversion is not supported.");
   }
   
   virtual Decimal ToDecimal(IFormatProvider^ provider)
   {
      return m_Temp;
   }
   
   virtual Double ToDouble(IFormatProvider^ provider)
   {
      return Decimal::ToDouble(m_Temp);
   }   
   
   virtual Int16 ToInt16(IFormatProvider^ provider)
   {
      if (m_Temp < Int16::MinValue || m_Temp > Int16::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the Int16 type.",
                                                   m_Temp));
      else
         return Decimal::ToInt16(m_Temp);
   }
   
   virtual Int32 ToInt32(IFormatProvider^ provider)
      {
      if (m_Temp < Int32::MinValue || m_Temp > Int32::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the Int32 type.",
                                                   m_Temp));
      else
         return Decimal::ToInt32(m_Temp);
   }
   
   virtual Int64 ToInt64(IFormatProvider^ provider)
   {
      if (m_Temp < Int64::MinValue || m_Temp > Int64::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the Int64 type.",
                                                   m_Temp));
      else
         return Decimal::ToInt64(m_Temp);
   }
   
   virtual SByte ToSByte(IFormatProvider^ provider)
   {
      if (m_Temp < SByte::MinValue || m_Temp > SByte::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the SByte type.",
                                                   m_Temp));
      else
         return Decimal::ToSByte(m_Temp);
   }

   virtual Single ToSingle(IFormatProvider^ provider)
   {
      return Decimal::ToSingle(m_Temp);
   }

   virtual String^ ToString(IFormatProvider^ provider)
   {
      return m_Temp.ToString("N2", provider) + "�C";
   }
   
   virtual Object^ ToType(Type^ conversionType, IFormatProvider^ provider)
   {
      switch (Type::GetTypeCode(conversionType))
      {
      case TypeCode::Boolean: 
            return ToBoolean(nullptr);
      case TypeCode::Byte:
            return ToByte(nullptr);
      case TypeCode::Char:
            return ToChar(nullptr);
      case TypeCode::DateTime:
            return ToDateTime(nullptr);
      case TypeCode::Decimal:
            return ToDecimal(nullptr);
      case TypeCode::Double:
            return ToDouble(nullptr);
      case TypeCode::Int16:
            return ToInt16(nullptr);
      case TypeCode::Int32:
            return ToInt32(nullptr);
      case TypeCode::Int64:
            return ToInt64(nullptr);
      case TypeCode::Object:
            if (Temperature::typeid->Equals(conversionType))
               return this;
            else
               throw gcnew InvalidCastException(String::Format("Conversion to a {0} is not supported.",
                                                            conversionType->Name));
      case TypeCode::SByte:
            return ToSByte(nullptr);
      case TypeCode::Single:
            return ToSingle(nullptr);
      case TypeCode::String:
            return ToString(provider);
      case TypeCode::UInt16:
            return ToUInt16(nullptr);
      case TypeCode::UInt32:
            return ToUInt32(nullptr);
      case TypeCode::UInt64:
            return ToUInt64(nullptr);   
         default:
            throw gcnew InvalidCastException(String::Format("Conversion to {0} is not supported.", conversionType->Name));   
      }
   }
   
   virtual UInt16 ToUInt16(IFormatProvider^ provider)
   {
      if (m_Temp < UInt16::MinValue || m_Temp > UInt16::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the UInt16 type.",
                                                   m_Temp));
      else
         return Decimal::ToUInt16(m_Temp);
   }

   virtual UInt32 ToUInt32(IFormatProvider^ provider)
   {
      if (m_Temp < UInt32::MinValue || m_Temp > UInt32::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the UInt32 type.",
                                                   m_Temp));
      else
         return Decimal::ToUInt32(m_Temp);
   }
   
   virtual UInt64 ToUInt64(IFormatProvider^ provider)
   {
      if (m_Temp < UInt64::MinValue || m_Temp > UInt64::MaxValue)
         throw gcnew OverflowException(String::Format("{0} is out of range of the UInt64 type.",
                                                   m_Temp));
      else
         return Decimal::ToUInt64(m_Temp);
   }
};

using System;
using System.Globalization;

public class Temperature : IConvertible
{
   private decimal m_Temp;

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

   public decimal Celsius
   {
      get { return this.m_Temp; }
   }

   public decimal Kelvin
   {
      get { return this.m_Temp + 273.15m; }
   }

   public decimal Fahrenheit
   {
      get { return Math.Round((decimal) (this.m_Temp * 9 / 5 + 32), 2); }
   }

   public override string ToString()
   {
      return m_Temp.ToString("N2") + "°C";
   }

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

   public bool ToBoolean(IFormatProvider provider)
   {
      if (m_Temp == 0)
         return false;
      else
         return true;
   }

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

   public double ToDouble(IFormatProvider provider)
   {
      return Decimal.ToDouble(this.m_Temp);
   }

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

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

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

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

   public float ToSingle(IFormatProvider provider)
   {
      return Decimal.ToSingle(this.m_Temp);
   }

   public string ToString(IFormatProvider provider)
   {
      return m_Temp.ToString("N2", provider) + "°C";
   }

   public object ToType(Type conversionType, IFormatProvider provider)
   {
      switch (Type.GetTypeCode(conversionType))
      {
         case TypeCode.Boolean:
            return this.ToBoolean(null);
         case TypeCode.Byte:
            return this.ToByte(null);
         case TypeCode.Char:
            return this.ToChar(null);
         case TypeCode.DateTime:
            return this.ToDateTime(null);
         case TypeCode.Decimal:
            return this.ToDecimal(null);
         case TypeCode.Double:
            return this.ToDouble(null);
         case TypeCode.Int16:
            return this.ToInt16(null);
         case TypeCode.Int32:
            return this.ToInt32(null);
         case TypeCode.Int64:
            return this.ToInt64(null);
         case TypeCode.Object:
            if (typeof(Temperature).Equals(conversionType))
               return this;
            else
               throw new InvalidCastException(String.Format("Conversion to a {0} is not supported.",
                                                            conversionType.Name));
         case TypeCode.SByte:
            return this.ToSByte(null);
         case TypeCode.Single:
            return this.ToSingle(null);
         case TypeCode.String:
            return this.ToString(provider);
         case TypeCode.UInt16:
            return this.ToUInt16(null);
         case TypeCode.UInt32:
            return this.ToUInt32(null);
         case TypeCode.UInt64:
            return this.ToUInt64(null);
         default:
            throw new InvalidCastException(String.Format("Conversion to {0} is not supported.", conversionType.Name));
      }
   }

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

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

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

Imports System.Globalization

Public Class Temperature : Implements IConvertible
   Private m_Temp As Decimal

   Public Sub New(temperature As Decimal)
      Me.m_Temp = temperature
   End Sub
   
   Public ReadOnly Property Celsius() As Decimal
      Get
         Return Me.m_Temp
      End Get   
   End Property
   
   Public ReadOnly Property Kelvin() As Decimal
      Get
         Return Me.m_Temp + 273.15d   
      End Get
   End Property
   
   Public ReadOnly Property Fahrenheit() As Decimal
      Get
         Return Math.Round(CDec(Me.m_Temp * 9 / 5 + 32), 2)
      End Get      
   End Property
   
   Public Overrides Function ToString() As String
      Return m_Temp.ToString("N2") & "°C"
   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
      If m_Temp = 0 Then
         Return False
      Else
         Return True
      End If
   End Function 
   
   Public Function ToByte(provider As IFormatProvider) As Byte _
                   Implements IConvertible.ToByte
      If m_Temp < Byte.MinValue Or m_Temp > Byte.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Byte type.", _ 
                                                   Me.m_Temp)) 
      Else
         Return Decimal.ToByte(Me.m_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 Date _
                   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 Me.m_Temp
   End Function
   
   Public Function ToDouble(provider As IFormatProvider) As Double _
                   Implements IConvertible.ToDouble
      Return Decimal.ToDouble(Me.m_Temp)
   End Function   
   
   Public Function ToInt16(provider As IFormatProvider) As Int16 _
                   Implements IConvertible.ToInt16
      If Me.m_Temp < Int16.MinValue Or Me.m_Temp > Int16.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Int16 type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToInt16(Me.m_Temp)   
      End If
   End Function
   
   Public Function ToInt32(provider As IFormatProvider) As Int32 _
                   Implements IConvertible.ToInt32
      If Me.m_Temp < Int32.MinValue Or Me.m_Temp > Int32.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Int32 type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToInt32(Me.m_Temp)
      End If      
   End Function
   
   Public Function ToInt64(provider As IFormatProvider) As Int64 _
                   Implements IConvertible.ToInt64
      If Me.m_Temp < Int64.MinValue Or Me.m_Temp > Int64.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the Int64 type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToInt64(Me.m_Temp)
      End If      
   End Function
   
   Public Function ToSByte(provider As IFormatProvider) As SByte _
                   Implements IConvertible.ToSByte
      If Me.m_Temp < SByte.MinValue Or Me.m_Temp > SByte.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the SByte type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToSByte(Me.m_Temp)
      End If      
   End Function

   Public Function ToSingle(provider As IFormatProvider) As Single _
                   Implements IConvertible.ToSingle
      Return Decimal.ToSingle(Me.m_Temp)
   End Function

   Public Overloads Function ToString(provider As IFormatProvider) As String _
                   Implements IConvertible.ToString
      Return m_Temp.ToString("N2", provider) & "°C"
   End Function
   
   Public Function ToType(conversionType As Type, provider As IFormatProvider) As Object _
                   Implements IConvertible.ToType
      Select Case Type.GetTypeCode(conversionType)
         Case TypeCode.Boolean 
            Return Me.ToBoolean(Nothing)
         Case TypeCode.Byte
            Return Me.ToByte(Nothing)
         Case TypeCode.Char
            Return Me.ToChar(Nothing)
         Case TypeCode.DateTime
            Return Me.ToDateTime(Nothing)
         Case TypeCode.Decimal
            Return Me.ToDecimal(Nothing)
         Case TypeCode.Double
            Return Me.ToDouble(Nothing)
         Case TypeCode.Int16
            Return Me.ToInt16(Nothing)
         Case TypeCode.Int32
            Return Me.ToInt32(Nothing)
         Case TypeCode.Int64
            Return Me.ToInt64(Nothing)
         Case TypeCode.Object
            If GetType(Temperature).Equals(conversionType) Then
               Return Me
            Else
               Throw New InvalidCastException(String.Format("Conversion to a {0} is not supported.", _
                                                            conversionType.Name))
            End If 
         Case TypeCode.SByte
            Return Me.ToSByte(Nothing)
         Case TypeCode.Single
            Return Me.ToSingle(Nothing)
         Case TypeCode.String
            Return Me.ToString(provider)
         Case TypeCode.UInt16
            Return Me.ToUInt16(Nothing)
         Case TypeCode.UInt32
            Return Me.ToUInt32(Nothing)
         Case TypeCode.UInt64
            Return Me.ToUInt64(Nothing)   
         Case Else
            Throw New InvalidCastException(String.Format("Conversion to {0} is not supported.", conversionType.Name))   
      End Select
   End Function
   
   Public Function ToUInt16(provider As IFormatProvider) As UInt16 _
                   Implements IConvertible.ToUInt16
      If Me.m_Temp < UInt16.MinValue Or Me.m_Temp > UInt16.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the UInt16 type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToUInt16(Me.m_Temp)
      End If   
   End Function

   Public Function ToUInt32(provider As IFormatProvider) As UInt32 _
                   Implements IConvertible.ToUInt32
      If Me.m_Temp < UInt32.MinValue Or Me.m_Temp > UInt32.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the UInt32 type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToUInt32(Me.m_Temp)
      End If   
   End Function
   
   Public Function ToUInt64(provider As IFormatProvider) As UInt64 _
                   Implements IConvertible.ToUInt64
      If Me.m_Temp < UInt64.MinValue Or Me.m_Temp > UInt64.MaxValue Then
         Throw New OverflowException(String.Format("{0} is out of range of the UInt64 type.", _
                                                   Me.m_Temp))
      Else
         Return Decimal.ToUInt64(Me.m_temp)
      End If   
   End Function
End Class

Nell'esempio seguente viene creata un'istanza della Temperature classe e viene chiamato il ChangeType(Object, Type, IFormatProvider) metodo per convertirlo nei tipi numerici di base supportati da .NET e in un oggetto String .The following example creates an instance of the Temperature class and calls the ChangeType(Object, Type, IFormatProvider) method to convert it to the basic numeric types supported by .NET and to a String. Viene illustrato che il ChangeType metodo esegue il wrapping di una chiamata all'implementazione del tipo di origine IConvertible .It illustrates that the ChangeType method wraps a call to the source type's IConvertible implementation.

void main()
{     
   Temperature^ cool = gcnew Temperature(5);
   array<Type^>^ targetTypes = gcnew array<Type^> { SByte::typeid, Int16::typeid, Int32::typeid,
                                                    Int64::typeid, Byte::typeid, UInt16::typeid,
                                                    UInt32::typeid, UInt64::typeid, Decimal::typeid,
                                                    Single::typeid, Double::typeid, String::typeid };
   CultureInfo^ provider = gcnew CultureInfo("fr-FR");
      
   for each (Type^ targetType in targetTypes)
   {
      try {
         Object^ value = Convert::ChangeType(cool, targetType, provider);
         Console::WriteLine("Converted {0} {1} to {2} {3}.",
                           cool->GetType()->Name, cool->ToString(),
                           targetType->Name, value);
      }
      catch (InvalidCastException^) {
         Console::WriteLine("Unsupported {0} --> {1} conversion.",
                           cool->GetType()->Name, targetType->Name);
      }                     
      catch (OverflowException^) {
         Console::WriteLine("{0} is out of range of the {1} type.",
                           cool, targetType->Name);
      }
   }
}
// The example dosplays the following output:
//       Converted Temperature 5.00�C to SByte 5.
//       Converted Temperature 5.00�C to Int16 5.
//       Converted Temperature 5.00�C to Int32 5.
//       Converted Temperature 5.00�C to Int64 5.
//       Converted Temperature 5.00�C to Byte 5.
//       Converted Temperature 5.00�C to UInt16 5.
//       Converted Temperature 5.00�C to UInt32 5.
//       Converted Temperature 5.00�C to UInt64 5.
//       Converted Temperature 5.00�C to Decimal 5.
//       Converted Temperature 5.00�C to Single 5.
//       Converted Temperature 5.00�C to Double 5.
//       Converted Temperature 5.00�C to String 5,00�C.

public class Example
{
   public static void Main()
   {
      Temperature cool = new Temperature(5);
      Type[] targetTypes = { typeof(SByte), typeof(Int16), typeof(Int32),
                             typeof(Int64), typeof(Byte), typeof(UInt16),
                             typeof(UInt32), typeof(UInt64), typeof(Decimal),
                             typeof(Single), typeof(Double), typeof(String) };
      CultureInfo provider = new CultureInfo("fr-FR");

      foreach (Type targetType in targetTypes)
      {
         try {
            object value = Convert.ChangeType(cool, targetType, provider);
            Console.WriteLine("Converted {0} {1} to {2} {3}.",
                              cool.GetType().Name, cool.ToString(),
                              targetType.Name, value);
         }
         catch (InvalidCastException) {
            Console.WriteLine("Unsupported {0} --> {1} conversion.",
                              cool.GetType().Name, targetType.Name);
         }
         catch (OverflowException) {
            Console.WriteLine("{0} is out of range of the {1} type.",
                              cool, targetType.Name);
         }
      }
   }
}
// The example dosplays the following output:
//       Converted Temperature 5.00°C to SByte 5.
//       Converted Temperature 5.00°C to Int16 5.
//       Converted Temperature 5.00°C to Int32 5.
//       Converted Temperature 5.00°C to Int64 5.
//       Converted Temperature 5.00°C to Byte 5.
//       Converted Temperature 5.00°C to UInt16 5.
//       Converted Temperature 5.00°C to UInt32 5.
//       Converted Temperature 5.00°C to UInt64 5.
//       Converted Temperature 5.00°C to Decimal 5.
//       Converted Temperature 5.00°C to Single 5.
//       Converted Temperature 5.00°C to Double 5.
//       Converted Temperature 5.00°C to String 5,00°C.

Module Example
   Public Sub Main()
      Dim cool As New Temperature(5)
      Dim targetTypes() As Type = { GetType(SByte), GetType(Int16), GetType(Int32), _
                                    GetType(Int64), GetType(Byte), GetType(UInt16), _
                                    GetType(UInt32), GetType(UInt64), GetType(Decimal), _
                                    GetType(Single), GetType(Double), GetType(String) }
      Dim provider As New CultureInfo("fr-FR")
      
      For Each targetType As Type In targetTypes
         Try
            Dim value As Object = Convert.ChangeType(cool, targetType, provider)
            Console.WriteLine("Converted {0} {1} to {2} {3}.", _
                              cool.GetType().Name, cool.ToString(), _
                              targetType.Name, value)
         Catch e As InvalidCastException
            Console.WriteLine("Unsupported {0} --> {1} conversion.", _
                              cool.GetType().Name, targetType.Name)
         Catch e As OverflowException
            Console.WriteLine("{0} is out of range of the {1} type.", _
                              cool, targetType.Name)
         End Try                     
      Next
   End Sub
End Module
' The example displays the following output:
'       Converted Temperature 5.00°C to SByte 5.
'       Converted Temperature 5.00°C to Int16 5.
'       Converted Temperature 5.00°C to Int32 5.
'       Converted Temperature 5.00°C to Int64 5.
'       Converted Temperature 5.00°C to Byte 5.
'       Converted Temperature 5.00°C to UInt16 5.
'       Converted Temperature 5.00°C to UInt32 5.
'       Converted Temperature 5.00°C to UInt64 5.
'       Converted Temperature 5.00°C to Decimal 5.
'       Converted Temperature 5.00°C to Single 5.
'       Converted Temperature 5.00°C to Double 5.
'       Converted Temperature 5.00°C to String 5,00°C.

Commenti

ChangeType è un metodo di conversione di utilizzo generico che converte l'oggetto specificato da value in conversionType .ChangeType is a general-purpose conversion method that converts the object specified by value to conversionType. Il value parametro può essere un oggetto di qualsiasi tipo e conversionType può anche essere un Type oggetto che rappresenta qualsiasi tipo di base o personalizzato.The value parameter can be an object of any type, and conversionType can also be a Type object that represents any base or custom type. Affinché la conversione abbia esito positivo, value deve implementare l' IConvertible interfaccia, perché il metodo esegue semplicemente il wrapping di una chiamata a un IConvertible metodo appropriato.For the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. Il metodo richiede che la conversione value di conversionType sia supportata.The method requires that conversion of value to conversionType be supported.

Il provider parametro è un' IFormatProvider implementazione di che fornisce informazioni sulla formattazione per la conversione.The provider parameter is an IFormatProvider implementation that supplies formatting information for the conversion. L'utilizzo di questo parametro dipende dall' IConvertible implementazione sottostante.Whether and how this parameter is used depends on the underlying IConvertible implementation. Se value è un tipo di dati di base, provider viene utilizzato solo per le conversioni seguenti:If value is a base data type, provider is used only for the following conversions:

• Conversione da un numero a una stringa o da una stringa a un numero.Conversion from a number to a string, or from a string to a number. provider deve essere un CultureInfo oggetto, un NumberFormatInfo oggetto o un'implementazione personalizzata IFormatProvider che restituisce un NumberFormatInfo oggetto.provider must be a CultureInfo object, a NumberFormatInfo object, or a custom IFormatProvider implementation that returns a NumberFormatInfo object. Tuttavia, poiché il ChangeType(Object, TypeCode, IFormatProvider) metodo esegue la conversione usando l'identificatore di formato "G" predefinito, il provider parametro non ha alcun effetto se value o il tipo di destinazione è un Unsigned Integer.However, because the ChangeType(Object, TypeCode, IFormatProvider) method performs the conversion using the default "G" format specifier, the provider parameter has no effect if value or the target type is an unsigned integer. Se provider è null , CultureInfo viene utilizzato l'oggetto che rappresenta le impostazioni cultura del thread corrente.If provider is null, the CultureInfo object that represents the current thread culture is used.

• Conversione da un DateTime valore a una stringa o da una stringa a un DateTime valore.Conversion from a DateTime value to a string, or from a string to a DateTime value. provider deve essere un CultureInfo DateTimeFormatInfo oggetto o.provider must be a CultureInfo or DateTimeFormatInfo object. Se provider è null , CultureInfo viene utilizzato l'oggetto che rappresenta le impostazioni cultura del thread corrente.If provider is null, the CultureInfo object that represents the current thread culture is used.

Se value è un tipo definito dall'applicazione, la relativa IConvertible implementazione può utilizzare il provider parametro.If value is an application-defined type, its IConvertible implementation may use the provider parameter.

Note per i chiamanti

Il ChangeType(Object, Type, IFormatProvider) metodo può convertire un valore di enumerazione in un altro tipo.The ChangeType(Object, Type, IFormatProvider) method can convert an enumeration value to another type. Tuttavia, non è in grado di convertire un altro tipo in un valore di enumerazione, anche se il tipo di origine è il tipo sottostante dell'enumerazione.However, it cannot convert another type to an enumeration value, even if the source type is the underlying type of the enumeration. Per convertire un tipo in un valore di enumerazione, usare un operatore di cast (in C#) o una funzione di conversione (in Visual Basic).To convert a type to an enumeration value, use a casting operator (in C#) or a conversion function (in Visual Basic). Nell'esempio seguente viene illustrata la conversione da e verso un valore di enumerazione continente .The following example illustrates the conversion to and from a Continent enumeration value.

::: Code Language = "CSharp" Source = "~/Samples/Snippets/CSharp/VS_Snippets_CLR_System/System.Convert.ChangeType/CS/changetype_enum2. cs" Interactive = "try-dotnet" ID = "Snippet5":::::: Code Language = "VB" Source = "~/Samples/Snippets/VisualBasic/VS_Snippets_CLR_System/System.Convert.ChangeType/VB/changetype_enum2. vb" ID = "Snippet5"::::::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.convert.changetype/cs/changetype_enum2.cs" interactive="try-dotnet" id="Snippet5"::: :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.convert.changetype/vb/changetype_enum2.vb" id="Snippet5":::

Il ChangeType(Object, Type, IFormatProvider) metodo può convertire un tipo nullable in un altro tipo.The ChangeType(Object, Type, IFormatProvider) method can convert a nullable type to another type. Tuttavia, non può convertire un altro tipo in un valore di un tipo nullable, anche se conversionType è il tipo sottostante di Nullable<T> .However, it cannot convert another type to a value of a nullable type, even if conversionType is the underlying type of the Nullable<T>. Per eseguire la conversione, è possibile usare un operatore di cast (in C#) o una funzione di conversione (in Visual Basic).To perform the conversion, you can use a casting operator (in C#) or a conversion function (in Visual Basic). Nell'esempio seguente viene illustrata la conversione da e verso un tipo Nullable.The following example illustrates the conversion to and from a nullable type.

::: Code Language = "CSharp" Source = "~/Samples/Snippets/CSharp/VS_Snippets_CLR_System/System.Convert.ChangeType/CS/changetype_nullable_1. cs" Interactive = "try-dotnet" ID = "Snippet8":::::: Code Language = "VB" Source = "~/Samples/Snippets/VisualBasic/VS_Snippets_CLR_System/System.Convert.ChangeType/VB/changetype_nullable_1. vb" ID = "Snippet8"::::::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.convert.changetype/cs/changetype_nullable_1.cs" interactive="try-dotnet" id="Snippet8"::: :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.convert.changetype/vb/changetype_nullable_1.vb" id="Snippet8":::

public:
 static System::Object ^ ChangeType(System::Object ^ value, TypeCode typeCode, IFormatProvider ^ provider);

public static object ChangeType (object value, TypeCode typeCode, IFormatProvider provider);

static member ChangeType : obj * TypeCode * IFormatProvider -> obj

Public Shared Function ChangeType (value As Object, typeCode As TypeCode, provider As IFormatProvider) As Object

Parametri

Restituisce

Object

Oggetto il cui tipo sottostante è typeCode e il cui valore è equivalente a value.An object whose underlying type is typeCode and whose value is equivalent to value.

-oppure--or-

Riferimento Null (Nothing in Visual Basic), se value è null e typeCode è Empty, String o Object.A null reference (Nothing in Visual Basic), if value is null and typeCode is Empty, String, or Object.

Eccezioni

Esempio

Nell'esempio seguente viene definito un provider di formato personalizzato denominato InterceptProvider che indica quando GetFormat viene chiamato il metodo e restituisce un NumberFormatInfo oggetto per le impostazioni cultura fr-FR e un DateTimeFormatInfo oggetto per le impostazioni cultura en-US.The following example defines a custom format provider named InterceptProvider that indicates when its GetFormat method is called and returns a NumberFormatInfo for the fr-FR culture and a DateTimeFormatInfo object for the en-US culture. Questo provider di formato viene usato in tutte le chiamate al ChangeType(Object, TypeCode, IFormatProvider) metodo.This format provider is used in all calls to the ChangeType(Object, TypeCode, IFormatProvider) method. Nell'esempio viene quindi creata una matrice con un oggetto Double e un DateTime valore che effettua chiamate ripetute a ChangeType(Object, TypeCode, IFormatProvider) con ogni valore e ogni membro dell' TypeCode enumerazione.The example then creates an array with a Double and a DateTime value and makes repeated calls to ChangeType(Object, TypeCode, IFormatProvider) with each value and each member of the TypeCode enumeration. L'esempio illustra quando il metodo usa il IFormatProvider parametro e illustra anche l'uso del provider parametro per eseguire la formattazione dipendente dalle impostazioni cultura.The example illustrates when the method uses the IFormatProvider parameter and also illustrates the use of the provider parameter to perform culture-sensitive formatting.

using namespace System;
using namespace System::Globalization;

ref class InterceptProvider : IFormatProvider
{
public: 
   virtual Object^ GetFormat(Type^ formatType) 
   {
      CultureInfo^ culture;
      if (formatType == NumberFormatInfo::typeid) {
         Console::WriteLine("   Returning a fr-FR numeric format provider.");
         
         culture = gcnew CultureInfo("fr-FR");
         return culture->NumberFormat;
      }  
      else if (formatType == DateTimeFormatInfo::typeid) {
         Console::WriteLine("   Returning an en-US date/time format provider.");
         culture = gcnew CultureInfo("en-US");
         return culture->DateTimeFormat;
      }
      else {
         Console::WriteLine("   Requesting a format provider of {0}.", formatType->Name);
         return nullptr;
      }
   }
};

void main()
{
   array<Object^>^ values = gcnew array<Object^> { 103.5, gcnew DateTime(2010, 12, 26, 14, 34, 0) };
   IFormatProvider^ provider = gcnew InterceptProvider();
      
   // Convert value to each of the types represented in TypeCode enum.
   for each (Object^ value in values)
   {
      // Iterate types in TypeCode enum.
      for each (TypeCode enumType in (array<TypeCode>^) Enum::GetValues(TypeCode::typeid))
      {         
         if (enumType == TypeCode::DBNull || enumType == TypeCode::Empty) continue;
            
         try {
            Console::WriteLine("{0} ({1}) --> {2} ({3}).", 
                              value, value->GetType()->Name,
                              Convert::ChangeType(value, enumType, provider),
                              enumType.ToString());
         }
         catch (InvalidCastException^ e) {
            Console::WriteLine("Cannot convert a {0} to a {1}",
                              value->GetType()->Name, enumType.ToString());
         }                     
         catch (OverflowException^ e) {
            Console::WriteLine("Overflow: {0} is out of the range of a {1}",
                              value, enumType.ToString());
         }
      }
      Console::WriteLine();
   }
}
// The example displays the following output:
//    103.5 (Double) --> 103.5 (Object).
//    103.5 (Double) --> True (Boolean).
//    Cannot convert a Double to a Char
//    103.5 (Double) --> 104 (SByte).
//    103.5 (Double) --> 104 (Byte).
//    103.5 (Double) --> 104 (Int16).
//    103.5 (Double) --> 104 (UInt16).
//    103.5 (Double) --> 104 (Int32).
//    103.5 (Double) --> 104 (UInt32).
//    103.5 (Double) --> 104 (Int64).
//    103.5 (Double) --> 104 (UInt64).
//    103.5 (Double) --> 103.5 (Single).
//    103.5 (Double) --> 103.5 (Double).
//    103.5 (Double) --> 103.5 (Decimal).
//    Cannot convert a Double to a DateTime
//       Returning a fr-FR numeric format provider.
//    103.5 (Double) --> 103,5 (String).
//    
//    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (Object).
//    Cannot convert a DateTime to a Boolean
//    Cannot convert a DateTime to a Char
//    Cannot convert a DateTime to a SByte
//    Cannot convert a DateTime to a Byte
//    Cannot convert a DateTime to a Int16
//    Cannot convert a DateTime to a UInt16
//    Cannot convert a DateTime to a Int32
//    Cannot convert a DateTime to a UInt32
//    Cannot convert a DateTime to a Int64
//    Cannot convert a DateTime to a UInt64
//    Cannot convert a DateTime to a Single
//    Cannot convert a DateTime to a Double
//    Cannot convert a DateTime to a Decimal
//    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (DateTime).
//       Returning an en-US date/time format provider.
//    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (String).

using System;
using System.Globalization;

public class InterceptProvider : IFormatProvider
{
   public object GetFormat(Type formatType)
   {
      if (formatType == typeof(NumberFormatInfo)) {
         Console.WriteLine("   Returning a fr-FR numeric format provider.");
         return new System.Globalization.CultureInfo("fr-FR").NumberFormat;
      }
      else if (formatType == typeof(DateTimeFormatInfo)) {
         Console.WriteLine("   Returning an en-US date/time format provider.");
         return new System.Globalization.CultureInfo("en-US").DateTimeFormat;
      }
      else {
         Console.WriteLine("   Requesting a format provider of {0}.", formatType.Name);
         return null;
      }
   }
}

public class Example
{
   public static void Main()
   {
      object[] values = { 103.5d, new DateTime(2010, 12, 26, 14, 34, 0) };
      IFormatProvider provider = new InterceptProvider();

      // Convert value to each of the types represented in TypeCode enum.
      foreach (object value in values)
      {
         // Iterate types in TypeCode enum.
         foreach (TypeCode enumType in ((TypeCode[]) Enum.GetValues(typeof(TypeCode))))
         {
            if (enumType == TypeCode.DBNull || enumType == TypeCode.Empty) continue;

            try {
               Console.WriteLine("{0} ({1}) --> {2} ({3}).",
                                 value, value.GetType().Name,
                                 Convert.ChangeType(value, enumType, provider),
                                 enumType.ToString());
            }
            catch (InvalidCastException) {
               Console.WriteLine("Cannot convert a {0} to a {1}",
                                 value.GetType().Name, enumType.ToString());
            }
            catch (OverflowException) {
               Console.WriteLine("Overflow: {0} is out of the range of a {1}",
                                 value, enumType.ToString());
            }
         }
         Console.WriteLine();
      }
   }
}
// The example displays the following output:
//    103.5 (Double) --> 103.5 (Object).
//    103.5 (Double) --> True (Boolean).
//    Cannot convert a Double to a Char
//    103.5 (Double) --> 104 (SByte).
//    103.5 (Double) --> 104 (Byte).
//    103.5 (Double) --> 104 (Int16).
//    103.5 (Double) --> 104 (UInt16).
//    103.5 (Double) --> 104 (Int32).
//    103.5 (Double) --> 104 (UInt32).
//    103.5 (Double) --> 104 (Int64).
//    103.5 (Double) --> 104 (UInt64).
//    103.5 (Double) --> 103.5 (Single).
//    103.5 (Double) --> 103.5 (Double).
//    103.5 (Double) --> 103.5 (Decimal).
//    Cannot convert a Double to a DateTime
//       Returning a fr-FR numeric format provider.
//    103.5 (Double) --> 103,5 (String).
//
//    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (Object).
//    Cannot convert a DateTime to a Boolean
//    Cannot convert a DateTime to a Char
//    Cannot convert a DateTime to a SByte
//    Cannot convert a DateTime to a Byte
//    Cannot convert a DateTime to a Int16
//    Cannot convert a DateTime to a UInt16
//    Cannot convert a DateTime to a Int32
//    Cannot convert a DateTime to a UInt32
//    Cannot convert a DateTime to a Int64
//    Cannot convert a DateTime to a UInt64
//    Cannot convert a DateTime to a Single
//    Cannot convert a DateTime to a Double
//    Cannot convert a DateTime to a Decimal
//    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (DateTime).
//       Returning an en-US date/time format provider.
//    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (String).

Imports System.Globalization

Public Class InterceptProvider : Implements IFormatProvider
   Public Function GetFormat(formatType As Type) As Object _
          Implements IFormatProvider.GetFormat
      If formatType.Equals(GetType(NumberFormatInfo)) Then
         Console.WriteLine("   Returning a fr-FR numeric format provider.")
         Return New CultureInfo("fr-FR").NumberFormat
      ElseIf formatType.Equals(GetType(DateTimeFormatInfo)) Then
         Console.WriteLine("   Returning an en-US date/time format provider.")
         Return New CultureInfo("en-US").DateTimeFormat
      Else
         Console.WriteLine("   Requesting a format provider of {0}.", formatType.Name)
         Return Nothing
      End If
   End Function
End Class

Module Example
   Public Sub Main()
      Dim values() As Object = { 103.5r, #12/26/2010 2:34PM# }
      Dim provider As New InterceptProvider()
      
      ' Convert value to each of the types represented in TypeCode enum.
      For Each value As Object In values
         ' Iterate types in TypeCode enum.
         For Each enumType As TypeCode In DirectCast([Enum].GetValues(GetType(TypeCode)), TypeCode())         
            If enumType = TypeCode.DbNull Or enumType = TypeCode.Empty Then Continue For
            
            Try
               Console.WriteLine("{0} ({1}) --> {2} ({3}).", _
                                 value, value.GetType().Name, _
                                 Convert.ChangeType(value, enumType, provider), _
                                 enumType.ToString())
            Catch e As InvalidCastException
               Console.WriteLine("Cannot convert a {0} to a {1}", _
                                 value.GetType().Name, enumType.ToString())
            Catch e As OverflowException
               Console.WriteLine("Overflow: {0} is out of the range of a {1}", _
                                 value, enumType.ToString())
            End Try
         Next
         Console.WriteLine()
      Next
   End Sub
End Module
' The example displays the following output:
'    103.5 (Double) --> 103.5 (Object).
'    103.5 (Double) --> True (Boolean).
'    Cannot convert a Double to a Char
'    103.5 (Double) --> 104 (SByte).
'    103.5 (Double) --> 104 (Byte).
'    103.5 (Double) --> 104 (Int16).
'    103.5 (Double) --> 104 (UInt16).
'    103.5 (Double) --> 104 (Int32).
'    103.5 (Double) --> 104 (UInt32).
'    103.5 (Double) --> 104 (Int64).
'    103.5 (Double) --> 104 (UInt64).
'    103.5 (Double) --> 103.5 (Single).
'    103.5 (Double) --> 103.5 (Double).
'    103.5 (Double) --> 103.5 (Decimal).
'    Cannot convert a Double to a DateTime
'       Returning a fr-FR numeric format provider.
'    103.5 (Double) --> 103,5 (String).
'    
'    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (Object).
'    Cannot convert a DateTime to a Boolean
'    Cannot convert a DateTime to a Char
'    Cannot convert a DateTime to a SByte
'    Cannot convert a DateTime to a Byte
'    Cannot convert a DateTime to a Int16
'    Cannot convert a DateTime to a UInt16
'    Cannot convert a DateTime to a Int32
'    Cannot convert a DateTime to a UInt32
'    Cannot convert a DateTime to a Int64
'    Cannot convert a DateTime to a UInt64
'    Cannot convert a DateTime to a Single
'    Cannot convert a DateTime to a Double
'    Cannot convert a DateTime to a Decimal
'    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (DateTime).
'       Returning an en-US date/time format provider.
'    12/26/2010 2:34:00 PM (DateTime) --> 12/26/2010 2:34:00 PM (String).

Commenti

ChangeType(Object, TypeCode, IFormatProvider) è un metodo di conversione di utilizzo generico che converte l'oggetto specificato da value in un tipo predefinito specificato da typeCode .ChangeType(Object, TypeCode, IFormatProvider) is a general-purpose conversion method that converts the object specified by value to a predefined type specified by typeCode. Il value parametro può essere un oggetto di qualsiasi tipo.The value parameter can be an object of any type. Affinché la conversione abbia esito positivo, value deve implementare l' IConvertible interfaccia, perché il metodo esegue semplicemente il wrapping di una chiamata a un IConvertible metodo appropriato.For the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. Il metodo richiede anche che la conversione value di typeCode sia supportata.The method also requires that conversion of value to typeCode be supported.

Il ChangeType(Object, TypeCode, IFormatProvider) metodo non supporta la conversione di value in un tipo personalizzato.The ChangeType(Object, TypeCode, IFormatProvider) method does not support the conversion of value to a custom type. Per eseguire tale conversione, chiamare il ChangeType(Object, Type, IFormatProvider) metodo.To perform such a conversion, call the ChangeType(Object, Type, IFormatProvider) method.

Il provider parametro è un' IFormatProvider implementazione di che fornisce informazioni sulla formattazione per la conversione.The provider parameter is an IFormatProvider implementation that supplies formatting information for the conversion. L'utilizzo di questo parametro dipende dall' IConvertible implementazione sottostante.Whether and how this parameter is used depends on the underlying IConvertible implementation. Se value è un tipo di dati di base, provider viene utilizzato solo per le conversioni seguenti.If value is a base data type, provider is used only for the following conversions. Se un null IFormatProvider argomento viene passato a questi metodi, CultureInfo viene utilizzato l'oggetto che rappresenta le impostazioni cultura del thread corrente.If a nullIFormatProvider argument is passed to these methods, the CultureInfo object that represents the current thread culture is used.

• Conversione da un numero a una stringa o da una stringa a un numero.Conversion from a number to a string, or from a string to a number. provider deve essere un CultureInfo oggetto, un NumberFormatInfo oggetto o un'implementazione personalizzata IFormatProvider che restituisce un NumberFormatInfo oggetto.provider must be a CultureInfo object, a NumberFormatInfo object, or a custom IFormatProvider implementation that returns a NumberFormatInfo object. Tuttavia, poiché il ChangeType(Object, TypeCode, IFormatProvider) metodo esegue la conversione usando l'identificatore di formato "G" predefinito, il provider parametro non ha alcun effetto se value o il tipo di destinazione è un Unsigned Integer.However, because the ChangeType(Object, TypeCode, IFormatProvider) method performs the conversion using the default "G" format specifier, the provider parameter has no effect if value or the target type is an unsigned integer.

• Conversione da un DateTime valore a una stringa o da una stringa a un DateTime valore.Conversion from a DateTime value to a string, or from a string to a DateTime value. provider deve essere un CultureInfo DateTimeFormatInfo oggetto o.provider must be a CultureInfo or DateTimeFormatInfo object.

Se value è un tipo definito dall'applicazione, la relativa IConvertible implementazione può utilizzare il provider parametro.If value is an application-defined type, its IConvertible implementation may use the provider parameter.