Convert.ChangeType 方法

定義

傳回指定之類型的物件,此物件的值與指定的物件相等。Returns an object of a specified type whose value is equivalent to a specified object.

多載

ChangeType(Object, Type)

傳回指定之類型的物件,此物件的值與指定的物件相等。Returns an object of the specified type and whose value is equivalent to the specified object.

ChangeType(Object, TypeCode)

傳回物件,該物件屬於指定的類型,且其值等於指定的物件。Returns an object of the specified type whose value is equivalent to the specified object.

ChangeType(Object, Type, IFormatProvider)

傳回物件,該物件屬於指定的類型,且其值等於指定的物件。Returns an object of the specified type whose value is equivalent to the specified object. 參數提供特定文化特性格式資訊。A parameter supplies culture-specific formatting information.

ChangeType(Object, TypeCode, IFormatProvider)

傳回物件,該物件屬於指定的類型,且其值等於指定的物件。Returns an object of the specified type whose value is equivalent to the specified object. 參數提供特定文化特性格式資訊。A parameter supplies culture-specific formatting information.

ChangeType(Object, Type)

傳回指定之類型的物件,此物件的值與指定的物件相等。Returns an object of the specified type and whose value is equivalent to the specified object.

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

參數

value
Object

實作 IConvertible 介面的物件。An object that implements the IConvertible interface.

conversionType
Type

要傳回的物件類型。The type of object to return.

傳回

Object

類型為 conversionType 且值與 value 相等的物件。An object whose type is conversionType and whose value is equivalent to value.

-或--or-

如果 Nothingvaluenull 不是實值類型,則為 null 參考 (在 Visual Basic 中為 conversionType)。A null reference (Nothing in Visual Basic), if value is null and conversionType is not a value type.

例外狀況

不支援此轉換。This conversion is not supported.

-或--or-

valuenull,且 conversionType 是實值類型。value is null and conversionType is a value type.

-或--or-

value 未實作 IConvertible 介面。value does not implement the IConvertible interface.

value 不是 conversionType 可辨識的格式。value is not in a format recognized by conversionType.

value 代表超出 conversionType範圍的數字。value represents a number that is out of the range of conversionType.

conversionTypenullconversionType is null.

範例

在下列程式碼中,說明了如何使用 ChangeType 方法。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

備註

ChangeType 是一般用途的轉換方法,會將指定的物件轉換 valueconversionTypeChangeType is a general-purpose conversion method that converts the object specified by value to conversionType. value參數可以是任何類型的物件, conversionType 也可以是 Type 代表任何基底或自訂類型的物件。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. 為了讓轉換成功, value 必須執行 IConvertible 介面,因為方法只會包裝對適當方法的呼叫 IConvertibleFor the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. 方法需要支援的轉換 value conversionTypeThe method requires that conversion of value to conversionType be supported.

這個方法會使用目前線程的文化特性進行轉換。This method uses the current thread's culture for the conversion.

給呼叫者的注意事項

ChangeType(Object, Type)方法可以將列舉值轉換成另一種類型。The ChangeType(Object, Type) method can convert an enumeration value to another type. 不過,它無法將另一個類型轉換成列舉值,即使來源類型是列舉的基礎類型。However, it cannot convert another type to an enumeration value, even if the source type is the underlying type of the enumeration. 若要將類型轉換為列舉值,請使用 c # ) 中的轉型運算子 (或 Visual Basic) 中 (的轉換函數。To convert a type to an enumeration value, use a casting operator (in C#) or a conversion function (in Visual Basic). 下列範例說明如何在 大陸 列舉值之間進行轉換。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 = "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":::

ChangeType(Object, Type)方法可以將可為 null 的型別轉換成另一種類型。The ChangeType(Object, Type) method can convert a nullable type to another type. 但是,它無法將另一個型別轉換成可為 null 型別的值,即使 conversionType 是的基礎型別也是一樣 Nullable<T> 。若要執行轉換,您可以使用 c # 中的轉型運算子 () 或 Visual Basic) 中 (的轉換函數。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). 下列範例說明如何從可為 null 的型別進行轉換。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 = "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":::

適用於

ChangeType(Object, TypeCode)

傳回物件,該物件屬於指定的類型,且其值等於指定的物件。Returns an object of the specified type whose value is equivalent to the specified object.

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

參數

value
Object

實作 IConvertible 介面的物件。An object that implements the IConvertible interface.

typeCode
TypeCode

要傳回的物件類型。The type of object to return.

傳回

Object

基礎類型為 typeCode 且值與 value 相等的物件。An object whose underlying type is typeCode and whose value is equivalent to value.

-或--or-

如果 Nothingvalue,而且 nulltypeCodeEmptyString,則為 null 參考 (在 Visual Basic 中為 Object)。A null reference (Nothing in Visual Basic), if value is null and typeCode is Empty, String, or Object.

例外狀況

不支援此轉換。This conversion is not supported.

-或--or-

valuenull,而且 typeCode 會指定實值型別。value is null and typeCode specifies a value type.

-或--or-

value 未實作 IConvertible 介面。value does not implement the IConvertible interface.

value 不是 typeCode 類型可辨識的格式。value is not in a format recognized by the typeCode type.

value 代表超出 typeCode 類型範圍的數字。value represents a number that is out of the range of the typeCode type.

typeCode 無效。typeCode is invalid.

範例

下列範例說明如何使用 ChangeType(Object, TypeCode) 方法,將變更 Object 為參數所指定的型別 TypeCode (如果可能的話)。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

備註

ChangeType(Object, TypeCode) 是一般用途的轉換方法,它會將指定的物件轉換 value 為所指定的預先定義型別 typeCodeChangeType(Object, TypeCode) is a general-purpose conversion method that converts the object specified by value to a predefined type specified by typeCode. value參數可以是任何類型的物件。The value parameter can be an object of any type. 為了讓轉換成功, value 必須執行 IConvertible 介面,因為方法只會包裝對適當方法的呼叫 IConvertibleFor the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. 方法也需要支援的轉換 value typeCodeThe method also requires that conversion of value to typeCode be supported.

ChangeType(Object, TypeCode)方法不支援將轉換 value 為自訂類型。The ChangeType(Object, TypeCode) method does not support the conversion of value to a custom type. 若要執行這類轉換,請呼叫 ChangeType(Object, Type) 方法。To perform such a conversion, call the ChangeType(Object, Type) method.

適用於

ChangeType(Object, Type, IFormatProvider)

傳回物件,該物件屬於指定的類型,且其值等於指定的物件。Returns an object of the specified type whose value is equivalent to the specified object. 參數提供特定文化特性格式資訊。A parameter supplies culture-specific formatting information.

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

參數

value
Object

實作 IConvertible 介面的物件。An object that implements the IConvertible interface.

conversionType
Type

要傳回的物件類型。The type of object to return.

provider
IFormatProvider

物件,提供特定文化特性格式資訊。An object that supplies culture-specific formatting information.

傳回

Object

類型為 conversionType 且值與 value 相等的物件。An object whose type is conversionType and whose value is equivalent to value.

-或--or-

如果 valueTypevalue 相等,則為 conversionTypevalue, if the Type of value and conversionType are equal.

-或--or-

如果 Nothingvaluenull 不是實值類型,則為 null 參考 (在 Visual Basic 中為 conversionType)。A null reference (Nothing in Visual Basic), if value is null and conversionType is not a value type.

例外狀況

不支援此轉換。This conversion is not supported.

-或--or-

valuenull,且 conversionType 是實值類型。value is null and conversionType is a value type.

-或--or-

value 未實作 IConvertible 介面。value does not implement the IConvertible interface.

value 格式不是 provider 所辨識的 conversionTypevalue is not in a format for conversionType recognized by provider.

value 代表超出 conversionType範圍的數字。value represents a number that is out of the range of conversionType.

conversionTypenullconversionType is null.

範例

下列範例定義一個實作 Temperature 介面的 IConvertible 類別。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

下列範例會建立類別的實例 Temperature ,並呼叫方法,將 ChangeType(Object, Type, IFormatProvider) 它轉換為 .net 和所支援的基本數數值型別 StringThe 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. 它說明方法會 ChangeType 包裝對來源型別執行的呼叫 IConvertibleIt 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.

備註

ChangeType 是一般用途的轉換方法,會將指定的物件轉換 valueconversionTypeChangeType is a general-purpose conversion method that converts the object specified by value to conversionType. value參數可以是任何類型的物件, conversionType 也可以是 Type 代表任何基底或自訂類型的物件。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. 為了讓轉換成功, value 必須執行 IConvertible 介面,因為方法只會包裝對適當方法的呼叫 IConvertibleFor the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. 方法需要支援的轉換 value conversionTypeThe method requires that conversion of value to conversionType be supported.

provider參數是 IFormatProvider 提供轉換格式資訊的實作為。The provider parameter is an IFormatProvider implementation that supplies formatting information for the conversion. 此參數的使用方式取決於基礎 IConvertible 執行。Whether and how this parameter is used depends on the underlying IConvertible implementation. 如果 value 是基底資料類型, provider 只會用於下列轉換:If value is a base data type, provider is used only for the following conversions:

如果 value 是應用程式定義型別,其 IConvertible 實作為可能會使用 provider 參數。If value is an application-defined type, its IConvertible implementation may use the provider parameter.

給呼叫者的注意事項

ChangeType(Object, Type, IFormatProvider)方法可以將列舉值轉換成另一種類型。The ChangeType(Object, Type, IFormatProvider) method can convert an enumeration value to another type. 不過,它無法將另一個類型轉換成列舉值,即使來源類型是列舉的基礎類型。However, it cannot convert another type to an enumeration value, even if the source type is the underlying type of the enumeration. 若要將類型轉換為列舉值,請使用 c # ) 中的轉型運算子 (或 Visual Basic) 中 (的轉換函數。To convert a type to an enumeration value, use a casting operator (in C#) or a conversion function (in Visual Basic). 下列範例說明如何在 大陸 列舉值之間進行轉換。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 = "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":::

ChangeType(Object, Type, IFormatProvider)方法可以將可為 null 的型別轉換成另一種類型。The ChangeType(Object, Type, IFormatProvider) method can convert a nullable type to another type. 但是,它無法將另一個型別轉換成可為 null 型別的值,即使 conversionType 是的基礎型別也是一樣 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>. 若要執行轉換,您可以使用 c # 中的轉型運算子 () 或 Visual Basic) 中 (的轉換函數。To perform the conversion, you can use a casting operator (in C#) or a conversion function (in Visual Basic). 下列範例說明如何從可為 null 的型別進行轉換。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 = "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":::

適用於

ChangeType(Object, TypeCode, IFormatProvider)

傳回物件,該物件屬於指定的類型,且其值等於指定的物件。Returns an object of the specified type whose value is equivalent to the specified object. 參數提供特定文化特性格式資訊。A parameter supplies culture-specific formatting information.

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

參數

value
Object

實作 IConvertible 介面的物件。An object that implements the IConvertible interface.

typeCode
TypeCode

要傳回的物件類型。The type of object to return.

provider
IFormatProvider

物件,提供特定文化特性格式資訊。An object that supplies culture-specific formatting information.

傳回

Object

基礎類型為 typeCode 且值與 value 相等的物件。An object whose underlying type is typeCode and whose value is equivalent to value.

-或--or-

如果 Nothingvalue,而且 nulltypeCodeEmptyString,則為 null 參考 (在 Visual Basic 中為 Object)。A null reference (Nothing in Visual Basic), if value is null and typeCode is Empty, String, or Object.

例外狀況

不支援此轉換。This conversion is not supported.

-或--or-

valuenull,而且 typeCode 會指定實值型別。value is null and typeCode specifies a value type.

-或--or-

value 未實作 IConvertible 介面。value does not implement the IConvertible interface.

value 格式不是 provider 所辨識的 typeCode 類型。value is not in a format for the typeCode type recognized by provider.

value 代表超出 typeCode 類型範圍的數字。value represents a number that is out of the range of the typeCode type.

typeCode 無效。typeCode is invalid.

範例

下列範例會定義名為的自訂格式提供者 InterceptProvider ,這個提供者會指出呼叫它的 GetFormat 方法,並傳回 fr-fr 文化特性的,以及 NumberFormatInfo en-us 文化特性的 DateTimeFormatInfo 物件。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. 此格式提供者用於方法的所有呼叫中 ChangeType(Object, TypeCode, IFormatProvider)This format provider is used in all calls to the ChangeType(Object, TypeCode, IFormatProvider) method. 然後,此範例會建立具有 Double 和值的陣列 DateTime ,並 ChangeType(Object, TypeCode, IFormatProvider) 使用每個值和列舉的每個成員重複呼叫 TypeCodeThe 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. 此範例說明當方法使用參數時 IFormatProvider ,也會說明 provider 如何使用參數來執行區分文化特性的格式設定。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).

備註

ChangeType(Object, TypeCode, IFormatProvider) 是一般用途的轉換方法,它會將指定的物件轉換 value 為所指定的預先定義型別 typeCodeChangeType(Object, TypeCode, IFormatProvider) is a general-purpose conversion method that converts the object specified by value to a predefined type specified by typeCode. value參數可以是任何類型的物件。The value parameter can be an object of any type. 為了讓轉換成功, value 必須執行 IConvertible 介面,因為方法只會包裝對適當方法的呼叫 IConvertibleFor the conversion to succeed, value must implement the IConvertible interface, because the method simply wraps a call to an appropriate IConvertible method. 方法也需要支援的轉換 value typeCodeThe method also requires that conversion of value to typeCode be supported.

ChangeType(Object, TypeCode, IFormatProvider)方法不支援將轉換 value 為自訂類型。The ChangeType(Object, TypeCode, IFormatProvider) method does not support the conversion of value to a custom type. 若要執行這類轉換,請呼叫 ChangeType(Object, Type, IFormatProvider) 方法。To perform such a conversion, call the ChangeType(Object, Type, IFormatProvider) method.

provider參數是 IFormatProvider 提供轉換格式資訊的實作為。The provider parameter is an IFormatProvider implementation that supplies formatting information for the conversion. 此參數的使用方式取決於基礎 IConvertible 執行。Whether and how this parameter is used depends on the underlying IConvertible implementation. 如果 value 是基底資料類型, provider 只會用於下列轉換。If value is a base data type, provider is used only for the following conversions. 如果將 null IFormatProvider 引數傳遞至這些方法,則 CultureInfo 會使用代表目前線程文化特性的物件。If a nullIFormatProvider argument is passed to these methods, the CultureInfo object that represents the current thread culture is used.

如果 value 是應用程式定義型別,其 IConvertible 實作為可能會使用 provider 參數。If value is an application-defined type, its IConvertible implementation may use the provider parameter.

適用於