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IConvertible Interface

Updated: March 2009

Defines methods that convert the value of the implementing reference or value type to a common language runtime type that has an equivalent value.

This API is not CLS-compliant. 

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
<ComVisibleAttribute(True)> _
<CLSCompliantAttribute(False)> _
Public Interface IConvertible
'Usage
Dim instance As IConvertible

This interface provides methods to convert the value of an instance of an implementing type to a common language runtime type that has an equivalent value. The common language runtime types are Boolean, SByte, Byte, Int16, UInt16, Int32, UInt32, Int64, UInt64, Single, Double, Decimal, DateTime, Char, and String.

If there is no meaningful conversion to a common language runtime type, then a particular interface method implementation throws InvalidCastException. For example, if this interface is implemented on a Boolean type, the implementation of the ToDateTime method throws an exception because there is no meaningful DateTime equivalent to a Boolean type.

The common language runtime typically exposes the IConvertible interface through the Convert class. The common language runtime also uses the IConvertible interface internally, in explicit interface implementations, to simplify the code used to support conversions in the Convert class and basic common language runtime types.

In addition to the IConvertible interface, the .NET Framework provides classes called type converters for converting user-defined data types to other data types. For more information, see the Generalized Type Conversion topic.

Notes to Implementers:

If you implement the IConvertible interface, your implementation will be called automatically by the Convert.ChangeType(Object, Type) method if the Object parameter is an instance of your implementing type and the Type parameter is a common language runtime type.

Most conversion methods have a parameter of type IFormatProvider. Most commonly, this parameter represents either the current culture (CultureInfo.CurrentCulture) or a specific culture. Generally, the IConvertible implementations of the base types ignore this parameter. However, you can choose whether to use it in your code.

The following code sample demonstrates an implementation of IConvertible for a Complex number class, allowing it to be cast first as a Double and then calling the static Convert members on that Double.

Imports System

Module Module1

    Public Class Complex
        Implements IConvertible
        Private x As Double 
        Private y As Double 


        Public Sub New(ByVal x As Double, ByVal y As Double)
            Me.x = x
            Me.y = y
        End Sub 'New 


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


        Function ToBoolean(ByVal provider As IFormatProvider) As Boolean Implements IConvertible.ToBoolean
            If x <> 0 Or y <> 0 Then 
                Return True 
            Else 
                Return False 
            End If 
        End Function 

        Function GetDoubleValue() As Double 
            Return Math.Sqrt((x * x + y * y))
        End Function 


        Function ToByte(ByVal provider As IFormatProvider) As Byte Implements IConvertible.ToByte
            Return Convert.ToByte(GetDoubleValue())
        End Function 


        Function ToChar(ByVal provider As IFormatProvider) As Char Implements IConvertible.ToChar
            Return Convert.ToChar(GetDoubleValue())
        End Function 


        Function ToDateTime(ByVal provider As IFormatProvider) As DateTime Implements IConvertible.ToDateTime
            Return Convert.ToDateTime(GetDoubleValue())
        End Function 


        Function ToDecimal(ByVal provider As IFormatProvider) As Decimal Implements IConvertible.ToDecimal
            Return Convert.ToDecimal(GetDoubleValue())
        End Function 


        Function ToDouble(ByVal provider As IFormatProvider) As Double Implements IConvertible.ToDouble
            Return GetDoubleValue()
        End Function 


        Function ToInt16(ByVal provider As IFormatProvider) As Short Implements IConvertible.ToInt16
            Return Convert.ToInt16(GetDoubleValue())
        End Function 


        Function ToInt32(ByVal provider As IFormatProvider) As Integer Implements IConvertible.ToInt32
            Return Convert.ToInt32(GetDoubleValue())
        End Function 


        Function ToInt64(ByVal provider As IFormatProvider) As Long Implements IConvertible.ToInt64
            Return Convert.ToInt64(GetDoubleValue())
        End Function 


        Function ToSByte(ByVal provider As IFormatProvider) As SByte Implements IConvertible.ToSByte
            Return Convert.ToSByte(GetDoubleValue())
        End Function 


        Function ToSingle(ByVal provider As IFormatProvider) As Single Implements IConvertible.ToSingle
            Return Convert.ToSingle(GetDoubleValue())
        End Function 


        Overloads Function ToString(ByVal provider As IFormatProvider) As String Implements IConvertible.ToString
            Return "( " + x.ToString() + " , " + y.ToString() + " )" 
        End Function 


        Function ToType(ByVal conversionType As Type, ByVal provider As IFormatProvider) As Object Implements IConvertible.ToType
            Return Convert.ChangeType(GetDoubleValue(), conversionType)
        End Function 


        Function ToUInt16(ByVal provider As IFormatProvider) As UInt16 Implements IConvertible.ToUInt16
            Return Convert.ToUInt16(GetDoubleValue())
        End Function 


        Function ToUInt32(ByVal provider As IFormatProvider) As UInt32 Implements IConvertible.ToUInt32
            Return Convert.ToUInt32(GetDoubleValue())
        End Function 


        Function ToUInt64(ByVal provider As IFormatProvider) As UInt64 Implements IConvertible.ToUInt64
            Return Convert.ToUInt64(GetDoubleValue())
        End Function 

    End Class 


    Sub Main()
        Dim testComplex As New Complex(4, 7)

        WriteObjectInfo(testComplex)
        WriteObjectInfo(Convert.ToBoolean(testComplex))
        WriteObjectInfo(Convert.ToDecimal(testComplex))
        WriteObjectInfo(Convert.ToString(testComplex))

    End Sub 

    Sub WriteObjectInfo(ByVal testObject As Object)
        Dim typeCode As TypeCode = Type.GetTypeCode(testObject.GetType())

        Select Case typeCode
            Case typeCode.Boolean
                Console.WriteLine("Boolean: {0}", testObject)

            Case typeCode.Double
                Console.WriteLine("Double: {0}", testObject)

            Case Else
                Console.WriteLine("{0}: {1}", typeCode.ToString(), testObject)
        End Select 
    End Sub 

End Module

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

March 2009

Added the Notes for Implementors section.

Information enhancement.

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