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.
Assembly: mscorlib (in mscorlib.dll)
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
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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.