.NET Framework Class Library
ValueConversionAttribute Class

Represents an attribute that allows the author of a value converter to specify the data types involved in the implementation of the converter.

Inheritance Hierarchy
SystemObject
   SystemAttribute
    System.Windows.DataValueConversionAttribute

Namespace:   System.Windows.Data
Assembly:  PresentationFramework (in PresentationFramework.dll)
Syntax
<[%$TOPIC/ms613768_en-us_VS_110_2_0_0_0_0%]([%$TOPIC/ms613768_en-us_VS_110_2_0_0_0_1%].Class, AllowMultiple := True)> _
Public NotInheritable Class ValueConversionAttribute _
	Inherits [%$TOPIC/ms613768_en-us_VS_110_2_0_0_0_2%]
[[%$TOPIC/ms613768_en-us_VS_110_2_0_1_0_0%]([%$TOPIC/ms613768_en-us_VS_110_2_0_1_0_1%].Class, AllowMultiple = true)]
public sealed class ValueConversionAttribute : [%$TOPIC/ms613768_en-us_VS_110_2_0_1_0_2%]
[[%$TOPIC/ms613768_en-us_VS_110_2_0_2_0_0%]([%$TOPIC/ms613768_en-us_VS_110_2_0_2_0_1%]::Class, AllowMultiple = true)]
public ref class ValueConversionAttribute sealed : public [%$TOPIC/ms613768_en-us_VS_110_2_0_2_0_2%]
[<[%$TOPIC/ms613768_en-us_VS_110_2_0_3_0_0%]>]
[<[%$TOPIC/ms613768_en-us_VS_110_2_0_3_0_1%]([%$TOPIC/ms613768_en-us_VS_110_2_0_3_0_2%].Class, AllowMultiple = true)>]
type ValueConversionAttribute =  
    class 
        inherit [%$TOPIC/ms613768_en-us_VS_110_2_0_3_0_3%] 
    end

The ValueConversionAttribute type exposes the following members.

Constructors
  NameDescription
Public method ValueConversionAttributeInitializes a new instance of the ValueConversionAttribute class with the specified source type and target type.
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Properties
  NameDescription
Public property ParameterTypeGets and sets the type of the optional value converter parameter object.
Public property SourceTypeGets the type this converter converts.
Public property TargetTypeGets the type this converter converts to.
Public property TypeIdGets the unique identifier of this ValueConversionAttribute instance. (Overrides AttributeTypeId.)
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Methods
  NameDescription
Public method EqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Public method GetHashCodeReturns the hash code for this instance of ValueConversionAttribute. (Overrides AttributeGetHashCode.)
Public method GetTypeGets the Type of the current instance. (Inherited from Object.)
Public method IsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public method MatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Public method ToStringReturns a string that represents the current object. (Inherited from Object.)
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Explicit Interface Implementations
  NameDescription
Explicit interface implemetation Private method _AttributeGetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeGetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeGetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeInvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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Examples

This example shows how to apply conversion to data that is used in bindings.

To convert data during binding, you must create a class that implements the IValueConverter interface, which includes the Convert and ConvertBack methods.

The following example shows the implementation of a date converter that converts the date value passed in so that it only shows the year, the month, and the day. When implementing the IValueConverter interface, it is a good practice to decorate the implementation with a ValueConversionAttribute attribute to indicate to development tools the data types involved in the conversion, as in the following example:

Public Class DateConverter
    Implements System.Windows.Data.IValueConverter

    Public Function Convert(ByVal value As Object,
                            ByVal targetType As System.Type,
                            ByVal parameter As Object,
                            ByVal culture As System.Globalization.CultureInfo) _
             As Object Implements System.Windows.Data.IValueConverter.Convert

        Dim DateValue As DateTime = CType(value, DateTime)
        Return DateValue.ToShortDateString

    End Function 

    Public Function ConvertBack(ByVal value As Object,
                                ByVal targetType As System.Type,
                                ByVal parameter As Object,
                                ByVal culture As System.Globalization.CultureInfo) _
            As Object Implements System.Windows.Data.IValueConverter.ConvertBack

        Dim strValue As String = value
        Dim resultDateTime As DateTime
        If DateTime.TryParse(strValue, resultDateTime) Then 
            Return resultDateTime
        End If 
        Return DependencyProperty.UnsetValue

    End Function 
End Class
[ValueConversion(typeof(DateTime), typeof(String))]
public class DateConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DateTime date = (DateTime)value;
        return date.ToShortDateString();
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        string strValue = value as string;
        DateTime resultDateTime;
        if (DateTime.TryParse(strValue, out resultDateTime))
        {
            return resultDateTime;
        }
        return DependencyProperty.UnsetValue;
    }
}

Once you have created a converter, you can add it as a resource in your Extensible Application Markup Language (XAML) file. In the following example, src maps to the namespace in which DateConverter is defined.

<src:DateConverter x:Key="dateConverter"/>

Finally, you can use the converter in your binding using the following syntax. In the following example, the text content of the TextBlock is bound to StartDate, which is a property of an external data source.

<TextBlock Grid.Row="2" Grid.Column="0" Margin="0,0,8,0"
           Name="startDateTitle"
           Style="{StaticResource smallTitleStyle}">Start Date:</TextBlock>
<TextBlock Name="StartDateDTKey" Grid.Row="2" Grid.Column="1" 
    Text="{Binding Path=StartDate, Converter={StaticResource dateConverter}}" 
    Style="{StaticResource textStyleTextBlock}"/>

The style resources referenced in the above example are defined in a resource section not shown in this topic.

Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
Platforms

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.