IValueConverter Interface
Microsoft Silverlight will reach end of support after October 2021. Learn more.
Exposes methods that allow modifying the data as it passes through the binding engine.
Namespace: System.Windows.Data
Assembly: System.Windows (in System.Windows.dll)
Syntax
'Declaration
Public Interface IValueConverter
public interface IValueConverter
The IValueConverter type exposes the following members.
Methods
| Name | Description | |
|---|---|---|
.gif "Public method") .gif "Supported by Silverlight for Windows Phone") |
Convert | Modifies the source data before passing it to the target for display in the UI. |
|
ConvertBack | Modifies the target data before passing it to the source object. This method is called only in TwoWay bindings. |
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Remarks
You can create a class that allows you to convert the format of your data between the source and the target by inheriting from IValueConverter. For example, you might want have a list of colors that you store as RGBA values but display them with color names in the UI. By implementing Convert and ConvertBack, you can change the format of the data values as they are passed between the target and source by the binding engine.
Examples
The following example shows how to implement the IValueConverter interface and use the converter when data binding to a collection of object.
<UserControl x:Class="ConverterParameterEx.Page"
xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:ConverterParameterEx"
Width="400" Height="300">
<Grid x:Name="LayoutRoot" Background="White">
<Grid.Resources>
<local:DateFormatter x:Key="FormatConverter" />
</Grid.Resources>
<ComboBox Height="60" Width="200" x:Name="MusicCombo"
ItemsSource="{Binding}">
<ComboBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock FontWeight="Bold" Text="{Binding Path=Name, Mode=OneWay}" />
<TextBlock Text="{Binding Path=Artist, Mode=OneWay}" />
<TextBlock Text="{Binding Path=ReleaseDate, Mode=OneWay,
Converter={StaticResource FormatConverter},
ConverterParameter=\{0:d\}}" />
</StackPanel>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</Grid>
</UserControl>
Imports System.Collections.ObjectModel
Imports System.Windows.Data
Partial Public Class Page
Inherits UserControl
Public MyMusic As New ObservableCollection(Of Recording)()
Public Sub New()
InitializeComponent()
' Add items to the collection.
MyMusic.Add(New Recording("Sheryl Crow", "Detours", New DateTime(2008, 2, 5)))
MyMusic.Add(New Recording("Brandi Carlisle", "The Story", New DateTime(2007, 4, 3)))
MyMusic.Add(New Recording("Patty Griffin", "Children Running Through", New DateTime(2007, 2, 6)))
' Set the data context for the combo box.
MusicCombo.DataContext = MyMusic
End Sub
End Class
' Simple business object.
Public Class Recording
Public Sub New()
End Sub
Public Sub New(ByVal artistName As String, ByVal cdName As String, _
ByVal release As DateTime)
Artist = artistName
Name = cdName
ReleaseDate = release
End Sub
Private artistValue As String
Private nameValue As String
Private releaseDateValue As DateTime
Public Property Artist() As String
Get
Return artistValue
End Get
Set(ByVal value As String)
artistValue = value
End Set
End Property
Public Property Name() As String
Get
Return nameValue
End Get
Set(ByVal value As String)
nameValue = value
End Set
End Property
Public Property ReleaseDate() As DateTime
Get
Return releaseDateValue
End Get
Set(ByVal value As DateTime)
releaseDateValue = value
End Set
End Property
End Class
Public Class DateFormatter
Implements IValueConverter
' This converts the DateTime object to the string to display.
Public Function Convert(ByVal value As Object, ByVal targetType As Type, _
ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object _
Implements IValueConverter.Convert
' Retrieve the format string and use it to format the value.
Dim formatString As String = TryCast(parameter, String)
If Not String.IsNullOrEmpty(formatString) Then
Return String.Format(culture, formatString, value)
End If
' If the format string is null or empty, simply call ToString()
' on the value.
Return value.ToString()
End Function
' No need to implement converting back on a one-way binding.
Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, _
ByVal parameter As Object, _
ByVal culture As System.Globalization.CultureInfo) As Object _
Implements IValueConverter.ConvertBack
Throw New NotImplementedException()
End Function
End Class
using System;
using System.Collections.ObjectModel;
using System.Windows.Controls;
using System.Windows.Data;
namespace ConverterParameterEx
{
public partial class Page : UserControl
{
public ObservableCollection<Recording> MyMusic =
new ObservableCollection<Recording>();
public Page()
{
InitializeComponent();
// Add items to the collection.
MyMusic.Add(new Recording("Chris Sells", "Chris Sells Live",
new DateTime(2008, 2, 5)));
MyMusic.Add(new Recording("Luka Abrus",
"The Road to Redmond", new DateTime(2007, 4, 3)));
MyMusic.Add(new Recording("Jim Hance",
"The Best of Jim Hance", new DateTime(2007, 2, 6)));
// Set the data context for the combo box.
MusicCombo.DataContext = MyMusic;
}
}
// Simple business object.
public class Recording
{
public Recording() { }
public Recording(string artistName, string cdName, DateTime release)
{
Artist = artistName;
Name = cdName;
ReleaseDate = release;
}
public string Artist { get; set; }
public string Name { get; set; }
public DateTime ReleaseDate { get; set; }
}
public class DateFormatter : IValueConverter
{
// This converts the DateTime object to the string to display.
public object Convert(object value, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
// Retrieve the format string and use it to format the value.
string formatString = parameter as string;
if (!string.IsNullOrEmpty(formatString))
{
return string.Format(culture, formatString, value);
}
// If the format string is null or empty, simply call ToString()
// on the value.
return value.ToString();
}
// No need to implement converting back on a one-way binding
public object ConvertBack(object value, Type targetType,
object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.