IValueConverter Interface
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Exposes methods that allow modifying the data as it passes through the binding engine.
Assembly: System.Windows (in System.Windows.dll)
The IValueConverter type exposes the following members.
| Name | Description | |
|---|---|---|
![]() | 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. |
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.
The following example shows how to implement the IValueConverter interface and use the converter when data binding to a collection of object.
<phone:PhoneApplicationPage x:Class="ConverterParameterEx.Page" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone" xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone" xmlns:local="clr-namespace:ConverterParameterEx" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" FontFamily="{StaticResource PhoneFontFamilyNormal}" FontSize="{StaticResource PhoneFontSizeNormal}" Foreground="{StaticResource PhoneForegroundBrush}" mc:Ignorable="d" d:DesignHeight="800" d:DesignWidth="480"> <Grid x:Name="LayoutRoot" Background="Transparent"> <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> </phone:PhoneApplicationPage>
Imports System.Collections.ObjectModel Imports System.Windows.Data Partial Public Class Page Inherits PhoneApplicationPage 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
