IValueConverter interface (Windows)

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Exposes methods that allow the data to be modified as it passes through the binding engine.

Syntax


public interface IValueConverter

Attributes

GuidAttribute("e6f2fef0-0712-487f-b313-f300b8d79aa1")
VersionAttribute(NTDDI_WIN8)
WebHostHiddenAttribute()

Members

The IValueConverter interface has these types of members:

Methods

Methods

The IValueConverter interface has these methods. It also inherits methods from the Object class.

Method	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.

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 to 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.

Note To data-bind to a custom value converter that is written in C++, the header file in which the IValueConverter implementation class is defined must be included, directly or indirectly, in one of the code-behind files. For more info, see Create your first Windows Store app using C++.

Examples

The following example shows how to implement the IValueConverter interface and use the converter when data binding to a collection of objects.

Important If you are coding in C++, remove the ConverterParameter attribute from the last TextBlock, because that particular string value is specific to .NET string formatting. Your entire element should look like this: <TextBlock Text="{Binding Path=ReleaseDate, Mode=OneWay, Converter={StaticResource FormatConverter}}" />.

XAML


<UserControl x:Class="ConverterParameterEx.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:local="using:ConverterParameterEx" 
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" >
        <Grid.Resources>
           <local:DateFormatter x:Key="FormatConverter" />
        </Grid.Resources>
        
        <ComboBox Height="60" Width="250" 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>

C++


using System;
using System.Collections.ObjectModel;
using System.Globalization;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.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, string language)
        {
            // Retrieve the format string and use it to format the value.
            string formatString = parameter as string;
            if (!string.IsNullOrEmpty(formatString))
            {
                return string.Format(
                    new CultureInfo(language), 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, string language)
        {
            throw new NotImplementedException();
        }
    }
}

Requirements

Minimum supported client	Windows 8
Minimum supported server	Windows Server 2012
Namespace	Windows.UI.Xaml.Data Windows::UI::Xaml::Data [C++]
Metadata	Windows.winmd

IValueConverter interface