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 class 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++


//
// MainPage.xaml.h
// Declaration of the MainPage class.
// 

#pragma once

#include "MainPage.g.h"

namespace IValueConverterExample
{

    // Simple business object.
    [Windows::UI::Xaml::Data::Bindable]
    public ref class Recording sealed 
    {
    public: 
        Recording (Platform::String^ artistName, Platform::String^ cdName, Windows::Foundation::DateTime release)
        {
            Artist = artistName;
            Name = cdName;
            ReleaseDate = release;
        }
        property Platform::String^ Artist;
        property Platform::String^ Name;
        property Windows::Foundation::DateTime ReleaseDate;
    };

    public ref class DateFormatter  sealed : Windows::UI::Xaml::Data::IValueConverter 
    {
        // This converts the DateTime object to the Platform::String^ to display.
    public:
        virtual Platform::Object^ Convert(Platform::Object^ value, Windows::UI::Xaml::Interop::TypeName targetType, 
            Platform::Object^ parameter, Platform::String^ language)
        {
            Windows::Foundation::DateTime dt = safe_cast<Windows::Foundation::DateTime>(value); 
            Windows::Globalization::DateTimeFormatting::DateTimeFormatter^ dtf =
                Windows::Globalization::DateTimeFormatting::DateTimeFormatter::ShortDate;
            return dtf->Format(dt); 
        }

        // No need to implement converting back on a one-way binding 
        virtual Platform::Object^ ConvertBack(Platform::Object^ value, Windows::UI::Xaml::Interop::TypeName targetType, 
            Platform::Object^ parameter, Platform::String^ language)
        {
            throw ref new Platform::NotImplementedException();
        }
    };

    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public ref class MainPage sealed
    {
    public:
        MainPage()
        {    
            m_myMusic = ref new Platform::Collections::Vector<Recording^>();

            // Add items to the collection.

            // You can use a Calendar object to create a Windows::Foundation::DateTime
            auto c = ref new Windows::Globalization::Calendar();
            c->Year = 2008;
            c->Month = 2;
            c->Day = 5;
            m_myMusic->Append(ref new Recording("Chris Sells", "Chris Sells Live",
                c->GetDateTime()));

            c->Year = 2007;
            c->Month = 4;
            c->Day = 3;
            m_myMusic->Append(ref new Recording("Luka Abrus",
                "The Road to Redmond", c->GetDateTime()));
            
            c->Year = 2007;
            c->Month = 2;
            c->Day = 3;
            m_myMusic->Append(ref new Recording("Jim Hance",
                "The Best of Jim Hance", dt));
            InitializeComponent();

            // Set the data context for the combo box.
            MusicCombo->DataContext = m_myMusic;    
        }


    protected:
        virtual void OnNavigatedTo(Windows::UI::Xaml::Navigation::NavigationEventArgs^ e) override;

    private:
        Windows::Foundation::Collections::IVector<Recording^>^ m_myMusic;
    };
}

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