Convert method
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IValueConverter.Convert method

Modifies the source data before passing it to the target for display in the UI.


object Convert(
  object value, 
  Type targetType, 
  object parameter, 
  string language



Type: System.Object [.NET] | Platform::Object [C++]

The source data being passed to the target.


Type: System.Type [.NET] | TypeName [C++]

The type of the target property, as a type reference (System.Type for .NET, a TypeName helper struct for C++/CX).


Type: System.Object [.NET] | Platform::Object [C++]

An optional parameter to be used in the converter logic.


Type: System.String [.NET] | Platform::String [C++]

The language of the conversion.

Return value

Type: System.Object [.NET] | Platform::Object [C++]

The value to be passed to the target dependency property.


The targetType parameter of the Convert method uses different techniques of reporting the type system info, depending on whether you're programming with .NET or C++/CX.

  • For .NET, this parameter passes an instance of the System.Type type.
  • For C++/CX, this parameter passes a TypeName structure value. TypeName::Kind contains the simple string name of the type, similar to .NET's Type.Name.

When the converter is invoked by the binding engine, the targetType value is passed by looking up the property type of the target dependency property. You might use this value in your Convert implementation for one of two reasons:

  • Your converter has the expectation that it's always going to return objects of a specific type, and you want to verify that the binding that the converter is called for is using the converter correctly. If not, you might return a fallback value, or throw an exception (but see "Exceptions from converters" below).
  • Your converter can return more than one type, and you want the usage to inform your converter which type it should return. For example, you could implement an object-to-object conversion and an object-to-string conversion within the same converter code.

language comes from the ConverterLanguage value of a specific binding, not system values, so you should expect that it might be an empty string.

parameter comes from the ConverterParameter value of a specific binding, and is null by default. If your converter uses parameters to modify what it returns, this usually requires some convention for validating what is passed by the binding and handled by the converter. A common convention is to pass strings that name modes for your converter that result in different return values. For example you might have "Simple" and "Verbose" modes that return different length strings that are each appropriate for display in different UI control types and layouts.

Exceptions from converters

The data binding engine does not catch exceptions that are thrown by a user-supplied converter. Any exception that is thrown by the Convert method, or any uncaught exceptions that are thrown by methods that the Convert method calls, are treated as run-time errors. If you are using the converter in situations where the binding can use fallbacks or otherwise show reasonable results even if a conversion failure occurs, consider having your converter return DependencyProperty.UnsetValue and not throw exceptions. DependencyProperty.UnsetValue is a sentinel value that has special meaning in the dependency property system, and bindings that are passed this value will use FallbackValue.

Another alternative to throwing exceptions is to return the original value unchanged, and let the binding instance handle what it might do with that value. In most cases UI bindings that fail won't be error cases. They just won't use the source value and will instead use DependencyProperty.UnsetValue to show nothing, or use fallbacks.

try/catch based on doing something to value is a common implementation pattern for the Convert method, but you shouldn't rethrow, for the reasons mentioned above.

For an example that shows how to implement the Convert method using the parameter and language parameters, see the IValueConverter interface.


The following example shows how to implement the Convert method using the parameter and language parameters.

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()

            // 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 (Windows 10 device family)

Device family

Universal, introduced version 10.0.10240.0

API contract

Windows.Foundation.UniversalApiContract, introduced version 1.0


Windows::UI::Xaml::Data [C++]



Requirements (Windows 8.x and Windows Phone 8.x)

Minimum supported client

Windows 8

Minimum supported server

Windows Server 2012

Minimum supported phone

Windows Phone 8.1 [Windows Runtime apps only]


Windows::UI::Xaml::Data [C++]



See also

XAML data binding sample
Data binding in depth



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