How to: Convert Bound Data


This example shows how to apply conversion to data that is used in bindings.

To convert data during binding, you must create a class that implements the IValueConverter interface, which includes the Convert and ConvertBack methods.

The following example shows the implementation of a date converter that converts the date value passed in so that it only shows the year, the month, and the day. When implementing the IValueConverter interface, it is a good practice to decorate the implementation with a ValueConversionAttribute attribute to indicate to development tools the data types involved in the conversion, as in the following example:

    [ValueConversion(typeof(DateTime), typeof(String))]
    public class DateConverter : IValueConverter
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
            DateTime date = (DateTime)value;
            return date.ToShortDateString();

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
            string strValue = value as string;
            DateTime resultDateTime;
            if (DateTime.TryParse(strValue, out resultDateTime))
                return resultDateTime;
            return DependencyProperty.UnsetValue;

Once you have created a converter, you can add it as a resource in your Extensible Application Markup Language (XAML) file. In the following example, src maps to the namespace in which DateConverter is defined.

      <src:DateConverter x:Key="dateConverter"/>

Finally, you can use the converter in your binding using the following syntax. In the following example, the text content of the TextBlock is bound to StartDate, which is a property of an external data source.

              <TextBlock Grid.Row="2" Grid.Column="0" Margin="0,0,8,0"
                         Style="{StaticResource smallTitleStyle}">Start Date:</TextBlock>
              <TextBlock Name="StartDateDTKey" Grid.Row="2" Grid.Column="1" 
                  Text="{Binding Path=StartDate, Converter={StaticResource dateConverter}}" 
                  Style="{StaticResource textStyleTextBlock}"/>

The style resources referenced in the above example are defined in a resource section not shown in this topic.

Implement Binding Validation
Data Binding Overview
How-to Topics