IMultiValueConverter.Convert Method

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. Handle anticipated problems by returning DependencyProperty.UnsetValue.

MultiBinding allows you to bind a binding target property to a list of source properties and then apply logic to produce a value with the given inputs. This example demonstrates how to use MultiBinding.

In the following example, NameListData refers to a collection of PersonName objects, which are objects that contain two properties, firstName and lastName. The following example produces a TextBlock that shows the first and last names of a person with the last name first.

<Window
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:c="clr-namespace:SDKSample"
  x:Class="SDKSample.Window1"
  Width="400"
  Height="280"
  Title="MultiBinding Sample">
	
  <Window.Resources>
    <c:NameList x:Key="NameListData"/>
    <c:NameConverter x:Key="myNameConverter"/>


...


</Window.Resources>


...


<TextBlock Name="textBox2" DataContext="{StaticResource NameListData}">
  <TextBlock.Text>
    <MultiBinding Converter="{StaticResource myNameConverter}"
                  ConverterParameter="FormatLastFirst">
      <Binding Path="FirstName"/>
      <Binding Path="LastName"/>
    </MultiBinding>
  </TextBlock.Text>
</TextBlock>


...


</Window>

To understand how the last-name-first format is produced, let's take a look at the implementation of the NameConverter:

public class NameConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        string name;

        switch ((string)parameter)
        {
            case "FormatLastFirst":
                name = values[1] + ", " + values[0];
                break;
            case "FormatNormal":
            default:
                name = values[0] + " " + values[1];
                break;
        }

        return name;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        string[] splitValues = ((string)value).Split(' ');
        return splitValues;
    }
}

NameConverter implements the IMultiValueConverter interface. NameConverter takes the values from the individual bindings and stores them in the values object array. The order in which the Binding elements appear under the MultiBinding element is the order in which those values are stored in the array. The value of the ConverterParameter attribute is referenced by the parameter argument of the Converter method, which performs a switch on the parameter to determine how to format the name.

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

Other Resources