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DataTemplateSelector.SelectTemplate Method

When overridden in a derived class, returns a DataTemplate based on custom logic.

Namespace: System.Windows.Controls
Assembly: PresentationFramework (in presentationframework.dll)

public virtual DataTemplate SelectTemplate (
	Object item,
	DependencyObject container
)
public DataTemplate SelectTemplate (
	Object item, 
	DependencyObject container
)
public function SelectTemplate (
	item : Object, 
	container : DependencyObject
) : DataTemplate
You cannot use methods in XAML.

Parameters

item

The data object for which to select the template.

container

The data-bound object.

Return Value

Returns a DataTemplate or a null reference (Nothing in Visual Basic). The default value is a null reference (Nothing in Visual Basic).

Typically, you use a template selector when you have more than one data template defined for the same type of objects. For example, if your binding source is list a list of student objects and you want to apply a particular template to the part-time students. You can do this by creating a class that inherits from DataTemplateSelector and overriding the SelectTemplate method. Once your class is defined you can assign an instance of the class to the template selector property of your element.

In this example, the binding source is a list of Task objects. One of the properties of a Task object is Priority. There are two data templates defined, myTaskTemplate and importantTaskTemplate.

To supply logic to choose which DataTemplate to use based on the Priority value of the data object, create a subclass of DataTemplateSelector and override the SelectTemplate method. In the following example, the SelectTemplate method provides logic to return the appropriate template based on the value of the Priority property. The template to return is found in the resources of the enveloping Window element.

using System.Windows;
using System.Windows.Controls;

namespace SDKSample
{
    public class TaskListDataTemplateSelector : DataTemplateSelector
    {
        public override DataTemplate
            SelectTemplate(object item, DependencyObject container)
        {
            if (item != null && item is Task)
            {
                Task taskitem = item as Task;
                Window window = Application.Current.MainWindow;

                if (taskitem.Priority == 1)
                    return
                        window.FindResource("importantTaskTemplate") as DataTemplate;
                else
                    return
                        window.FindResource("myTaskTemplate") as DataTemplate;
            }

            return null;
        }
    }
}

We can then declare the TaskListDataTemplateSelector as a resource:

  <Window.Resources>

	...

    <local:TaskListDataTemplateSelector x:Key="myDataTemplateSelector"/>

	...

</Window.Resources>

To use the template selector resource, assign it to the ItemTemplateSelector property of the ListBox. The ListBox calls the SelectTemplate method of the TaskListDataTemplateSelector for each of the items in the underlying collection. The call passes the data object as the item parameter. The DataTemplate that is returned by the method is then applied to that data object.

<ListBox Width="400" Margin="10"
         ItemsSource="{Binding Source={StaticResource myTodoList}}"
         ItemTemplateSelector="{StaticResource myDataTemplateSelector}"
         HorizontalContentAlignment="Stretch"/>

For the complete sample, see Introduction to Data Templating Sample.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0

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