DataTemplateSelector.SelectTemplate(Object, DependencyObject) Method
Definition
Important
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When overridden in a derived class, returns a DataTemplate based on custom logic.
public:
virtual System::Windows::DataTemplate ^ SelectTemplate(System::Object ^ item, System::Windows::DependencyObject ^ container);public virtual System.Windows.DataTemplate SelectTemplate (object item, System.Windows.DependencyObject container);abstract member SelectTemplate : obj * System.Windows.DependencyObject -> System.Windows.DataTemplate
override this.SelectTemplate : obj * System.Windows.DependencyObject -> System.Windows.DataTemplatePublic Overridable Function SelectTemplate (item As Object, container As DependencyObject) As DataTemplateParameters
- item
- Object
The data object for which to select the template.
- container
- DependencyObject
The data-bound object.
Returns
Returns a DataTemplate or null. The default value is null.
Examples
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)
{
FrameworkElement element = container as FrameworkElement;
if (element != null && item != null && item is Task)
{
Task taskitem = item as Task;
if (taskitem.Priority == 1)
return
element.FindResource("importantTaskTemplate") as DataTemplate;
else
return
element.FindResource("myTaskTemplate") as DataTemplate;
}
return null;
}
}
}
Namespace SDKSample
Public Class TaskListDataTemplateSelector
Inherits DataTemplateSelector
Public Overrides Function SelectTemplate(ByVal item As Object, ByVal container As DependencyObject) As DataTemplate
Dim element As FrameworkElement
element = TryCast(container, FrameworkElement)
If element IsNot Nothing AndAlso item IsNot Nothing AndAlso TypeOf item Is Task Then
Dim taskitem As Task = TryCast(item, Task)
If taskitem.Priority = 1 Then
Return TryCast(element.FindResource("importantTaskTemplate"), DataTemplate)
Else
Return TryCast(element.FindResource("myTaskTemplate"), DataTemplate)
End If
End If
Return Nothing
End Function
End Class
End Namespace
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.
Remarks
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.
