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Anleitung zum Finden von DataTemplate-Generated-Elementen

In diesem Beispiel wird gezeigt, wie man Elemente findet, die von einem DataTemplate generiert werden.

Beispiel

In diesem Beispiel gibt es eine ListBox , die an einige XML-Daten gebunden ist:

<ListBox Name="myListBox" ItemTemplate="{StaticResource myDataTemplate}"
         IsSynchronizedWithCurrentItem="True">
  <ListBox.ItemsSource>
    <Binding Source="{StaticResource InventoryData}" XPath="Books/Book"/>
  </ListBox.ItemsSource>
</ListBox>

ListBox verwendet die folgenden DataTemplate.

<DataTemplate x:Key="myDataTemplate">
  <TextBlock Name="textBlock" FontSize="14" Foreground="Blue">
    <TextBlock.Text>
      <Binding XPath="Title"/>
    </TextBlock.Text>
  </TextBlock>
</DataTemplate>

Wenn Sie das von einem bestimmten TextBlock generierte DataTemplate-Element abrufen möchten, müssen Sie das ListBoxItem abrufen, darin das ListBoxItem finden und dann das ContentPresenter-Element aufrufen, das für dieses ListBoxItem festgelegt ist. Das folgende Beispiel zeigt, wie Sie diese Schritte ausführen. Zu Demonstrationszwecken wird in diesem Beispiel ein Meldungsfeld erstellt, in dem der Textinhalt des DataTemplate-generierten Textblocks angezeigt wird.

// Getting the currently selected ListBoxItem
// Note that the ListBox must have
// IsSynchronizedWithCurrentItem set to True for this to work
ListBoxItem myListBoxItem =
    (ListBoxItem)(myListBox.ItemContainerGenerator.ContainerFromItem(myListBox.Items.CurrentItem));

// Getting the ContentPresenter of myListBoxItem
ContentPresenter myContentPresenter = FindVisualChild<ContentPresenter>(myListBoxItem);

// Finding textBlock from the DataTemplate that is set on that ContentPresenter
DataTemplate myDataTemplate = myContentPresenter.ContentTemplate;
TextBlock myTextBlock = (TextBlock)myDataTemplate.FindName("textBlock", myContentPresenter);

// Do something to the DataTemplate-generated TextBlock
MessageBox.Show("The text of the TextBlock of the selected list item: "
    + myTextBlock.Text);

' Getting the currently selected ListBoxItem
' Note that the ListBox must have
' IsSynchronizedWithCurrentItem set to True for this to work
Dim myListBoxItem As ListBoxItem = CType(myListBox.ItemContainerGenerator.ContainerFromItem(myListBox.Items.CurrentItem), ListBoxItem)

' Getting the ContentPresenter of myListBoxItem
Dim myContentPresenter As ContentPresenter = FindVisualChild(Of ContentPresenter)(myListBoxItem)

' Finding textBlock from the DataTemplate that is set on that ContentPresenter
Dim myDataTemplate As DataTemplate = myContentPresenter.ContentTemplate
Dim myTextBlock As TextBlock = CType(myDataTemplate.FindName("textBlock", myContentPresenter), TextBlock)

' Do something to the DataTemplate-generated TextBlock
MessageBox.Show("The text of the TextBlock of the selected list item: " & myTextBlock.Text)

Es folgt die Implementierung von FindVisualChild, die die VisualTreeHelper Methoden verwendet:

private childItem FindVisualChild<childItem>(DependencyObject obj)
    where childItem : DependencyObject
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);
        if (child != null && child is childItem)
        {
            return (childItem)child;
        }
        else
        {
            childItem childOfChild = FindVisualChild<childItem>(child);
            if (childOfChild != null)
                return childOfChild;
        }
    }
    return null;
}

Private Function FindVisualChild(Of childItem As DependencyObject)(ByVal obj As DependencyObject) As childItem
    For i As Integer = 0 To VisualTreeHelper.GetChildrenCount(obj) - 1
        Dim child As DependencyObject = VisualTreeHelper.GetChild(obj, i)
        If child IsNot Nothing AndAlso TypeOf child Is childItem Then
            Return CType(child, childItem)
        Else
            Dim childOfChild As childItem = FindVisualChild(Of childItem)(child)
            If childOfChild IsNot Nothing Then
                Return childOfChild
            End If
        End If
    Next i
    Return Nothing
End Function

Siehe auch