Sdílet prostřednictvím

Postupy: Vyhledání elementů DataTemplate-Generated

  • Článek

Tento příklad ukazuje, jak najít prvky, které jsou generovány DataTemplate.

Příklad

V tomto příkladu existuje ListBox, která je svázaná s některými daty XML:

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

ListBox používá následující DataTemplate:

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

Pokud chcete načíst prvek TextBlock generovaný DataTemplate určitého ListBoxItem, nejprve musíte získat ListBoxItem, najít ContentPresenter v rámci tohoto ListBoxItema následně zavolat FindName na DataTemplate, který je nastaven na této ContentPresenter. Následující příklad ukazuje, jak tyto kroky provést. Pro demonstrační účely tento příklad vytvoří dialogové okno, které zobrazuje textový obsah vygenerovaného textového bloku DataTemplate.

// 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)

Následuje implementace FindVisualChild, která používá VisualTreeHelper metody:

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

Viz také