c# - WPF Template.FindName 总是返回 null

Question

模板

<Style TargetType="{x:Type local:Viewport}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:Viewport}">
                <Border Background="{TemplateBinding Background}"
                        BorderBrush="{TemplateBinding BorderBrush}"
                        BorderThickness="{TemplateBinding BorderThickness}">
                    <ItemsPresenter/>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
    <Setter Property="ItemsPanel">
        <Setter.Value>
            <ItemsPanelTemplate>
                <Canvas x:Name="PART_Canvas" IsItemsHost="True"/>
            </ItemsPanelTemplate>
        </Setter.Value>
    </Setter>
</Style>

以及 OnApplyTemplate 中的代码

content = this.Template.FindName("PART_Canvas", this) as FrameworkElement;

内容总是返回null，为什么它不起作用？

如果我用这个替换，程序直接退出

content = this.ItemsPanel.FindName("PART_Canvas", this) as FrameworkElement;

Answer 1

FindName您只能找到在 a 中声明的元素Template。ItemsPanel不是该模板的一部分。ItemsControl放入占位符，您可以通过它访问您的ItemsPanel，但首先您需要在模板中命名：ItemsPresenterCanvasItemsPresenter

<ControlTemplate TargetType="{x:Type local:Viewport}">
   <Border>
      <ItemsPresenter x:Name="PART_ItemsPresenter"/>
   </Border>
</ControlTemplate>

然后，使用VisualTreeHelperget your Canvas，但我认为最早可以调用下面代码的地方是 when FrameWorkElementis Loaded。这是我的例子：

public class MyListBox : ListBox
{
  public MyListBox()
  {
      AddHandler(FrameworkElement.LoadedEvent, new RoutedEventHandler(ControlIsLoaded));
  }

  private void ControlIsLoaded(object sender, RoutedEventArgs e)
  {
      var canvas = VisualTreeHelper.GetChild(this.Template.FindName("PART_ItemsPresenter", this) as DependencyObject, 0);
  }
}