WPF Template.FindName 返回始终为空
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/16839159/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
WPF Template.FindName return always null
提问by Enzojz
Template
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>
And the code in OnApplyTemplate
以及 OnApplyTemplate 中的代码
content = this.Template.FindName("PART_Canvas", this) as FrameworkElement;
the content returns always null, why it doesn't work?
内容总是返回null，为什么它不起作用？
if I replace with this, the program quits directly
如果我用这个替换，程序直接退出
content = this.ItemsPanel.FindName("PART_Canvas", this) as FrameworkElement;
回答by dkozl
With FindNameyou can find only elements declared in a Template. ItemsPanelis not part of that template. ItemsControlputs ItemsPanelinto ItemsPresenterplace holder via which you can access your Canvasbut first you need to name ItemsPresenterin your template:
有了FindName你可以找到只有在一个声明的元素Template。ItemsPanel不是该模板的一部分。ItemsControl放ItemsPanel成ItemsPresenter占位通过它您可以访问Canvas，但首先你需要的名字ItemsPresenter在你的模板：
<ControlTemplate TargetType="{x:Type local:Viewport}">
<Border>
<ItemsPresenter x:Name="PART_ItemsPresenter"/>
</Border>
</ControlTemplate>
then, using VisualTreeHelperget your Canvas, but I think earliest place when you can call code below is when FrameWorkElementis Loaded. This is my example:
然后，使用VisualTreeHelperget your Canvas，但我认为您可以在下面调用代码的最早位置是 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);
}
}
