相对来源和弹出窗口 [英] RelativeSource and Popup

问题描述

问题是 RelativeSource 在以下情况下不起作用.我用的是 Silverlight 5.

The problem is that RelativeSource does not work in the following case. I use silverlight 5.

//From MainPage.xaml
<Grid x:Name="LayoutRoot" Background="White" Height="100" Width="200">
    <Popup IsOpen="True">
        <TextBlock Text="{Binding Path=DataContext, RelativeSource={RelativeSource AncestorType=Grid}}" />
    </Popup>
</Grid>

//From MainPage.xaml.cs
public MainPage()
{
    InitializeComponent();
    DataContext = "ololo";
}

如果我在绑定上设置断点，我会得到错误:

If I set a breakpoint on the binding, I'll get Error:

系统异常:BindingExpression_CannotFindAncestor.

System.Exception: BindingExpression_CannotFindAncestor.

如果我使用 ElementName=LayoutRoot 而不是 RelativeSource，一切都会好的.

If I use ElementName=LayoutRoot instead of RelativeSource, everything will be OK.

为什么相对源绑定不起作用?

Why does the relative source binding not work?

推荐答案

Popup 就像 ContextMenu 、 ToolTip 控件，它们没有添加到 VisualTree 中.为此，您必须这样做

Popup is like ContextMenu , ToolTip controls , They are not added to the VisualTree. For this you will have to do like

<Grid x:Name="LayoutRoot" Height="100" Width="200" Background="Black">
    <Popup Grid.Row="0"  x:Name="popup" DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Mode=Self}}">
        <TextBlock Text="{Binding DataContext, ElementName=popup}" Background="Red" Width="30" Height="30" />
    </Popup>
</Grid>

public MainWindow()
    {
        InitializeComponent();
        DataContext = "abcd";
        popup.PlacementTarget = LayoutRoot; 
    }

我希望这会有所帮助.不像 ContextMenu 或 Tooltip 的情况，在这里您还必须指定 PlacementTarget.

I hope this will help.Not like in case of ContextMenu or Tooltip , here you will also have to specify the PlacementTarget.

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