RelativeSource and Popup

Question

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";
}

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

System.Exception: BindingExpression_CannotFindAncestor.

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

Why does the relative source binding not work?

score 10 · Accepted Answer · answered Feb 18 '13 at 16:41

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; 
    }

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

Ok. That's clear for popup control. Is there a way of using Relative source in ComboBoxItemTemplate? — Alexander Boriskin, Feb 18 '13 at 17:22

score 2 · Answer 2 · answered Jun 27 '13 at 13:45

2

You can make small hack: setup DataContext via resources.

<Grid.Resources>
    <Style TargetType="TextBlock">
        <Setter Property="DataContext" Value="{Binding ElementName=myGrid, Path=DataContext}" />
    </Style>
</Grid.Resources>

answered Jun 27 '13 at 13:45

Rover

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score 2 · Answer 3 · answered Jun 27 '13 at 14:42

As others have mentioned, it's because the Popup is not part of the visual tree. Instead, you can use the Popup's PlacementTarget property to get back to the visual tree:

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

for situations where you have no control of the placement target see the Hack by Rover — user487779, Nov 25 '20 at 10:10

score 0 · Answer 4 · answered Feb 18 '13 at 16:37

Popups are not part of the visual tree.

Relative Source "Gets or sets the binding source by specifying its location relative to the position of the binding target (MSDN)". Since Popups are not part of the visual tree of the control that is showing it, it will not be able to resolve anything outside of the popup.

RelativeSource and Popup

4 Answers4

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