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I have some problems in understanding RelativeSource binding behavior. Below is the code that binds Label content to StackPanel Tag correctly: 

<Window x:Class="Binding_RelativeSource.MainWindow" Tag="Window Tag"> <Grid Tag="Grid Tag"> <StackPanel Tag="StackPanel Tag" Height="100" HorizontalAlignment="Left" Margin="156,97,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200"> <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=1,AncestorType=StackPanel},FallbackValue=BindingFailed}" Height="28" Name="label1" /> </StackPanel> </Grid> </Window>

Above code does not bind Grid Tag, if I change AncestorType=Grid and AncestorLevel=2. I have 2 questions:

  1. I think I should change AncestorLevel to 2, to bind to Grid. But it worked for AncestorLevel=1. Why?

  2. I am also not able to bind label to Window tag.Please suggest.

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2 Answers 2

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The AncestorLevel is use to find the correct ancestor to bind to, this is because there could be more than one ancestor of that type.

Here is a scenario that shows this:

<Grid Tag="AncestorLevel 3"> <Grid Tag="AncestorLevel 2"> <Grid Tag="AncestorLevel 1"> <StackPanel Tag="StackPanel Tag" Height="100" HorizontalAlignment="Left" Margin="156,97,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200"> <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=1,AncestorType=Grid},FallbackValue=BindingFailed}" Height="28" /> <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=2,AncestorType=Grid},FallbackValue=BindingFailed}" Height="28" /> <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=3,AncestorType=Grid},FallbackValue=BindingFailed}" Height="28" /> </StackPanel> </Grid> </Grid> </Grid>

Result:

enter image description here

Alternative Method

But you can simplify the code by using ElementName binding, this uses the Name of the element

Example:

<Window x:Class="WpfApplication9.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="525" Name="MyWindow" Tag="This is the window"> <Grid Name="Grid1" Tag="First grid"> <Grid Name="Grid2" Tag="Second grid"> <Grid Name="Grid3" Tag="ThirdGrid"> <StackPanel Name="stackPanel1" Tag="StackPanel Tag" Height="160" HorizontalAlignment="Left" Margin="156,97,0,0" VerticalAlignment="Top" Width="200"> <Label Content="{Binding ElementName=MyWindow, Path=Tag}" Height="28" /> <Label Content="{Binding ElementName=Grid1, Path=Tag}" Height="28" /> <Label Content="{Binding ElementName=Grid2, Path=Tag}" Height="28" /> <Label Content="{Binding ElementName=Grid3, Path=Tag}" Height="28" /> <Label Content="{Binding ElementName=stackPanel1, Path=Tag}" Height="28" /> </StackPanel> </Grid> </Grid> </Grid> </Window>

Result:

enter image description here

If you want to bind back to the Window you can still use FindAncestor

<Window x:Class="WpfApplication9.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="525" Tag="This is the window"> <Grid> <StackPanel Height="100" HorizontalAlignment="Left" Margin="156,97,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200"> <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=Window},FallbackValue=BindingFailed}" Height="28" /> </StackPanel> </Grid>

Result:

enter image description here

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9 Comments

1. It means in my case if I do not mention AncestorLevel, it should be fine. I verified it, it's working for StackPanel & Grid without setting AncestorLevel property. But it's not working for Window, why? Can you give me the reason, please? 2. I understand, ElementName property binding. I have no problem with that. But, I want to know the reason, why RelativeSource binding is working for StackPanel and Grid, but not for Window. Please suggest.
It does work for window, Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=Window} works fine here
Oh, yes. It also worked for me. But it is binding at run time for window. For Grid & StackPanel it does at compile time. Any specific reason?
What VS version are you using?
I have done the same as your updated answer. But it updates binding at run time. I am using VS2010.
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Final conclusion from my end: It was VS2010 designer problem that it does not update RelativeSource binding for Window tag. It updates binding for other controls (I checked with Grid & StackPanel) in designer but for Winodw it gets updated at run time. Microsoft has done workaround in VS2012 for it.

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