Wpf how to bind to commands in the ancestor's viewmodel

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My English is bad, so I don't know if I can make it clear, sorry about that.
And I really don't know how to explain it when trying to do some research.

Currently, I have a page which is a UserConstrol called "ToolPathPage", and it contains another UserControl called "ToolPathDataControl" which contains nothing but a DataGrid.

Now I want to bind a Command in the ToolPathPageViewModel to a MenuItem in ToolPathDataControl.xaml.

What I have tried:

XML

<DataGrid.ContextMenu>
    <ContextMenu >
        <MenuItem Header="Clear" Command="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type local:ToolPathPage},AncestorLevel= 1}, Path=DataContext.(viewModel:ToolPathPageViewModel.Clear_AllCommand)}"/>
    </ContextMenu>
</DataGrid.ContextMenu>

In the Output window it says:

Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='mTracker.ToolPathPage', AncestorLevel='1''. BindingExpression:Path=DataContext.(0); DataItem=null; target element is 'MenuItem' (Name=''); target property is 'Command' (type 'ICommand')

Posted 30-Oct-18 21:32pm

0x222fe

Updated 2-Nov-18 17:07pm

v3

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Comments

Graeme_Grant 31-Oct-18 21:45pm

"BindingExpression:Path=DataContext.(0); DataItem=null;" - can't find the DataContext that you are looking for...

0x222fe 31-Oct-18 21:58pm

Thanks for the reply, but I did set the DataContext of the ToolPathPage to ToolPathPageViewModel.
And does this means the ToolPathPage is successfully found as an ancestor?

Graeme_Grant 31-Oct-18 22:08pm

You can use the XAML inspector in VS2017 to check ;)

Richard Deeming 2-Nov-18 10:23am

The context menu is not part of the visual tree, so a "find ancestor" binding won't work.

You might be able to find a workaround based on this article:
WPF: ContextMenu Strikes Again. DataContext Not Updated[^]

0x222fe 2-Nov-18 22:58pm

It works, thanks a lot!

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0x222fe · Accepted Answer · 2018-11-02T17:08:00

Thanks to @RichardDeeming, I got my final solution:

XML

<DataGrid Tag="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type local:ToolPathPage}},Path=DataContext.(viewModel:ToolPathPageViewModel.Clear_AllCommand)}">
    <DataGrid.ContextMenu>
        <ContextMenu>
            <MenuItem Header="Clear" Command="{Binding PlacementTarget.Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=ContextMenu}}"/>
        </ContextMenu>
    </DataGrid.ContextMenu>
</DataGrid>