WPF Relative source- Cannot find source for bindin

问题:

have you ever have a problem like this:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.UserControl', AncestorLevel='1''. BindingExpression:Path=DataContext; DataItem=null; target element is 'ContextMenu' (Name=''); target property is 'DataContext' (type 'Object')

Code:

<ContextMenu DataContext="{Binding Path=DataContext, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type UserControl}}}" 

Context Menu is in the:

ListBox-> ListBoxItemTemplate -> DataGrid -> DataGrid.ContextMenu

I have also another Binding in ListBox control, that works with no problems at all.

回答1:

The solution:

1) Set Tag property on ContextMenu owner to DataContext you wanted. 2) Set DataContext of ContextMenu to

DataContext="{Binding PlacementTarget, RelativeSource={RelativeSource Self}} 

3) Bind your elements like this:

Name_Of_Property="{Binding Tag.Name_Of_Property}"

回答2:

context menu is not part of the visual tree, so you use PlacementTarget within your binding

 <ContextMenu DataContext="{Binding Path=PlacementTarget.DataContext, RelativeSource=Self}" />

this would use the DataContext of the DataGrid