WPF: context menu in TreeViewItem binding to root

Question

I have TreeView control and I need to bind property from root (window/usercontrol) DataContext in context menu in that treeview.

 <TextBox Text="{Binding Header}"></TextBox> <TreeView ItemsSource="{Binding Items}" Grid.Row="1"> <TreeView.ItemContainerStyle> <Style TargetType="{x:Type TreeViewItem}"> <Setter Property="ContextMenu"> <Setter.Value> <ContextMenu> <MenuItem Header="{{ BINDING TO HEADER PROPERTY FROM WINDOW DATACONTEXT}}"/> </ContextMenu> </Setter.Value> </Setter> </Style> </TreeView.ItemContainerStyle> </TreeView> public ObservableCollection<string> Items { get; set; } public string Header { get { return _header; } set { _header = value; } }

I've tried multiple things: I've added x:Name="WindowRoot" to Window and {Binding Header, ElementName=WindowRoot} but it didn't work, I've tried multiple FindAncestor and RelativeSource but it didn't work.

Can someone help me?

Edit:

This is simplified case, in my normal application I use Unity + Prism, so ViewModel is AutoDiscovered (prism:ViewModelLocator.AutoWireViewModel="True") and it generally works. By "works" I mean: TreeView shows items from my collection, so it is connected, the problem is with context menu binding only.

In this simplified example I have ugly and simple code-behind, because I only want to test this ContextMenu binding:

public partial class MainWindow : Window { public ObservableCollection<string> Items { get; set; } private string _header = "testtest"; public string Header { get { return _header ; } set { _header = value; } } public MainWindow() { Items = new ObservableCollection<string>(); Items.Add("ItemTest"); InitializeComponent(); this.DataContext = this; } }

Try adding DataContext to your binding so DataContext.Header — Nicolas Pierre
– Nicolas Pierre, Commented Jun 3, 2017 at 22:35
@NicolasPierre Thanks for the idea, sadly it doesn't work too (it works finein TextBox which is directly in Window, so it is not problem with the property Header) — Andy
– Andy, Commented Jun 3, 2017 at 22:43
Should I do anything beside window.DataContext = MyViewModel? Binding in the <TextBox Text="{Binding Header}"></TextBox> above TreeView works fine. — Andy
– Andy, Commented Jun 3, 2017 at 22:47
Edit your question with how you bound the viewmodel if you would please — Nicolas Pierre
– Nicolas Pierre, Commented Jun 3, 2017 at 22:48

mm8 · Accepted Answer · 2017-06-05 17:36:26Z

You could bind the Tag property of the TreeViewItem to the parent window or user control using a {RelativeSource} and then bind the Header property of the MenuItem to the Tag property of the PlacementTarget of the ContextMenu:

<TreeView x:Name="tv" ItemsSource="{Binding Items}" Grid.Row="1"> <TreeView.ItemContainerStyle> <Style TargetType="{x:Type TreeViewItem}"> <Setter Property="Tag" Value="{Binding RelativeSource={RelativeSource AncestorType=Window}}" /> <Setter Property="ContextMenu"> <Setter.Value> <ContextMenu> <MenuItem Header="{Binding PlacementTarget.Tag.DataContext.Header, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/> </ContextMenu> </Setter.Value> </Setter> </Style> </TreeView.ItemContainerStyle> </TreeView>

The reason you cannot bind directly to any property of the window from the MenuItem is that a ContextMenu resides in a different element tree than the parent window or user control.

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