Why is event not firing in WPF/MVVM application?

Question

I have the following NavBar, with the Content data template marked up as follows:

<dxn:NavBarControl Name="SideMenuNavBar" DataContext="{Binding}" IsEnabled="{Binding Enabled}" ItemsSource="{Binding Bars}" HorizontalAlignment="Left" VerticalAlignment="Stretch" Margin="1"> <dxn:NavBarControl.Resources> <Style TargetType="dxn:NavBarGroup"> <Setter Property="Header" Value="{Binding DisplayText}"/> <Setter Property="Content" Value="{Binding MenuItems}"/> <Setter Property="DisplaySource" Value="Content"/> <Setter Property="ContentTemplate"> <Setter.Value> <DataTemplate> <TreeView ItemsSource="{Binding}"> <TreeView.ItemTemplate> <HierarchicalDataTemplate ItemsSource="{Binding Path=ChildItems}" DataType="{x:Type common:MenuItemBase}"> <TextBlock Text="{Binding ItemText}" HorizontalAlignment="Stretch"> <TextBlock.ContextMenu> <ContextMenu DataContext="{Binding RelativeSource={RelativeSource Mode=Self}}"> <MenuItem Header="{Binding MenuText}" Click="MenuItem_OnClick" /> </ContextMenu> </TextBlock.ContextMenu> </TextBlock> </HierarchicalDataTemplate> </TreeView.ItemTemplate> </TreeView> </DataTemplate> </Setter.Value> </Setter> </Style> </dxn:NavBarControl.Resources> <dxn:NavBarControl.View> <dxn:NavigationPaneView GroupDisplayMode="Text" ItemDisplayMode="Text" MaxVisibleGroupCount="12"/> </dxn:NavBarControl.View> </dxn:NavBarControl>

The binding is working, as my one treeview of menu items appears correctly, yet when I click (MouseDown event) nothing happend, or when I double click, for the following handler, the handler does not execute:

private void Control_OnMouseDoubleClick(object sender, MouseButtonEventArgs e) { var x = sender; }

My breakpoint on var x = sender; never gets hit.

NOTE: I know I should not be using events but rather commands, or some other much less coupled code, but I urgently need to demo what happens when the user clicks a menu item, and before the event, my code for a command didn't fire either. What could be wrong here?

where do you register the MouseDown-Event? I only the the Click-Event of MenuItem — Jehof
– Jehof, Commented Apr 7, 2014 at 9:27

Community · Accepted Answer · 2017-05-23 12:11:12Z

First of all: ContextMenu is completly outside of your Controls VisualTree so normal Binding won't work at all unless you change your Binding as descibed here

Since you are using a code Behind Event try the following:

<MenuItem Header="{Binding MenuText}" MouseDown="MenuItem_MouseDown" />

And

private void MenuItem_MouseDown(object sender, MouseButtonEventArgs e) { var x = sender; }

Community · Accepted Answer · 2017-05-23 12:05:22Z

You should you Command Binding, ensuring you bind to the same context where the command is created.

If <MenuItem Header="{Binding MenuText}" ...> is binding correctly, than you should create a RelayCommand in the same context. and then bind to the click via

<MenuItem Click="{Binding ClickCommand}" ...?

But if you need a quickfix, you could use PreviewMouseButtonDown/Up in your NavBarControl and then check what was click in the handler?

See: get the name of the element on which I clicked / mousedown

<dxn:NavBarControl PreviewMouseUp="NavBar_PreviewMouseUp" ...>

And in the code behind.

private void NavBar_PreviewMouseUp(object sender, MouseButtonEventArgs e) { var mouseWasUpOn = e.Source as MenuItem; if (mouseWasUpOn != null) { string header = mouseWasDownOn.Header; } }

But do note, this is just a workaround if the normal event handlers are not working. Ideally you should be binding to a Command!

Yeah, I know, thanks, but the boss wanted to see if the menu click correctly opened a Delphi window in the proper area of the view. Once I got the Click event working, the other stuff was quite easy.
I have tried using a command as you say, but instead a DelegateCommand and I get an InvalidCastException: "Unable to cast object of type 'System.Reflection.RuntimeEventInfo' to type 'System.Reflection.MethodInfo'." I can't find a RelayCommand class.

ProfK · Accepted Answer · 2014-04-08 04:40:36Z

I'm quite new to WPF, and very new to the DevExpress WPF suite, so I just copied the original code above from an example somewhere. Then I thought to myself, why a ContextMenu? Then, I right clicked the menu item, and a blank context menu item appeared, and that fired the event. I removed the bloody context menu, and now my menu item is firing the event, like I wanted when I asked this question. The new structure of the TreeView is as follows:

<TreeView.ItemTemplate> <HierarchicalDataTemplate ItemsSource="{Binding Path=ChildItems}" DataType="{x:Type menus:MenuItemBase}"> <MenuItem DataContext="{Binding}" Header="{Binding ItemText}" Click="MenuItem_OnClick" /> </HierarchicalDataTemplate> </TreeView.ItemTemplate>

I'm still trying to get proper command binding working, but this answers my question about the events.

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