Menu click not firing its bound command

Question

I started out with this View:

<Window x:Class="MyApp.UI.Views.MainView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:MyApp.UI.Views"
        mc:Ignorable="d"
        Title="MyApp" Height="300" Width="500" WindowStartupLocation="CenterScreen">
  <Grid>
    <Button
      HorizontalAlignment="Left"
      VerticalAlignment="Top"
      Command="{Binding ShutdownCommand}"
      Content="_Exit" 
      Margin="390,225,0,0"
      Width="75"/>
  </Grid>
</Window>

Code-behind

Imports MyApp.UI.ViewModels

Namespace MyApp.UI.Views
  Public Class MainView
    Public Sub New(ViewModel As IMainViewModel)
      Me.InitializeComponent()

      Me.ViewModel = ViewModel
      Me.DataContext = Me.ViewModel
    End Sub

    Private Sub MainView_Loaded(Sender As MainView, e As RoutedEventArgs) Handles Me.Loaded
      Me.ViewModel.Load
    End Sub

    Private ReadOnly ViewModel As MainViewModel
  End Class
End Namespace

ViewModel

Imports MyApp.UI.Commands

Namespace MyApp.UI.ViewModels
  Public Class MainViewModel
    Implements IMainViewModel

    Public Sub New()
      Me.ShutdownCommand = New DelegateCommand(AddressOf Me.Shutdown)
    End Sub

    Public Sub Shutdown() Implements IMainViewModel.Shutdown
      Application.Current.Shutdown()
    End Sub

    Public Sub Load() Implements IMainViewModel.Load
    End Sub

    Public ReadOnly Property ShutdownCommand As ICommand
  End Class
End Namespace

DelegateCommand

Imports Intexx

Namespace MyApp.UI.Commands
  Public Class DelegateCommand
    Implements ICommand

    Public Sub New(Execute As Action(Of Object))
      Me.New(Execute, Nothing)
    End Sub

    Public Sub New(Execute As Action(Of Object), CanExecute As Func(Of Object, Boolean))
      If Execute.IsNothing Then
        Throw New ArgumentNullException(NameOf(Execute))
      Else
        Me._CanExecute = CanExecute
        Me._Execute = Execute
      End If
    End Sub

    Public Function CanExecute(Parameter As Object) As Boolean Implements ICommand.CanExecute
      Return Me._CanExecute.IsNothing OrElse Me._CanExecute(Parameter)
    End Function

    Public Sub Execute(Parameter As Object) Implements ICommand.Execute
      Me._Execute(Parameter)
    End Sub

    Public Sub RaiseCanExecuteChanged()
      RaiseEvent CanExecuteChanged(Me, EventArgs.Empty)
    End Sub

    Public Event CanExecuteChanged As EventHandler Implements ICommand.CanExecuteChanged

    Private ReadOnly _CanExecute As Func(Of Object, Boolean)
    Private ReadOnly _Execute As Action(Of Object)
  End Class
End Namespace

Clicking the Exit button works as expected. The application exits.

Then I added a menu:

<Window x:Class="MyApp.UI.Views.MainView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:MyApp.UI.Views"
        mc:Ignorable="d"
        Title="MyApp" Height="300" Width="500" WindowStartupLocation="CenterScreen">
  <Grid>
    <Menu>
      <MenuItem Header="_File">
        <MenuItem
          Header="E_xit"
          Command="{Binding ShutDownCommand}"/>
      </MenuItem>
      <MenuItem Header="_Help">
        <MenuItem Header="_About MyApp"/>
      </MenuItem>
    </Menu>
    <Button
      HorizontalAlignment="Left"
      VerticalAlignment="Top"
      Command="{Binding ShutdownCommand}"
      Content="_Exit" 
      Margin="390,225,0,0"
      Width="75"/>
  </Grid>
</Window>

Clicking the Exit button still works, but clicking File=>Exit produces no result. I didn't change anything in either my code-behind or my ViewModel.

This one is related, but not quite the same. My MenuItem with the bound command is the child, not the parent.

What am I missing here? Why doesn't a File=>Exit click call the bound command?

score 0 · Accepted Answer · answered Jul 10 '20 at 02:58

0

OK, got it.

Being a bit new to WPF, I'd forgotten that command bindings (among other things) are case sensitive.

When I change the MenuItem's command binding from ShutDownCommand to ShutdownCommand, it works. The application exits as expected.

It'd be nice if IntelliSense worked here.

answered Jul 10 '20 at 02:58

InteXX

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IntelliSense works when the DataContext is known: eg. DataContext set from Xaml or templates for known types. In your case you should look for binding errors in the output window when debugging. – Nawed Nabi Zada Jul 10 '20 at 08:51
`look for binding errors in the output window when debugging` I like that idea. Unfortunately, though, nothing appears in the output window—for me at least. None of the suggestions [here](https://stackoverflow.com/q/8850143) had any effect. – InteXX Jul 10 '20 at 16:20

Menu click not firing its bound command

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