Why is my WPF ContextMenu Item disabled? - wpf

Question

I have a small but annoying problem with my ContextMenu in a WPF application.
I use a DataTemplate for my List of ViewModel-objects to create the visual elements. In the DataTemplate I simply set my UserControl like this:
<!-- Define a data-template for the 'RoomViewModel' class. This generates the UI for each node. -->
<DataTemplate DataType="{x:Type model:RoomViewModel}">
<network:RoomView network:ConstraintView.ArgumentChanged="ConstraintView_ArgumentChanged"></network:RoomView>
</DataTemplate>
I want the RoomView to have a ContextMenu where a RelayCommand should be executed if the user clicks on the MenuItem. My UserControl for the RoomView looks like this at the moment:
<UserControl x:Name="userControl" x:Class="NetworkUI.RoomView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:network="clr-namespace:NetworkUI"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300" DataContextChanged="userControl_DataContextChanged">
<UserControl.Resources>
<!-- UI commands -->
<RoutedCommand x:Key="Commands.NewConstraintCmd"></RoutedCommand>
</UserControl.Resources>
<UserControl.CommandBindings>
<CommandBinding x:Name="newConst" Command="{StaticResource Commands.NewConstraintCmd}" Executed="NewConstraint_Executed"></CommandBinding>
</UserControl.CommandBindings>
<Grid Width="Auto" Height="Auto" MinWidth="50" >
<Grid.RowDefinitions>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="Auto"></RowDefinition>
</Grid.RowDefinitions>
<Grid Grid.Row="0" Width="Auto" Height="20" MinWidth="50" >
<Rectangle Stroke="Black" Fill="White" RadiusX="4" RadiusY="4" SnapsToDevicePixels="True" ></Rectangle>
<Grid Margin="-4" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" MinWidth="10" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<network:EditableTextBlock Grid.Column="1" Grid.Row="1" x:Name="nameTextBox" Text="{Binding Name, Mode=TwoWay}" HorizontalAlignment="Center" VerticalAlignment="Center" BorderBrush="{x:Null}" />
<network:ConnectorItem Grid.Row="1" Grid.Column="0" DataContext="{Binding Connectors[0]}" />
<network:ConnectorItem Grid.Row="1" Grid.Column="2" DataContext="{Binding Connectors[1]}" />
</Grid>
</Grid>
<StackPanel Grid.Row="1" x:Name="roomProperties" Width="Auto" HorizontalAlignment="Stretch" >
<ItemsControl ItemsSource="{Binding PropertyGroups}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<network:ConstraintCollectionView></network:ConstraintCollectionView>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</Grid>
<UserControl.ContextMenu>
<ContextMenu x:Name="contextMenu">
<MenuItem Header="new Constraint" Command="{StaticResource Commands.NewConstraintCmd}"></MenuItem>
</ContextMenu>
</UserControl.ContextMenu>
</UserControl>
I am not really sure if my UserControl code is ok. In my CodeBehind file I define a
public ICommand NewConstraintCmd;
-Command that should be executed when the user clicks the Item. My Executed handler is simple and looks like this:
private void NewConstraint_Executed(object sender, ExecutedRoutedEventArgs e) {
ViewModel.AddConstraint();
}
The ViewModel is indeed a RoomViewModel and the NewConstraintCmd is set in the DataContextChanged - event (not displayed here).
My simple question is, why is my ContextMenu-Item always disabled? I mean the RelayCommand.CanExecute is never checked, is this the problem maybe?
I didn't find any solution for my problem yet.
Thank you for any help!

Answer 1

Thank you Rohit Vats! I changed my ICommand definition to this:
public static readonly ICommand NewConstraint = new RelayCommand((rvm) => AddConstraint(rvm));
Since this is a static method I needed the parameter (the DataContext of my RoomView).
My Method is defined like this now:
private static void AddConstraint(object rvm) {
if (rvm is RoomViewModel)
(rvm as RoomViewModel).AddConstraint();
}
So first the parameter is checked and if it is ok (a RoomViewModel object) I call the actual function on the object.
I have no idea why it works now, really :/.
My XAML code for the MenuItem now looks like this:
<MenuItem Header="new Constraint" Command="network:RoomView.NewConstraint" CommandParameter="{Binding}"></MenuItem>
As mentioned before I need the CommandParameter to call a function on it. Since the needed Object is my DataContext I just use the {Binding} to pass the object.
This really works fine now, I hope it will work with InputBindings as well in the future :)!
Thank you again for the help!