WPF custom command in context menu are disabled until any button clicked

Ah ha! A question I can answer! Firstly, I should mention that I have personally found it easier to define and hook up commands in code rather than in XAML. It allows me to hook up the handlers for the commands a little more flexibly than an all XAML approach does.

You should work out what commands you want to have and what they relate to. In my application, I currently have a class for defining important application commands like so:

public static class CommandBank
{
  /// Command definition for Closing a window
  public static RoutedUICommand CloseWindow { get; private set; }

  /// Static private constructor, sets up all application wide commands.
  static CommandBank()
  {
    CloseWindow = new RoutedUICommand();
    CloseWindow.InputGestures.Add(new KeyGesture(Key.F4, ModifierKeys.Alt));
    // ...
  }

Now, because I wanted to keep the code all together, using a code only approach to Commands lets me put the following methods in the class above:

/// Closes the window provided as a parameter
public static void CloseWindowExecute(object sender, ExecutedRoutedEventArgs e)
{
  ((Window)e.Parameter).Close();
}

/// Allows a Command to execute if the CommandParameter is not a null value
public static void CanExecuteIfParameterIsNotNull(object sender, CanExecuteRoutedEventArgs e)
{
  e.CanExecute = e.Parameter != null;
  e.Handled = true;
}

The second method there can even be shared with other Commands without me having to repeat it all over the place.

Once you have defined the commands like this, you can add them to any piece of UI. In the following, once the Window has Loaded, I add command bindings to both the Window and MenuItem and then add an input binding to the Window using a loop to do this for all command bindings. The parameter that is passed is the Window its self so the code above knows what Window to try and close.

public partial class SimpleWindow : Window
{
  private void WindowLoaded(object sender, RoutedEventArgs e)
  {
    // ...
    this.CommandBindings.Add(
      new CommandBinding(
        CommandBank.CloseWindow,
        CommandBank.CloseWindowExecute,
        CommandBank.CanExecuteIfParameterIsNotNull));

    foreach (CommandBinding binding in this.CommandBindings)
    {
       RoutedCommand command = (RoutedCommand)binding.Command;
       if (command.InputGestures.Count > 0)
       {
         foreach (InputGesture gesture in command.InputGestures)
         {
           var iBind = new InputBinding(command, gesture);
           iBind.CommandParameter = this;
           this.InputBindings.Add(iBind);
         }
       }
    }

    // menuItemExit is defined in XAML
    menuItemExit.Command = CommandBank.CloseWindow;
    menuItemExit.CommandParameter = this;
    // ...
  }

  // ....
}

I then also later have event handlers for the WindowClosing and WindowClosed events, I do recommend you make the actual implementation of commands as small and generic as possible. As in this case, I didn't try to put code that tries to stop the Window closing if there is unsaved data, I kept that code firmly inside the WindowClosing event.

Let me know if you have any follow up questions. :)

I had the same issue. The command bindings stopped working once I moved them to the ViewModel from code behind. And in the viewmodel I had to change my ICommand from RoutedCommand to DelegateCommand. I was able to get it working in the following way -

Add Opened eventhandler to your context menu -

<ContextMenu x:Key="columnHeaderMenu" Opened="ContextMenu_Opened">
    <MenuItem Command="{Binding CutCommand}" Header="Test" />
    <MenuItem Header="Copy"/>
    <MenuItem Header="Paste"/>
</ContextMenu>

In the code behind, you would assign your ViewModel to the context menu's DataContext -

private void ContextMenu_Opened(object sender, RoutedEventArgs e)
{
    ContextMenu menu = sender as ContextMenu;
    menu.DataContext = _vm;
}