Exit MenuItem Is Forever Disabled - wpf

Question

I have a Exit menu item in a WPF application. When I moved the project over to utilize Caliburn Micro it has become disabled when launching the application.
<MenuItem Header="E_xit" InputGestureText="Alt+F4"
Command="ApplicationCommands.Close"/>
Even adding IsEnabled="True" does nothing. If I remove the command Command="ApplicationCommands.Close", the menu item is enabled on startup (but obviously I want the Close command to remain attached).
My guess is there must be some kind of method or property I'm not aware of, or maybe I am not initializing the main window properly? Here is my AppBootstrapper:
public class AppBootstrapper : BootstrapperBase
{
SimpleContainer container;
public AppBootstrapper()
{
Start();
}
protected override void Configure()
{
container = new SimpleContainer();
container.Singleton<IWindowManager, WindowManager>();
container.Singleton<IEventAggregator, EventAggregator>();
container.PerRequest<IShell, MainWindowViewModel>();
var currentParser = Parser.CreateTrigger;
Parser.CreateTrigger = (target, triggerText) => ShortcutParser.CanParse(triggerText)
? ShortcutParser.CreateTrigger(triggerText)
: currentParser(target, triggerText);
}
protected override object GetInstance(Type service, string key)
{
var instance = container.GetInstance(service, key);
if (instance != null)
return instance;
throw new InvalidOperationException("Could not locate any instances.");
}
protected override IEnumerable<object> GetAllInstances(Type service)
{
return container.GetAllInstances(service);
}
protected override void BuildUp(object instance)
{
container.BuildUp(instance);
}
protected override void OnStartup(object sender, System.Windows.StartupEventArgs e)
{
DisplayRootViewFor<IShell>();
}
protected override IEnumerable<Assembly> SelectAssemblies() {
return new[] {
Assembly.GetExecutingAssembly()
};
}
}

Answer 1

I suspect you haven't set CommandBinding for ApplicationCommands.Close.
In case CommandBinding could not be found, command will always return false from CanExecute method. So, to enable command you have to:
First, create CommandBinding at root element (may be at window) or at any parent element which needs to handle this command.
Second, provide CanExecute handler in that command binding and set e.CanExecute to True in that handler based on condition where you want to enable this menuItem.
Small sample to achieve what i said above:
<TextBox>
<TextBox.CommandBindings>
<CommandBinding Command="ApplicationCommands.Close"
Executed="CommandBinding_Executed"
CanExecute="CommandBinding_CanExecute"/>
</TextBox.CommandBindings>
<TextBox.ContextMenu>
<ContextMenu>
<MenuItem Header="E_xit" InputGestureText="Alt+F4"
Command="ApplicationCommands.Close"/>
</ContextMenu>
</TextBox.ContextMenu>
</TextBox>
and in code behind handlers:
private void CommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
{
}
private void CommandBinding_CanExecute(object sender,
CanExecuteRoutedEventArgs e)
{
e.CanExecute = true; <-- Set this to true to enable bindings.
}
You can read more about it here - How to enable a Command and Commanding Overview.