CanExecute of ApplicationCommand does not update

Question

I would like to call an ApplicationCommand with a MenuItem-Click:

        <MenuItem Header="{StaticResource MenuItemSave}" Command="ApplicationCommands.Save"/>

In my ViewModel-Constructor I inizialize my bindings with:

    CommandBinding saveBinding = new CommandBinding(ApplicationCommands.Save, SaveCommand_Execute, SaveCommand_CanExecute);
    CommandManager.RegisterClassCommandBinding(typeof(ViewModel_Main), saveBinding);
    RegisterCommandBindings.Add(saveBinding);

Now I would like to handle the command, but it simply is not executeable. Even if it should be ALWAYS true.

private void SaveCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = true;
}
private void SaveCommand_Execute(object sender, ExecutedRoutedEventArgs e)
{
    //Stuff
}

I have also tried to update all bindings after my init function:

CommandManager.InvalidateRequerySuggested();

But my MenuItem stays disabled.

Thank you!

Answer 1

I would suggest using this implementation of ICommand

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;

namespace Common
{
    public class Command<TArgs> : ICommand
    {
        public Command(Action<TArgs> exDelegate)
        {
            _exDelegate = exDelegate;
        }

        public Command(Action<TArgs> exDelegate, Func<TArgs, bool> canDelegate)
        {
            _exDelegate = exDelegate;
            _canDelegate = canDelegate;
        }

        protected Action<TArgs> _exDelegate;
        protected Func<TArgs, bool> _canDelegate;

        #region ICommand Members

        public bool CanExecute(TArgs parameter)
        {
            if (_canDelegate == null)
                return true;

            return _canDelegate(parameter);
        }

        public void Execute(TArgs parameter)
        {
            if (_exDelegate != null)
            {
                _exDelegate(parameter);
            }
        }

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        bool ICommand.CanExecute(object parameter)
        {
            if (parameter != null)
            {
                var parameterType = parameter.GetType();
                if (parameterType.FullName.Equals("MS.Internal.NamedObject"))
                    return false;
            }

            return CanExecute((TArgs)parameter);
        }

        void ICommand.Execute(object parameter)
        {
            Execute((TArgs)parameter);
        }

        #endregion
    }
}