ApplicationCommand 的 CanExecute 不更新

Question

我想用 MenuItem-Click 调用 ApplicationCommand：

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

在我的 ViewModel-Constructor 中，我初始化我的绑定：

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

现在我想处理该命令，但它根本无法执行。即使它应该总是正确的。

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

我还尝试在我的 init 函数之后更新所有绑定：

CommandManager.InvalidateRequerySuggested();

但我的 MenuItem 仍然处于禁用状态。

谢谢！

Answer 1

我建议使用这个 ICommand 实现

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
    }
}