WPF CanExecuteChanged

繼承ICommand ,RelayCommand命令

public class RelayCommand : ICommand
    {
        private readonly Action _execute;
        private readonly Func<bool> _canExecute;
        public event EventHandler CanExecuteChanged;
        public RelayCommand(Action execute) : this(execute, null)
        {
        }
        public RelayCommand(Action execute, Func<bool> canExecute)
        {
            if (execute == null)
            {
                throw new ArgumentNullException("execute");
            }
            this._execute = execute;
            this._canExecute = canExecute;
        }
        public void RaiseCanExecuteChanged()
        {
            EventHandler canExecuteChanged = this.CanExecuteChanged;
            if (canExecuteChanged != null)
            {
                canExecuteChanged.Invoke(this, EventArgs.Empty);
            }
        }
        [DebuggerStepThrough]
        public bool CanExecute(object parameter)
        {
            return this._canExecute == null || this._canExecute.Invoke();
        }
        public void Execute(object parameter)
        {
            this._execute.Invoke();
        }
    }

我們改變SaveCommand的CanExecute從false到true，而save命令執行的狀態。CanExecuteChanged事件和客戶端調用CanExecute方法，.在實踐中，這將使一個“保存”按鈕，該按鈕被綁定到SaveCommand改變它的狀態從禁用和重新啟用。

public class BlingViewModel
        {
            private DelegateCommand<object> _saveCommand;
            private bool _canSaveExecute = true;
            public ICommand SaveCommand
            {
                get
                {
                    if (_saveCommand == null)
                    {
                        _saveCommand = new DelegateCommand<object>(executeMethod: _ => Save(), canExecuteMethod: _ => _canSaveExecute);
                    }
                    return _saveCommand;
                }
            }
            private void Save()
            {
                _canSaveExecute = false;
                _saveCommand.RaiseCanExecuteChanged();
                Console.WriteLine("Saving...");
                _canSaveExecute = true;
                _saveCommand.RaiseCanExecuteChanged();
            }
        } 

.也可以直接調用System.Windows.Input.CommandManager.InvalidateRequerySuggested()讓你的CanExecute處理程序重新評估。