WPF CanExecuteChanged

继承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();
         }
     }

我们改变SaveCommand的CanExecute从false到true，而save命令执行的状态。CanExecuteChanged事件和客户端调用CanExecute方法，.在实践中，这将使一个“保存”按钮，该按钮被绑定到SaveCommand改变它的状态从禁用和重新启用。

 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();
             }
         } 

.也可以直接调用System.Windows.Input.CommandManager.InvalidateRequerySuggested()让你的CanExecute处理程序重新评估。