WPF CanExecuteChanged

继承ICommand ,RelayCommand命令

 1 public class RelayCommand : ICommand
 2     {
 3         private readonly Action _execute;
 4         private readonly Func<bool> _canExecute;
 5         public event EventHandler CanExecuteChanged;
 6         public RelayCommand(Action execute) : this(execute, null)
 7         {
 8         }
 9         public RelayCommand(Action execute, Func<bool> canExecute)
10         {
11             if (execute == null)
12             {
13                 throw new ArgumentNullException("execute");
14             }
15             this._execute = execute;
16             this._canExecute = canExecute;
17         }
18         public void RaiseCanExecuteChanged()
19         {
20             EventHandler canExecuteChanged = this.CanExecuteChanged;
21             if (canExecuteChanged != null)
22             {
23                 canExecuteChanged.Invoke(this, EventArgs.Empty);
24             }
25         }
26         [DebuggerStepThrough]
27         public bool CanExecute(object parameter)
28         {
29             return this._canExecute == null || this._canExecute.Invoke();
30         }
31         public void Execute(object parameter)
32         {
33             this._execute.Invoke();
34         }
35     }

View Code

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。

 1 public class BlingViewModel
 2         {
 3             private DelegateCommand<object> _saveCommand;
 4             private bool _canSaveExecute = true;
 5             public ICommand SaveCommand
 6             {
 7                 get
 8                 {
 9                     if (_saveCommand == null)
10                     {
11                         _saveCommand = new DelegateCommand<object>(executeMethod: _ => Save(), canExecuteMethod: _ => _canSaveExecute);
12                     }
13                     return _saveCommand;
14                 }
15             }
16             private void Save()
17             {
18                 _canSaveExecute = false;
19                 _saveCommand.RaiseCanExecuteChanged();
20                 Console.WriteLine("Saving...");
21                 _canSaveExecute = true;
22                 _saveCommand.RaiseCanExecuteChanged();
23             }
24         }

View Code

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