.net Can'；t订阅DelegateCommand.CanExecuteChanged

我有两个ViewModels，其中一个包含另一个。内部有一个名为

PrintCommand

的

Microsoft.Practices.Prism.Commands.DelegateCommand

。最好订阅此命令的

CanExecuteChanged

事件。本部分照常实施：

OneViewModel.PrintCommand.CanExecuteChanged += CanExecuteChangedHandler;  

问题是此订阅不起作用。 反编译的

CanExecuteChanged

如下所示：

public event EventHandler CanExecuteChanged  
{  
  add  
  {  
    WeakEventHandlerManager.AddWeakReferenceHandler(ref this._canExecuteChangedHandlers, value, 2);  
  }  
  remove  
  {  
    WeakEventHandlerManager.RemoveWeakReferenceHandler(this._canExecuteChangedHandlers, value);  
  }  
}  

当我调试时，在订阅后的几个步骤后，

\u CanExecuteChangedHandler

似乎不包含任何活动的处理程序，即使订阅对象仍然存在。

---

我有点好奇，为什么会这样

答案在

CanExecuteChanged

的描述中找到。这是：

/// When subscribing to the <see cref="E:System.Windows.Input.ICommand.CanExecuteChanged"/> event using
///             code (not when binding using XAML) will need to keep a hard reference to the event handler. This is to prevent
///             garbage collection of the event handler because the command implements the Weak Event pattern so it does not have
///             a hard reference to this handler. An example implementation can be seen in the CompositeCommand and CommandBehaviorBase
///             classes. In most scenarios, there is no reason to sign up to the CanExecuteChanged event directly, but if you do, you
///             are responsible for maintaining the reference.

然后像这样使用它：

this.commandCanExecuteChangedHandler = new EventHandler(this.CommandCanExecuteChanged);
this.command.CanExecuteChanged += this.commandCanExecuteChangedHandler;

---

您的

CanExecuteChangedHandler如何？看起来怎么样？这是一个方法还是一个lambda表达式？
this.commandCanExecuteChangedHandler = new EventHandler(this.CommandCanExecuteChanged);
this.command.CanExecuteChanged += this.commandCanExecuteChangedHandler;