检测PropertyChangedEventHandler何时发生变化

Question

当我观察变量时，我的PropertyChanged事件得到了正确设置，但在代码中的某处它被重置为null，我不知道如何确定发生了什么。

这里已经来到代码：

public event PropertyChangedEventHandler PropertyChanged; 

    //this is in the NotifyTaskCompletion class, as used from the blog 
// http://msdn.microsoft.com/en-us/magazine/dn605875.aspx 
    private async Task WatchTaskAsync(Task task) 
    { 
     try 
     { 
      await task; //After this task, PropertyChanged gets set to a non-null method("Void OnPropertyChanged()") 
     } 
     catch 
     { 
     } 
     //PropertyChanged, which was set to a value after the task was run, and still not null during IdentifyCompleted getting set, is now null here 
     var propertyChanged = PropertyChanged; 
     if (propertyChanged == null) 
      return; 
     //other code 
} 


    //My Watch variable of PropertyChanged is still good after this setter is run. 
    public NotifyTaskCompletion<GraphicCollection> IdentifyCompleted 
    { 
     get { return _IdentifyCompleted; } 
     set 
     { 
      _IdentifyCompleted = value; 
     // _IdentifyCompleted.PropertyChanged+= new PropertyChangedEventHandler(this, new  PropertyChangedEventArgs("IdentifyCompleted")); 
      // NotifyPropertyChanged(); 
     } 
    } 

我的主要问题是，我不能使用{集;获取;}上的PropertyChanged试图找出它是越来越设置为null。所以我的主要问题是，除非任何人看到明显错误的东西，否则我将如何去查找它被设置为null的位置？感谢您的帮助。

编辑

按照过去的海报建议，我把我的代码如下：

private PropertyChangedEventHandler _propertyChanged; 
    public event PropertyChangedEventHandler PropertyChanged 
    { 
     add { _propertyChanged += value; } 
     remove { _propertyChanged -= value; } 
    } 

这里是问题。

//this is in my View Model. The ViewModel CONTAINS NotifyTaskCompletion<GraphicCollection> IdentifyCompleted which in turn implements INotifyPropertyChanged and has its own PropertyChanged that is not getting set 

    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "") 
    { 
     if (PropertyChanged != null) 
     { 
//This line sets the PopertyChanged in the view model AND in the NotifyTaskCompletion class somehow, but I don't know how it is setting it properly in the NotifyTaskCompletion class in my other project where this code works, When I step through this line in my code, it doesn't trigger 
//the add{} of the PropertyChanged in NotifyTaskCompletion, but it DOES in my other project... 
      PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); 
     } 
    } 

所以说这一切，我现在可以看到什么行应该工作，但我不知道为什么它不工作。任何其他想法？感谢你目前的帮助。

Answer 1

您可以编写自己的事件访问：

private PropertyChangedEventHandler propertyChanged; 
public event PropertyChangedEventHandler PropertyChanged { 
    add { propertyChanged += value; } 
    remove { propertyChanged -= value; } 
} 

然后，您可以设置断点。 请注意，这不是线程安全的。