事件触发越来越多的时间 [英] Event fires more and more times

问题描述

我必须加载与加载到2 ContentControls，其中一个列表框显示项目和其他与编辑按钮2用户控件主视图中的Silverlight应用程序MVVM。当我点击编辑按钮，2个新的用户控件加载到ContentControls，一是表现数据进行编辑（EditData）等具有保存和取消按钮（EditAction）。
当我点击保存按钮，它提出了在单独GlobalEvents.cs像类中定义的事件：

I have a silverlight mvvm application that loads main view with 2 user controls loaded into 2 ContentControls, one with listbox showing items and other with edit button. When i click edit button, 2 new user controls load into the ContentControls, one showing data to edit (EditData) and other having Save and Cancel button (EditAction). When i click save button, it raises an event that is defined in seperate GlobalEvents.cs class like:

public event EventHandler OnSaveButtonClicked;  
public void RaiseSaveButtonClicked()  
{  
  this.OnSaveButtonClicked(this, EventArgs.Empty);  
}

和我订阅它在其他用户的控制EditData，因为我需要该转让通过编辑自定义EventArgs的数据，所以我已经把它的构造函数的视图模型：

and i subscribe to it in the other user control EditData, because i need to transfer that edited data via custom EventArgs, so i have put in the constructor of it's ViewModel:

this.globalEvents.OnSaveButtonClicked += (s, e) => SaveData();  

和在保存数据：

public void SaveData()  
{  
    globalEvents.RaiseSaveData(EditedGuy);     
}  

这引起了加载以前的用户控件到他们ControlContent和节目编辑的数据的另一个事件在列表框中。这就是所有罚款，但每当我点击编辑，然后再保存，它引发事件两次，再3次，然后4等。我怎样才能使它得到提升只有一次？我想这可能是因为每次我点击编辑，用户控件的新实例被加载，我不知道，也许是订阅的事件撑地，所以我试图粘贴

which raises another event that loads previous user controls into their ControlContent and shows edited data in list box. Thats all fine, but whenever i click on edit and then save again, it raises the event twice, and again 3 times, then 4 and so on. How can i make it to be raised only ONE time? I thought it could be because every time i click edit, a new instance of the user control is loaded and i dont know, maybe the subscription to the event stays, so i have tried to paste

this.globalEvents.OnSaveButtonClicked -= (s, e) => SaveData(); 

的Dispose（）方法，但没有成功。我怎样才能使这项工作？

to the Dispose() method but without success. How can i make this work?

推荐答案

当你想从事件注销不能使用lambda表达式。

You can't use lambdas when you want to unregister from events.

this.globalEvents.OnSaveButtonClicked += (s, e) => SaveData(); 

这将创建一个实例 - 我们称之为例如A - EventHandler类型，并将其添加为处理程序

This will create one instance - let's call it instance A - of type EventHandler and add it as a handler.

this.globalEvents.OnSaveButtonClicked -= (s, e) => SaveData(); 

这不会从活动中删除实例的，但创建一个新的实例 - 实例B - ，并尝试从事件中删除

This will not remove instance A from the event but create a new instance - instance B - and tries to remove it from the event.

要解决这个问题，可以创建一个小方法或保存匿名方法在一个领域：

To fix this problem, either create a little method or save that anonymous method in a field:

class ViewModel
{

    private EventHandler _saveButtonClickedHandler;
    // ...

    public ViewModel()
    {
        _saveButtonClickedHandler = (s, e) => SaveData();
        this.globalEvents.OnSaveButtonClicked += _saveButtonClickedHandler;
        // ...
    }

    public void Dispose()
    {
        this.globalEvents.OnSaveButtonClicked -= _saveButtonClickedHandler;
        // ...
    }

    // ...
}

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