问题的事件处理程序从约什 - 史密斯的MVVM示例应用程序

问题描述

下面的代码是由约什 - 史密斯的MVVM示例：

The following code is from the MVVM sample by Josh Smith:

/// <summary>
/// Raised when this workspace should be removed from the UI.
/// </summary>
public event EventHandler RequestClose;

void OnRequestClose()
{
    //if (RequestClose != null)
    //        RequestClose(this, EventArgs.Empty);
    EventHandler handler = this.RequestClose;
    if (handler != null)
        handler(this, EventArgs.Empty);
 }

注释行是我的加法。我的问题是注释行会做同样的事情注释的行权？那么，为什么创建另一个事件处理程序的参考？还是我失去了一些东西在这里？谢谢

The commented lines are my addition. My question is the commented lines would do the same thing as the uncommented lines right? So why create another EventHandler reference? Or am I missing something here? Thanks

推荐答案

Tanmoy是正确的。这样做是为了防止被改变RequestClose的可能性（为空，例如）在其他线程后，您的如果，但你的RequestClose（）之前。

Tanmoy is right. This is done to prevent possibility of RequestClose being changed (to null, for example) in other thread after your "if" but before your "RequestClose()".

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