注销事件与委托的新实例 [英] Unregister events with new instance of the delegate

问题描述

EventHandler a = new EventHandler(control_RegionChanged);
EventHandler b = new EventHandler(control_RegionChanged);

 if (a == b)
 {
     Console.WriteLine("Same!");
 }
 else
 {
     Console.WriteLine(a.GetHashCode() + " " + b.GetHashCode());
 }

这写一样！控制台

control.RegionChanged += new EventHandler(control_RegionChanged);
control.RegionChanged -= new EventHandler(control_RegionChanged);

这代码执行后，在事件处理程序 ？未登记

After this code executes, is the EventHandler unregistered?

推荐答案

是的;代表们在实例比较，的MethodInfo ;如果这些是相同的，那么它会工作。试图取消匿名方法时，问题就来了; 。在这种情况下，你必须坚持到委托的引用，以取消

Yes; delegates are compared on the instance and MethodInfo; if those are the same, then it will work. The problem comes when trying to unsubscribe an anonymous method; in that case, you must keep a reference to the delegate in order to unsubscribe.

所以：

这是罚款：

control.SomeEvent += obj.SomeMethod;
//...
control.SomeEvent -= obj.SomeMethod;

但是，这是非常高风险的：

But this is much riskier:

control.SomeEvent += delegate {Trace.WriteLine("Foo");};
//...
control.SomeEvent -= delegate {Trace.WriteLine("Foo");};

匿名方法的正确方法是：

The correct process with anonymous methods is:

EventHandler handler = delegate {Trace.WriteLine("Foo");};
control.SomeEvent += handler;
//...
control.SomeEvent -= handler;

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