相关疑难解决方法(0)

UPDATE

从C#6开始,这个问题的答案是:

SomeEvent?.Invoke(this, e);

我经常听到/阅读以下建议:

在检查事件之前,请务必复制事件null并将其触发.这将消除线程的潜在问题,其中事件变为null位于您检查null和触发事件的位置之间的位置:

// Copy the event delegate before checking/calling
EventHandler copy = TheEvent;

if (copy != null)
    copy(this, EventArgs.Empty); // Call any handlers on the copied list

更新:我从阅读中了解到这可能还需要事件成员的优化,但Jon Skeet在他的回答中指出CLR不会优化副本.

但同时,为了解决这个问题,另一个线程必须做到这样的事情:

// Better delist from event - don't want our handler called from now on:
otherObject.TheEvent -= OnTheEvent;
// Good, now we can be certain that OnTheEvent will not run...

实际的顺序可能是这种混合物:

// Copy the event delegate before checking/calling
EventHandler copy …

这段代码为名为的事件添加了新的EventHandler寄存器NewMail(eventargs类被命名NewMailEventArgs.

// A PUBLIC add_xxx method (xxx is the event name)
// Allows methods to register interest in the event.
public void add_NewMail(EventHandler<NewMailEventArgs> value) {
  // The loop and the call to CompareExchange is all just a fancy way
  // of adding a delegate to the event in a thread-safe way.
  EventHandler<NewMailEventArgs> prevHandler;
  EventHandler<NewMailEventArgs> newMail = this.NewMail;
  do {
     prevHandler = newMail;
     EventHandler<NewMailEventArgs> newHandler = (EventHandler<NewMailEventArgs>)Delegate.Combine(prevHandler, value);
     newMail = Interlocked.CompareExchange<EventHandler<NewMailEventArgs>>(ref this.NewMail, newHandler, prevHandler);
    }
  while(newMail != …