谁能告诉我我提到的示例是否是回调机制的示例？

Question

class B
{
     public delegate void CallBack();
     public event CallBacl cllBack;

     void Publish()
     {
       cllBack();
     }
}

class A
{
     B b = new B();
     b.cllBack += new CallBack(test_this)

     public void test_this()
     {

     }
}

1. Does the above example represent a way of implementing the call back mechanism in .net?
2. Or else do I need to use BeginInvoke and endInvoke for the call back mechanism?

Answer 1

1. Yes, this is one method. Anyway I'll check this: if (cllBack != null) cllBack();
2. BeginInvoke (look here ) is used for asyncronous operations; the method you're using is the syncronous one.

Answer 2

There are many ways of implementing a callback mechanism, and using delegates is indeed one of them.

See this for info on begininvoke etc. also see that for an alternative.

Answer 3

one caveat that it cost me some pain:

b.cllBack += new CallBack(test_this)

of course adds a reference to b in a, so even if you do not use b anymore in any other place, b is still referenced and will not be garbage collected.

what i think is a neater approach:

class A
{
    private delegate B.CallBack myCallBack;
    private B b = new B();

    public A
    {
       myCallBack = new B.CallBack( test_this );
       b.cllBack += myCallBack;
    }


   public void Close()
   {
     c.cllBack -= myCallBack;
   }
}

In short you register when you need the callback, and unregister when you no longer need the callback.

hth

Mario

PS: be careful, your b is local to the ctor