Why does delegate use weak references?

For example, set the delegate of B to A on the page, //. in m, B * B = [B alloc] init]; B. delegate = self; [self. view addSubview: B]; [B release]; then 1. A is responsible for creating B, and A's lifecycle must be longer than B (B exists, A must also exist; A exists, B may not exist) that is to say in B (instance B) when A (Instance) exists, so there is no need to use retain to count the reference + 1, assign is enough to 2. let's take A look at the following situation: If A crashes before B (the instance of a is first destroyed by release), then of course the method in a is not called by B after [A relase, however, when using retain, A is still not destroyed, so the method in A will still be called by B, but assgin does not have this problem 3. in essence, delegate is a pointer (assuming: ccPoint) pointing to a class that exists before it. We use del The egate Pointer Points to the existing pointer (ccPoint). Then, through delegate, that is, ccPoint, you can access the instance method in CCClass 4. avoid retain cycle, that is, there are two objects A and B, there is an instance variable of B in A, and there is another instance variable of A in B. to release A, you must releaseA B, to release B, there must be A in release B. In this way, A Retain Circle is generated, and a B cannot be dealloc. the Method to Solve Retain Circle is to use weak reference. The weak reference does not have the ownership of the referenced Object, so it does not need to be release, thus solving the Retain Circle problem. to prevent the occurrence of Retain Circle, delegate is usually weakly referenced. Therefore, we generally do not need to regrade a delegate. NSURLConnection is an exception.