Question

I ran into the situation where my class is making one asynchronous web call and the user requests another one (by moving a map) and can’t seem to properly cancel the NSURLConnection. I have seen some solutions to manage multiple async calls, but I do not want to do that because once the second request is made I no longer care about the first. I see that there is a cancel method, but I tried only calling it when the connection is nil, but the connection never seems to become nil despite a release on that object. Does anyone have a code sample of a proper cancel of an async NSURLConnect?

Answer 1

I don’t think you understand Objective C message passing or retain/release. Sending a retain or a release to an object will never cause the pointer you are holding for that object to become nil (though the object may no longer be valid). In other words:

id a = b;
[a release];

//since release never changes the value of a
assert(a == b);

Okay, so having said that, if somehow a release code change the value of object pointer you called it against to nil, then sending a another message to it would do nothing. Messages to nil are silently dropped. Remember, what you are holding is a pointer to the object, not the object itself.

Having said that, if you want to cancel an NSURLConnection. You have to send it the cancel before you release it (in general it is never correct to send message to objects after you have released them).

I really recommend you read Apple’s Memory Management documentation.