NSURLConnection仍然调用委托AFTER cancel方法已被调用

Question

Having a problem with NSURLConnection, if I create a NSURLConnection and call [connection connectionWithRequest] let it load a little then call [connection cancel] most of the time that works fine. However occasionally even after I call [connection cancel] the connection's delegate still gets called (which crashes the app). Googling around it looks like the problem here is a race condition in the runloop, I cancel the connection and release the delegate but before the runloop cycles it calls the delegate functions -> crash.

Is there a way for me to, after I call [connection cancel] confirm the connection has actually canceled? Even a crappy while() loop will do :(

Answer 1

You should not release the connection & associated storage until your delegate receives either a connectionDidFinishLoading: or a connectionDidFailWithError: message.

Delegates are not normally retained by the object they're acting as delegate for . However in this case it is, so the delegate should not become invalid while the NSURLConnection is still referring to it, unless you're over-releasing it somehow.

Answer 2

I have not yet run into this problem, but this could also work without tying up your delegate object:

Since all delegate methods receive the calling Connection object as a parameter and you also know your actual active Connection object (or nil), simply ignore the delegation actions by comparing the two objects. This way a cancelled "ghost" Connection object can still call the delegate but not interfere with its internals.

- (void) connection:(NSURLConnection*) connection didReceiveData:(NSData*) data
{
    if(connection != _URLConnection){return;}
    ...
    [_incomingData appendData:data];
    ...
}

where _URLConnection is a property in your delegate set to an active Connection, or nil.