NSURLConnection对象为零

Question

想知道为什么conndetailing = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];为零

//enter code here
NSMutableURLRequest * request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString:[NSString stringWithFormat:@"https://www.myscript.php"]]];
[request setHTTPMethod:@"POST"];
[request setValue:postLength forHTTPHeaderField:@"Content-Length"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setHTTPBody:postData];
[post release];

//conndetailing goes nil and due to which app crashes
conndetailing = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
[conndetailing scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
[conndetailing start];
[request release];
responseDatadetailing=[[NSMutableData data] retain];