iPad模拟器出错，但iPhone出现错误

Question

I have a segue that I do like this:

[self performSegueWithIdentifier:@"PlanToBusiness" sender:self];

it works on the iPhone but not on the iPad. What I do is make a remote call to a server, and when the server response comes back correctly, I try to take the user to the new page with that segue.

It works on the iPhone simulator, but not the iPad (the identifying string is the same for both) and on the iPad it crashes with this error:

bool _WebTryThreadLock(bool), 0x68f9cb0: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now...
1   WebThreadLock
2   -[UITextRangeImpl isEmpty]
3   -[UITextRange(UITextSelectionAdditions) _isCaret]
4   -[UITextSelectionView setCaretBlinks:]
5   -[UIKeyboardImpl setCaretBlinks:]
6   -[UIKeyboardImpl setDelegate:force:]
7   -[UIKeyboardImpl setDelegate:]
8   -[UIPeripheralHost(UIKitInternal) _reloadInputViewsForResponder:]
9   -[UINavigationController navigationTransitionView:didStartTransition:]
10  -[UINavigationTransitionView transition:fromView:toView:]
11  -[UINavigationTransitionView transition:toView:]
12  -[UINavigationController _startTransition:fromViewController:toViewController:]
13  -[UINavigationController _startDeferredTransitionIfNeeded]
14  -[UINavigationController pushViewController:transition:forceImmediate:]
15  -[UINavigationController pushViewController:animated:]
16  -[UIStoryboardPushSegue perform]
17  -[UIStoryboardSegueTemplate perform:]
18  -[UIViewController performSegueWithIdentifier:sender:]
19  __41-[PlanBusinessController submitBusiness:]_block_invoke_0
20  __block_global_0
21  -[NSBlockOperation main]
22  -[__NSOperationInternal start]
23  -[NSOperation start]
24  __block_global_6
25  _dispatch_call_block_and_release
26  _dispatch_worker_thread2
27  _pthread_wqthread
28  start_wqthread

I am also not too used to reading Obective-C stack traces so I am having a hard time pinpointing what the problem is.

Here is how I do this:

- (IBAction)submitBusiness:(id)sender 
{    
     // Make a url to send

     NSURL *url = [NSURL URLWithString:full_encoded_url_string];
     NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];

        // ***************
        // TODO: ok I dont really understand what this is
        NSOperationQueue *queue = [[NSOperationQueue alloc] init];
        // **************

        [NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
         {   
                         // I took out a lot of the logic code that is not needed

                         [self performSegueWithIdentifier:@"PlanToBusiness" sender:self];
         }];
    }
}

Answer 1

When methods that touch the UI, such when performing a segue, it is important to make sure you are calling that code from the main thread. The easiest way to do that is to make a method like this:

- (void)performPlanToBusinessSegueOnMainThread
{
    [self performSegueWithIdentifier:@"PlanToBusiness" sender:self];
}

Then, you can call this method in your finished block like this:

[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
 {   
     // I took out a lot of the logic code that is not needed

     [self performSelectorOnMainThread:@selector(performPlanToBusinessSegueOnMainThread) 
                            withObject:nil 
                         waitUntilDone:YES];
 }];

It is a little circuitous, but it should fix your exception. It would be better if we could just call performSegueWithIdentifier in the performSelectorOnMainThread method, but it has too many arguments.