呈现模式视图控制器时的异常：NSInternalInconsistencyException

Question

when I try to present a modal view controller, an exception occurs:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', 
reason: 'Attempting to begin a modal transition from <UINavigationController: 0x1d906060>
to <UINavigationController: 0x1da7a6d0> while a transition is already in progress. Wait
for viewDidAppear/viewDidDisappear to know the current transition has completed'

Now, I read similar questions, where they simply opened the modal view with a tiny delay, like

[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(openModalController) userInfo:nil repeats:NO];

The presentation looks like this:

- (void)openImage:(ImageModel *)imageModel{
FullscreenImageViewController_iPhone * controller = [[FullscreenImageViewController_iPhone alloc] init];
controller.imageModel = imageModel;
UINavigationController * navController = [[UINavigationController alloc] initWithRootViewController:controller];
UIViewController * visibleController = [[AppDelegate_iPhone app] visibleViewController];
[visibleController presentViewController:navController animated:YES completion:^{

}];
}

This can´t be the real solution, can it? How can I check, if some transition is going on somewhere in my app and the open the new modal view right after the current transition has finished?

Answer 1

This works for me. If you use the isBeingPresented and isBeingDismissed methods of UIViewController to test whether a presentation or dismissal is ongoing, wait a while and try again:

- (void) presentVC {    
    if (presentingVC.isBeingPresented || presentingVC.isBeingDismissed) {
         double delayInSeconds = 0.3;
         dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
         dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
               [self presentVC];
         });
    }
    else {
        [presentingVC presentViewController:presentedVC animated:NO completion:nil];
    }
}