I have an UITabBarController, when initial run, I want to overlay a login view controller but received error.
Unbalanced calls to begin/end appearance transitions for < UITabBarController: 0x863ae00 >.
Below is the code.
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// Override point for customization after application launch.
self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
// Override point for customization after application launch.
UIViewController *lessonVC = [[[LessonViewController alloc] initWithNibName:@"LessonViewController" bundle:nil] autorelease];
UIViewController *programVC = [[[ProgramViewController alloc] initWithNibName:@"ProgramViewController" bundle:nil] autorelease];
UIViewController *flashcardVC = [[[FlashCardViewController alloc] initWithNibName:@"FlashCardViewController" bundle:nil] autorelease];
UIViewController *moreVC = [[[MoreViewController alloc] initWithNibName:@"MoreViewController" bundle:nil] autorelease];
UINavigationController *lessonNVC = [[[UINavigationController alloc] initWithRootViewController:lessonVC] autorelease];
UINavigationController *programNVC = [[[UINavigationController alloc] initWithRootViewController:programVC] autorelease];
UINavigationController *flashcardNVC = [[[UINavigationController alloc] initWithRootViewController:flashcardVC] autorelease];
UINavigationController *moreNVC = [[[UINavigationController alloc] initWithRootViewController:moreVC] autorelease];
self.tabBarController = [[[UITabBarController alloc] init/*WithNibName:nil bundle:nil*/] autorelease];
self.tabBarController.viewControllers = [NSArray arrayWithObjects:lessonNVC, programNVC, flashcardNVC, moreNVC, nil];
self.tabBarController.selectedIndex = 0;
self.window.rootViewController = self.tabBarController;
[self.window makeKeyAndVisible];
if (![[ZYHttpRequest sharedRequest] userID])
{
// should register or login firstly
LoginViewController *loginVC = [[LoginViewController alloc] initWithNibName:@"LoginViewController"
bundle:nil];
loginVC.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self.tabBarController presentModalViewController:loginVC animated:YES];
ZY_SAFE_RELEASE(loginVC);
}
return YES;
}
Anyone who can help me? Thanks in advance!
You need to wait to present the modal view controller until the next run loop. I ended up using a block (to make things more simple) to schedule the presentation for the next run loop:
Update:
As mentioned by Mark Amery below, just a simple dispatch_async
works, there's no need for a timer:
dispatch_async(dispatch_get_main_queue(), ^(void){
[self.container presentModalViewController:nc animated:YES];
});
/* Present next run loop. Prevents "unbalanced VC display" warnings. */
double delayInSeconds = 0.1;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[self.container presentModalViewController:nc animated:YES];
});
I suspect the problem is that you're trying to call presentModalViewController:
before the tab bar is done loading. Try moving the final logic onto the next event loop:
[self.window makeKeyAndVisible];
[self performSelector:(handleLogin) withObject:nil afterDelay:0];
}
- (void)handleLogin
{
if (![[ZYHttpRequest sharedRequest] userID])
{
// should register or login firstly
LoginViewController *loginVC = [[LoginViewController alloc] initWithNibName:@"LoginViewController"
bundle:nil];
loginVC.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self.tabBarController presentModalViewController:loginVC animated:YES];
ZY_SAFE_RELEASE(loginVC);
}
}
[self.tabBarController presentModalViewController:loginVC animated:**NO**];
I had a similar problem when tried to presentModalViewController (my welcome screen) in main view's viewWillAppear. Is was solved just by moving the modal VC call to viewDidAppear.
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