Unbalanced calls to begin/end appearance transitio

问题:

While compiling the code i got

"Unbalanced calls to begin/end appearance transitions for <UINavigationController: 0xa98e050>"

warning.

Here is my code

KVPasscodeViewController *passcodeController = [[KVPasscodeViewController alloc] init];
passcodeController.delegate = self;

UINavigationController *passcodeNavigationController = [[UINavigationController alloc] initWithRootViewController:passcodeController];
[(UIViewController *)self.delegate presentModalViewController:passcodeNavigationController animated:YES];

回答1:

I know this is an old question, but for the sake of those who run across this again, here is what I've found.

Firstly, The question does not state where the new viewController was being called.
I suspect this was called from -(void)viewDidLoad

Move the appropriate code to -(void)viewDidAppear: and the problem should go away.

This is because at -viewDidLoad, the view has loaded, but has not yet been presented and the animations and views have not completed.

If your intent is to push a window, do it after the window has been presented and has painted.

If you ever find yourself using timers to control system behavior, ask yourself what you are doing wrong, or how you could do it more properly.

回答2:

I Found that this issue occurs if you trying to push new view controller while previous transaction (animation) in progress.

Anyway, i think, it is presentModalViewController problem, Set animated:NO, may be solve your problem

[(UIViewController *)self.delegate presentModalViewController:passcodeNavigationController animated:NO];

Other option is:

Take NSTimer and call above code between may be 0.50 to 1 second. This also helpful trick. so your pervious viewController has done its animation.

回答3:

This warning appears when you try to load a new viewController before a previously included one is done animating. If your intention is to do that, simply add your code to a dispatch_async(dispatch_get_main_queue() block:

dispatch_async(dispatch_get_main_queue(), ^(void){
        [(UIViewController *)self.delegate presentModalViewController:passcodeNavigationController animated:YES];
});

and the warning will go away.

回答4:

a modern solution may be this:

double delayInSeconds = 0.5;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds *   NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    [self.window.rootViewController presentViewController:yourVC animated:YES completion:nil];
});

回答5:

You did not provide much context, so I assume this error is happening at startup since you are presenting a passcode view controller.

In order to get rid of this warning, I register the app delegate as a delegate of the navigation root view controller:

- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    ((UINavigationController *)self.window.rootViewController).delegate = self;
    return YES;
}

Then I present the modal view controller in navigationController:didShowViewController:animated: with a dispatch_once:

- (void) navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    static dispatch_once_t once;
    dispatch_once(&once, ^{
        KVPasscodeViewController *passcodeController = [[KVPasscodeViewController alloc] init];
        passcodeController.delegate = self;

        UINavigationController *passcodeNavigationController = [[UINavigationController alloc] initWithRootViewController:passcodeController];
        [(UIViewController *)self.delegate presentViewController:passcodeNavigationController animated:YES completion:nil];
    });
}

Since navigationController:didShowViewController:animated: is called after the root view controller did appear, the Unbalanced calls to begin/end appearance transitions warning is gone.