iOS – 切换 UIWindow 时的解除分配问题

Question

I use to contextually switch key UIWindow s in my app to provide a bit cleaner flow – Welcome window => Main screen with items list <=> Item container with burger menu and stuff.

Example function follows:

- (void)updateKeyWindow:(UIWindow *)window withTransition:(WindowTransition)transition
{
    UIWindow *originalWindow = _keyWindow;
    _keyWindow = window;

    window.alpha = 0;
    [originalWindow resignKeyWindow];
    [originalWindow resignFirstResponder];
    originalWindow.userInteractionEnabled = NO;
    [window makeKeyAndVisible];
    window.transform = (transition == WindowTransitionFlyDown) ? CGAffineTransformMakeScale(1.02, 1.02) :
                       (transition == WindowTransitionFlyUp)   ? CGAffineTransformMakeScale(.96, .96) :
                                                                 CGAffineTransformIdentity;

//  [UIView animateWithDuration:.24 animations:^{

        window.alpha = 1;
        originalWindow.alpha = 0;
        window.transform = CGAffineTransformIdentity;
        originalWindow.transform = (transition == WindowTransitionFlyDown) ? CGAffineTransformMakeScale(.96, .96) :
                                   (transition == WindowTransitionFlyUp)   ? CGAffineTransformMakeScale(1.02, 1.02) :
                                                                             CGAffineTransformIdentity;

//  } completion:^(BOOL b){

        [originalWindow resignFirstResponder];
        [originalWindow removeFromSuperview];
        [originalWindow.rootViewController.view removeFromSuperview];
        originalWindow.rootViewController = nil;
        originalWindow = nil;

//  }];
}

I use animations to provide nice transitions, but I've commented it out to test if it's not the cause of the issue I have.

The thing is, after dropping originalWindow from the hierarchy and quitting the block/function, the UIWindow is NOT being released and hangs somewhere in the space. I've tested this with child class by putting breakpoint inside overloaded -dealloc .

I've checked both UIApplication 's -keyWindow and AppDelegate 's -window , both having new UIWindow object assigned.

However after tapping anywhere on the screen, the -dealloc for the previous UIWindow is triggered with some -[UITouch dealloc] stuff in the call stack.

I find this behaviour completely weird, there must be something wrong within the UIKit , I'm not expecting there's anything wrong on my side with this approach.

Answer 1

Refer to the resignKeyWindow documentation :

Never call this method directly. The system calls this method and posts UIWindowDidResignKeyNotification to let the window know when it is no longer key...

Try removing that and seeing if it fixes the crash.

Answer 2

The problem is UIApplication's keyWindow is weak by definition. So you should have to connect your UIWindow's strongly on some object; like ApplicationDelegate or some singleton.