Question

I have a UIModalTransitionStylePartialCurl which is acting funky. My views UILabel and UIButton animate as if the labels frame is being changed all the time.

In iOS 4 or 6 it works statically. I’ve made a video of the bug on youtube.

I found an answer to this problem, but I don’t quite understand the implementation. I alloc and init all of my elements in viewDidLoad, so where exactly is [self layoutIfNeeded]; going to help?

My code, if relevant is as follows (refactored):

- (void)viewDidLoad
{
[super viewDidLoad];


// Label
textLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 120, 280, 40)];
textLabel.text = @"Change password";
[self.view addSubview: textLabel];

// old password
oldPassword = [[UITextField alloc] initWithFrame: CGRectMake(20, 180, 280, 40)];
oldPassword.secureTextEntry = YES;
oldPassword.placeholder = @"Current Password";
oldPassword.returnKeyType = UIReturnKeyNext;
oldPassword.autocapitalizationType = UITextAutocapitalizationTypeNone;
oldPassword.delegate = self;
[self.view addSubview: oldPassword];

// New password
CGRect chosenPasswordFrame = oldPassword.frame;
chosenPasswordFrame.origin.y += 40;
chosenPassword = [[CustomTextField alloc] initWithFrame: chosenPasswordFrame];
chosenPassword.secureTextEntry = YES;
chosenPassword.placeholder = @"New Password";
chosenPassword.returnKeyType = UIReturnKeyGo;
chosenPassword.autocapitalizationType = UITextAutocapitalizationTypeNone;
chosenPassword.delegate = self;
[self.view addSubview: chosenPassword];

// Submit button
submitButton = [[UIButton alloc] initWithFrame:CGRectMake(20, chosenPasswordFrame.origin.y + chosenPasswordFrame.size.height + 20, self.view.frame.size.width - 40, 45)];
[submitButton setTitle:@"Submit" forState:UIControlStateNormal];
[submitButton addTarget:self action:@selector(changePassword) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview: submitButton];

self.view.backgroundColor = [UIColor colorWithPatternImage:[[AppTheme sharedTheme] changePasswordBackgroundImage]];

}

Answer 1

It looks like the setting of your view’s frames is getting caught in the CATransaction being created by the partial page curl animation and being animated. Since the frames should never have been CGRectZero at least in the code you posted, this does seem to be a bug in iOS 5. Especially based on the number of up-votes that the answer you linked has received. And that answer describes the problem well.

Essentially, if you force the new view to lay itself out immediately by calling [self layoutIfNeeded] it forces the view system to realize that these are the current frame values not the ones to be animated to. And then even if this bug still tries to animate it’s a non-op. Animating from frame A to frame A is at the very worst imperceptible. And since the “buggy” animation would finish at the same time as the curl animation it really (in practice) doesn’t matter to you. With the exception of an inexplicable call to layoutIfNeeded in viewDidLoad.