UIViewController viewDidLayoutSubviews called when transforming a subview - objective-c

Question

I have the following use case:
a view controller (RotationVC) that contains a bit of logic, among others, rotating one of the subviews (by setting its transform to CGAffineTransformMakeRotation)
this RotationVC overrides the viewDidLayoutSubviews method to set its subviews to be as big as the parent view (self.view)
(creating the view controllers and its views is all done programmatically and it has to stay this way; I tried using autoresizingMask with flexible width and flexible height on the subviews but it didn't work)
another view controller (ParentVC) adds the RotationVC as its child, adds its view as its subview and sets its frame at some point to be square - the idea is that when the frame is set, RotationVC viewDidLayoutSubviews will be called and set the subviews to correct sizes (which actually works fine), and then all works fine
(the RotationVC will be used in other view controllers as well and will have different sized, that's the reason it has been extracted to a 'child' view controller and its size should be flexible)
Well, it doesn't work correctly. The problem is that after each rotation, RotationVC viewDidLayoutSubviews method is called, which sets the rotated views frame. This is wrong, as according to Apple's documentation, using the frame property is wrong when the view's transform is anything else than identity (as is in this case). As a result, the rotated view is 'skewed'. Here is the source code down to the delegate, you should be able to paste it to a single file and run. In case you do, what I'm trying to achieve is for the rotated subview to preserve its shape (in this example it's a rectangle):
#import "AppDelegate.h"
#interface RotationVC : UIViewController
#property (nonatomic, weak) UIView *background;
#property (nonatomic, weak) UIView *foreground;
#property (nonatomic) int degrees;
#end
static const double DURATION = 0.5;
#implementation RotationVC
- (void)viewDidLoad {
[super viewDidLoad];
UIView *tmp = [UIView new];
self.background = tmp;
self.background.layer.borderWidth = 2;
self.background.layer.borderColor = [UIColor redColor].CGColor;
[self.view addSubview:self.background];
tmp = [UIView new];
self.foreground = tmp;
self.foreground.layer.borderWidth = 2;
self.foreground.layer.borderColor = [UIColor blueColor].CGColor;
[self.view addSubview:self.foreground];
}
- (void)viewDidLayoutSubviews {
[super viewDidLayoutSubviews];
self.background.frame = self.view.bounds;
CGAffineTransform tmp = self.foreground.transform;
self.foreground.transform = CGAffineTransformIdentity;
self.foreground.frame = self.view.bounds;
self.foreground.transform = tmp;
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[self performSelector:#selector(rotate) withObject:self];
}
- (void)rotate {
self.degrees = (self.degrees + 15) % 360;
[UIView animateWithDuration:DURATION
delay:0
options:UIViewAnimationOptionCurveLinear|UIViewAnimationOptionBeginFromCurrentState
animations:^{
self.foreground.transform = CGAffineTransformMakeRotation(self.degrees * M_PI/180);
}
completion:^(BOOL finished) {
[self performSelector:_cmd withObject:self afterDelay:0];
}];
}
#end
#interface ParentVC : UIViewController
#property (nonatomic, weak) RotationVC *rotationVC;
#end
#implementation ParentVC
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
RotationVC *tmp = [RotationVC new];
self.rotationVC = tmp;
[self addChildViewController:self.rotationVC];
[self.rotationVC didMoveToParentViewController:self];
}
return self;
}
- (void)viewDidLoad {
[super viewDidLoad];
[self.view addSubview:self.rotationVC.view];
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
self.rotationVC.view.bounds = CGRectMake(0, 0, 100, 100);
self.rotationVC.view.center = self.view.center;
}
#end
#implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
UINavigationController *navi = [[UINavigationController alloc] initWithRootViewController:[ParentVC new]];
navi.navigationBarHidden = YES;
self.window.rootViewController = navi;
[self.window makeKeyAndVisible];
return YES;
}
#end
There is a hack that works - in the viewDidLayoutSubviews method, store the rotated view's transform to a temp variable, set the view's transform to identity, set the frame, and set it to rotation again - this is ugly as hell and I bet there has to be a better way. I was also able to devise a few other workarounds, but each one was uglier than the previous one...
Would anybody have a hint as to what to do in this case?

Answer 1

I was able to solve the issue. Just use the following code:
self.foreground.bounds = self.view.bounds;
self.foreground.center = self.background.center;
instead of setting the frame.
This is explained in https://developer.apple.com/library/ios/documentation/windowsviews/conceptual/viewpg_iphoneos/WindowsandViews/WindowsandViews.html#//apple_ref/doc/uid/TP40009503-CH2-SW7:
Important: If a view’s transform property is not the identity transform, the value of that view’s frame property is undefined and must be ignored. When applying transforms to a view, you must use the view’s bounds and center properties to get the size and position of the view. The frame rectangles of any subviews are still valid because they are relative to the view’s bounds.
I always thought that setting the frame is setting the bounds and the center at the same time, but apparently this is very untrue.