UIViewAutoresizingMask expands subview width beyond superview's bounds

Question

I need to show some people what it was like before Autolayout, so I wanted to try autoresizing masks to build a view that looks like this:

 ————————————
|  ————————  |
| |  red   | |
| |        | |
|  ————————  |
|            |
|   yellow   |
 ————————————

I want the red UIView to expand horizontally but to keep its left, top, and right margins at 20 points when the device is rotated.

Here's my code:

// .h

@interface NextViewController : UIViewController

@end

// .m

@interface NextViewController ()

@property (nonatomic) UIView *rectView;

@end

@implementation NextViewController

- (void)loadView {
    self.view = [[UIView alloc] initWithFrame:CGRectZero];
    self.view.backgroundColor = [UIColor yellowColor];

    // 280 width for iPhone 5S when left and right paddings are 20 points
    self.rectView = [[UIView alloc] initWithFrame:CGRectMake(20, 20, 280, 100)];
    [self.view addSubview:self.rectView];
    self.rectView.backgroundColor = [UIColor redColor];
    self.rectView.autoresizingMask = UIViewAutoresizingFlexibleWidth;
}

@end

My problem is that the red UIView always goes beyond the yellow UIView's width:

I printed the red view's description:

Printing description of $15:
<UIView: 0x7fc360e181c0; frame = (20 20; 600 100); autoresize = W; layer = <CALayer: 0x600000226960>>

So what am I doing wrong?

Answer 1

Ah, I get it now. It's this line:

self.view = [[UIView alloc] initWithFrame:CGRectZero];

The subviews' autoresizing masks are being evaluated against this CGRectZero frame of the top-level view which is why they aren't being resized correctly. I gave it the frame of an iPhone 5S screen on portrait mode instead, and that fixed the rotation scaling:

self.view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 568)];