Objective-C - When I add a subview, my subview is going out of the screen at the bottom. Misunderstanding of frames?

Question

Im practicing objective-C, and I try to do everything programmatically.

I'm making a simple view that I add on my view of the ViewController, but this subview is going out of the screen. When I set my frame, the position for the X and Y are respected, but the rest, no...

Here is the screenshot of my result :

As you can see... The red subview is going out of the screen.

Here is my loadView where I add that subview :

HomeViewController.m - loadView

-(void)loadView
{
    self.view = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];

    UIView *subview = [[UIView alloc] initWithFrame:CGRectMake(15, 15, self.view.frame.size.width - 30, self.view.frame.size.height - 30)];
    [subview setBackgroundColor:[UIColor redColor]];
    [self.view addSubview:subview];
}

For the padding, I did put 15 for the position x and y... And for the frame, I did calculate with the size of the self.view by removing paddings... As you see, it works well for the width, but for the height, it is a big fail. It goes outside the screen.

In my AppDelegate.h, I set the navigationController.navigationBar.translucent = NO;, in order to that when I set position for x, and y, it starts well after the navigationBar .

I don't understand this weird behavior for the height... If someone has a good explanation for this please.

Thanks

Answer 1

First, you shouldn't rely on the value of self.view in viewDidLoad. It is set to a correct value later, in viewWillAppear:. You can keep your code, if you make your subview resize automatically when self.view is displayed. For that, set autoresizingMask on the subview:

subview.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;

(or add an equivalent set of constraints if you use Auto Layout.)

Also, I recommend to use bounds instead of frame:

UIView *subview = [[UIView alloc] initWithFrame:CGRectMake(15, 15, self.view.bounds.size.width - 30, self.view.bounds.size.height - 30)];

It doesn't make a difference here, but it often does, e.g. if you calculate the frame's x and y based on the parent frame.