why isn't -layoutSubviews being called?

Question

I'm trying to create a custom layout for some subviews. My file is a ViewController, so I have to refer to its view as self.view. The subviews are subviews of self.view.

When I call [self layoutSubviews]; explicitly in viewDidLoad, it will execute the code in -layoutSubviews without a problem.

However, I've read that I shouldn't call -layoutSubviews explicitly, or call it on self since that's a UIViewController. I tried implementing -setNeedsLayout by calling it like this: [self.view setNeedsLayout] in viewDidLoad, and taking out the explicit call of -layoutSubviews but keeping its declaration. But that didn't seem to work.

I was linked to an article about when layoutSubviews is called and it seems like it should be called when I add subviews, but that doesn't seem to be happening here.

If I want to be safe, and do things the way it suggests in the class reference for UIView and its methods, how should I go about being able to use both methods?

Answer 1

You should never call -layoutSubviews directly. It might be detrimental to performance, but other reasons might as well apply. Instead call -setNeedsLayout. This method sets a flag (or Boolean) that on some next drawing pass the -layoutSubviews method should be called (several methods might set this flag, but it won't force a redraw until the time is right).

Does your -layoutSubviews implementation call -layoutSubviews on the super class?

Perhaps you should show some code so we might help you further with this issue.

Answer 2

There is no such thing as -[UIViewController layoutSubviews] or -[UIViewController setNeedsLayout]. These are UIView methods.

If you want to use the layoutSubviews system, you need to subclass your top-level UIView and implement it there. By default, it does nothing. If you want to layout your views using the view controller, then I would name the methods something else (like layout, since a view controller doesn't have "subviews") to avoid confusion with UIView.

Answer 3

You can have your layout related codes in - (void)viewWillLayoutSubviews method and call [self.viewControllerObject.view setNeedsLayout] where ever you need to layout your subviews of viewControllerObject.

Answer 4

As @Rob Napier answered,

There is no such thing as -[UIViewController layoutSubviews] or -[UIViewController setNeedsLayout]. These are UIView methods.

This is nice, So we are about to subclassing the UIView & assign it as the custom class of the UIViewController's view property. It will work as well, but very lengthy & too much to do for each UIViewController.

There is a easier way (obvious way what we should follow) using the viewWillLayoutSubviews & viewDidLayoutSubviews provided in the UIViewController class.

As the name suggested they are called just before & after, doing the layout thing in the UIView.

Hope these might help Happy coding