Need assistance regarding viewDidLayoutSubviews

问题:

Apple doc regarding viewDidLayoutSubviews says:

When the bounds change for a view controller's view, the view adjusts the positions of its subviews and then the system calls this method. However, this method being called does not indicate that the individual layouts of the view's subviews have been adjusted. Each subview is responsible for adjusting its own layout.

Your view controller can override this method to make changes after the view lays out its subviews. The default implementation of this method does nothing.

I have view1 which contains view2 means view2 is a subview of view1. I am creating a CALayer for my view2 which I want to be exact size of view2. I am using auto layouts so I want to create the CALayer when auto layout finish its work so I can have correct values to set for CALayer frame.

But in viewDidLayoutSubviews method I can't detect when exactly view2 frame is set by auto layout because Apple doc is also saying that

this method being called does not indicate that the individual layouts of the view's subviews have been adjusted.

after that Apple doc saying

Your view controller can override this method to make changes after the view lays out its subviews.

I am so confused at what point auto layout will set view2 frame so I can set my CALayer frame accordingly.

回答1:

As I mentioned in the comments, you don't have to do anything special if your view is aligned with auto layout. If you want a single layer to adjust its bounds to the view's bounds, the most simple and correct way will be overriding layerClass method of the view - in that case layer bounds will be adjusted within a view automatically. If you need one more layer in addition to the standard one, the best place to update layer's bounds may be setFrame: method override.

As of viewDidLayoutSubviews, it is just an event to inform you, that all subviews of viewcontroller's root view are positioned at the desired places. You are not guaranteed that all the rest subviews of those subviews will also be aligned, since it is a responsibility of the parent view itself. they can be both auto layout positioned and manual layout positioned. This event also does not guarantee that all the the views are displayed as desired, especially if their frame change is animated.