Where to get frame size of custom UIView in its su

问题:

When does the correct frame size of the UIView is calculated when I add my custom UIView by using storyboard? I can't get correct frame size in UIView's init(frame: CGRect) or init(coder aDecoder: NSCoder) or awakeFromNib(). I get the correct size in override func layoutSubviews() but this time the view is not added to the view controller's view.

Edit:
I want to do this in the UIView subclass because I add a CAGradientLayer layer (which has same size with my view) to my custom UIView. There must be a better way than setting up the view in UIViewControllers viewDidLayoutSubviews method.

There are two vertical constraints (trailing and leading space to superview) that adjust the width of my custom view. But the width is 600 in the mentioned methods, not the screen width.

回答1:

func viewWillAppear(_ animated: Bool)

This is called on the viewController after the view hierarchy is in place and the geometry is set up.

It is usually the best place to arrange geometry-dependent viewController code, and is called just before transition animations are run.

It is followed by a call to viewDidAppear which is called after transition animations have completed.

update

as you want to set this directly in a custom view (rather than in the viewController) the appropriate UIView function to override is layoutSubviews. Be sure to call super.layoutSubviews() in the override.

override func layoutSubviews() {
    super.layoutSubviews()
    //self.frame will be correct here
}

This will be called after the viewController's viewWillAppear and before viewDidAppear

update 2: collectionView cells Collection view cells get their frame data from the collectionview's layout. When a cell needs to know it's geometry, you can override applyLayoutAttributes

func applyLayoutAttributes(_ layoutAttributes: UICollectionViewLayoutAttributes!)

One of the default layoutAttributes is the frame property. See also my comment below on how to extract the frame directly from collectionView.layout.

回答2:

Since viewDidLayoutSubviews() is getting called multiple times, I'd recommend using the viewDidAppear() delegate.

viewDidLoad() is called before any frame was set.

viewDidLayoutSubviews() is called during frame sizing and will be called multiple times with different frame sizes (usually frameZero before a frame is calculated).

viewDidAppear() All frames are set.

回答3:

You should have an IBOutlet to your UIView and in the viewDidLayoutSubviews() method, get the size by yourViewOutlet.frame.size.