swift UIView 过渡不翻转视图

Question

UIView.transition does not work with a view as a subview

I have the following simple set up:

func flipYellowSubView(imageView: UIImageView) {
        let yellowSubView = UIView(frame: imageView.frame)
        yellowSubView.backgroundColor = .yellow
        imageView.addSubview(yellowSubView)
        UIView.transition(with: yellowSubView, duration: 0.5, options: [.transitionFlipFromBottom], animations: {
        }, completion: { (finished: Bool) in
            if finished {
                yellowSubView.removeFromSuperview()
            }
        })
    }

So if I pass an imageView to flipYellowSubView, I expect the yellowSubview to be added, flipped and then removed.

What happens is that the flipYellowSubView is added and removed, but no flipping happens.

Answer 1

You can try the code that follows:

func flipYellowSubView(imageView: UIImageView) {
    let yellowSubView = UIView(frame: imageView.frame)
    yellowSubView.backgroundColor = .yellow

    imageView.addSubview(yellowSubView)
    UIView.animate(withDuration: 1, animations: {
        yellowSubView.transform = CGAffineTransform(scaleX: 1, y: -1)
    }) { (finished) in
        yellowSubView.removeFromSuperview()
    }
}

The above transition doesn't work if called in a view which was just added. If you had the view already in your hierarchy and loaded before, it did work.

Instead of using a transition you can use UIView.animate and transform y scale to get desired result.

Hope it helps.