Swift 3/4 How to animate contentMode of UIImageView

问题

My goal is when I click on button to toggle contentMode: scaleAspectFit & scaleAspectFill with animation.

    @IBAction func toggleContentModeAction(_ sender: UIButton) {
    sender.isSelected = !sender.isSelected
    if sender.isSelected {
        UIView.animate(withDuration: 0.3) {
            self.popImageView.contentMode = .scaleAspectFit
            self.view.layoutIfNeeded()
        }
    }else {
        UIView.animate(withDuration: 0.3) {
            self.popImageView.contentMode = .scaleAspectFill
            self.view.layoutIfNeeded()
        }
    }
}

but no effective to my goal. Please fix for me, thanks from Cambodia.

回答1:

The contentMode, itself, is not an animatable property. But you can animated between two different renditions of a view with transition(with:duration:options:animations:completion:), e.g.

@IBAction func didTapButton(_ sender: UIButton) {
    let contentMode: UIViewContentMode = imageView.contentMode == .scaleAspectFill ? .scaleAspectFit : .scaleAspectFill

    UIView.transition(with: imageView, duration: 1, options: .transitionCrossDissolve, animations: {
        self.imageView.contentMode = contentMode
    }, completion: nil)
}

That yields:

来源：https://stackoverflow.com/questions/46701140/swift-3-4-how-to-animate-contentmode-of-uiimageview