Swift 3/4如何動畫UIImageView的contentMode

Question

我的目標是當我點擊按鈕切換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() 
     } 
    } 
} 

但對我的目標沒有效果。請爲我修好，感謝柬埔寨。

Answer 1

contentMode本身不是一個動畫屬性。但是您可以在transition(with:duration:options:animations:completion:)的兩個不同的視圖呈現之間進行動畫處理，例如

@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) 
} 

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