如何缩小UITableView滚动的UIImageView内容（图像）？

Question

我想达到这样的效果：

https://cdn.dribbble.com/users/124059/screenshots/3727352/400.gif

为了这个，我正在做：

override func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) { 
    let cell = tableView.dequeueReusableCell(withIdentifier: "CardCell", for: indexPath) as! CardTableViewCell 

    UIView.animate(withDuration: 0.5, delay: 0.3, usingSpringWithDamping: 0.1, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: { 
     cell.coverImageView.transform = CGAffineTransform(scaleX: 0.7, y: 0.7) 
    }, completion: nil) 
} 

但是这个代码调整其大小的UIImageView框架，不是的UIImageView内的图像。

我该如何改进我的代码？

Answer 1

诀窍是弄乱imageView的框架，使其重绘，看起来像内容模式正在改变。你可以这样操纵框架或约束条件，并将其隐藏在另一个视图中。运行示例并让我知道。

import UIKit 

class ViewController: UIViewController { 

    var imageView = UIImageView() 
    var maskView = UIView() 
    var frame : CGRect = .zero 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     // Do any additional setup after loading the view, typically from a nib. 
     view.layoutIfNeeded() 
     imageView = UIImageView(frame: CGRect(x: 20, y: 40, width: view.bounds.width-40, height: view.bounds.height/2)) 
     imageView.image = UIImage(named: "img") 
     imageView.contentMode = .scaleAspectFill 


     maskView = UIView(frame: CGRect(x: 20, y: 40, width: view.bounds.width-40, height: view.bounds.height/2)) 
     maskView.addSubview(imageView) 
     maskView.layer.masksToBounds = true 
     maskView.layer.cornerRadius = 6 
     self.view.addSubview(maskView) 

     //manipulate the imageView to make the content mode seem to change 
     // and have it redraw itself 
     frame = imageView.frame 
     var newFrame = frame 
     newFrame.size.height += newFrame.height 
     imageView.frame = newFrame 
     imageView.center = maskView.center 


     let button = UIButton(frame: CGRect(x: 20, y: maskView.frame.maxY + 60, width: view.bounds.width - 40, height: 40)) 
     button.setTitle("Animate", for: .normal) 
     button.setTitleColor(.blue, for: .normal) 
     button.addTarget(self, action: #selector(ViewController.pressed), for: .touchUpInside) 
     self.view.addSubview(button) 


     let AnotherButton = UIButton(frame: CGRect(x: 20, y: button.frame.maxY + 20, width: view.bounds.width - 40, height: 40)) 
     AnotherButton.setTitle("Reset", for: .normal) 
     AnotherButton.setTitleColor(.blue, for: .normal) 
     AnotherButton.addTarget(self, action: #selector(ViewController.reset), for: .touchUpInside) 
     self.view.addSubview(AnotherButton) 
    } 

    func pressed() { 
     //animate 
     // screw around with the imageView back to the original frame 
     // you could also do this with the height constraints if it was constraint based 
     UIView.animate(withDuration: 1.0, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1.0, options: .curveEaseOut, animations: { 
      self.imageView.frame = self.maskView.bounds 
     }, completion: nil) 

    } 

    func reset() { 
     //reset big frame 
     var newFrame = frame 
     newFrame.size.height += newFrame.height 

     UIView.animate(withDuration: 1.0, delay: 0, usingSpringWithDamping: 1.0, initialSpringVelocity: 1.0, options: .curveEaseOut, animations: { 
      self.imageView.frame = newFrame 
      self.imageView.center = self.maskView.center 
     }, completion: nil) 

    } 

} 

结果：