IOS实战之自定义转场动画详解

您可以认为，. FullScreen以及其他present风格都是swift为我们实现提供好的，它们是.Custom的特例。而.Custom允许我们更加自由的定义转场动画效果。

UIPresentationController提供了四个函数来定义present和dismiss动画开始前后的操作：

• presentationTransitionWillBegin: present将要执行时
• presentationTransitionDidEnd：present执行结束后
• dismissalTransitionWillBegin：dismiss将要执行时
• dismissalTransitionDidEnd：dismiss执行结束后

  下面的代码简要描述了gif中第三个动画效果的实现原理，您可以在demo的Custom Presentation文件夹下查看完成代码：

   

  
  // 这个相当于fromViewController
  class CustomPresentationFirstViewController: UIViewController {
    // 这个相当于toViewController
    lazy var customPresentationSecondViewController: CustomPresentationSecondViewController = CustomPresentationSecondViewController()
    // 创建PresentationController
    lazy var customPresentationController: CustomPresentationController = CustomPresentationController(presentedViewController: self.customPresentationSecondViewController, presentingViewController: self)
  
    override func viewDidLoad() {
      super.viewDidLoad()
      setupView() // 主要是一些UI控件的布局，可以无视其实现细节
  
      // 设置转场动画代理
      customPresentationSecondViewController.transitioningDelegate = customPresentationController
    }
  
    override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
      // Dispose of any resources that can be recreated.
    }
  
    func animationButtonDidClicked() {
      self.presentViewController(customPresentationSecondViewController, animated: true, completion: nil)
    }
  }
  
  

  重点在于如何实现CustomPresentationController这个类：

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