iOS8每日一技：深入解析Presentation Controllers-优快云博客

iOS8每日一技：深入解析Presentation Controllers

iOS8-day-by-day Selection of projects accompanying the iOS8-Day-by-Day blog series 项目地址: https://gitcode.com/gh_mirrors/io/iOS8-day-by-day

前言

在iOS8中，苹果引入了UIPresentationController这一全新概念，彻底改变了视图控制器呈现的管理方式。本文将基于ScottLogic的iOS8-day-by-day项目，深入探讨Presentation Controllers的工作原理、实现方法及其在自适应布局中的应用。

什么是Presentation Controller？

基本概念

UIPresentationController是iOS8引入的一个新类，负责管理视图控制器的整个呈现过程。每当一个视图控制器出现在屏幕上时，UIKit都会使用一个Presentation Controller来管理其呈现方式。

与传统方式的区别

在iOS7及之前版本中，视图控制器过渡动画需要处理所有视图层次结构的变化，包括背景视图、遮罩层等。这种设计导致职责不清晰，代码难以维护。iOS8通过引入Presentation Controller，将视图层次管理的职责明确分离：

动画控制器：专注于视图控制器内容的过渡动画
呈现控制器：管理其他所有视图的呈现和布局

创建自定义Presentation Controller

基本实现步骤

创建UIPresentationController的子类
重写关键生命周期方法
实现自定义呈现逻辑

核心代码示例

class OverlayPresentationController: UIPresentationController {
    let dimmingView = UIView()
    
    override init(presentedViewController: UIViewController, 
                presenting presentingViewController: UIViewController?) {
        super.init(presentedViewController: presentedViewController, 
                 presenting: presentingViewController)
        dimmingView.backgroundColor = UIColor(white: 0.0, alpha: 0.5)
    }
    
    override func presentationTransitionWillBegin() {
        dimmingView.frame = containerView?.bounds ?? CGRect.zero
        dimmingView.alpha = 0.0
        containerView?.insertSubview(dimmingView, at: 0)
        
        presentedViewController.transitionCoordinator?.animate(alongsideTransition: { _ in
            self.dimmingView.alpha = 1.0
        }, completion: nil)
    }
    
    override func dismissalTransitionWillBegin() {
        presentedViewController.transitionCoordinator?.animate(alongsideTransition: { _ in
            self.dimmingView.alpha = 0.0
        }, completion: { _ in
            self.dimmingView.removeFromSuperview()
        })
    }
    
    override func frameOfPresentedViewInContainerView() -> CGRect {
        return containerView?.bounds.insetBy(dx: 30, dy: 30) ?? CGRect.zero
    }
}

关键方法解析

presentationTransitionWillBegin()：
- 在呈现过渡即将开始时调用
- 设置并添加遮罩视图
- 使用过渡协调器实现平滑动画
dismissalTransitionWillBegin()：
- 在消失过渡即将开始时调用
- 淡出遮罩视图并在完成后移除
frameOfPresentedViewInContainerView()：
- 定义被呈现视图的frame
- 本例中使视图四周各缩进30点

使用自定义Presentation Controller

配置过渡代理

要使自定义Presentation Controller生效，需要实现UIViewControllerTransitioningDelegate协议：

class OverlayTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {
    func presentationController(forPresented presented: UIViewController, 
                              presenting: UIViewController?, 
                              source: UIViewController) -> UIPresentationController? {
        return OverlayPresentationController(presentedViewController: presented, 
                                          presenting: presenting)
    }
}

两种使用方式

1. 代码方式呈现

let overlayTransitioningDelegate = OverlayTransitioningDelegate()

func presentViewControllerProgrammatically() {
    let overlayVC = storyboard?.instantiateViewController(withIdentifier: "overlayViewController")
    prepareOverlayVC(overlayVC)
    present(overlayVC, animated: true)
}

private func prepareOverlayVC(_ overlayVC: UIViewController) {
    overlayVC.transitioningDelegate = overlayTransitioningDelegate
    overlayVC.modalPresentationStyle = .custom
}

2. Storyboard Segue方式呈现

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "bouncySegue" {
        let overlayVC = segue.destination
        prepareOverlayVC(overlayVC)
    }
}

自适应布局支持

处理设备旋转

自定义Presentation Controller需要正确处理设备旋转等布局变化：

override func containerViewWillLayoutSubviews() {
    super.containerViewWillLayoutSubviews()
    dimmingView.frame = containerView?.bounds ?? CGRect.zero
    presentedView?.frame = frameOfPresentedViewInContainerView
}

自适应策略

有三种主要方式处理布局变化：

使用Auto Layout约束：为遮罩视图添加约束
重写viewWillTransitionToSize：响应尺寸变化
重写containerViewWillLayoutSubviews：直接调整frame

自定义过渡动画

实现动画控制器

class BouncyViewControllerAnimator: NSObject, UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.8
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let presentedView = transitionContext.view(forKey: .to) else { return }
        
        let center = presentedView.center
        presentedView.center = CGPoint(x: center.x, y: -presentedView.bounds.height)
        transitionContext.containerView.addSubview(presentedView)
        
        UIView.animate(withDuration: transitionDuration(using: transitionContext),
                      delay: 0,
                      usingSpringWithDamping: 0.6,
                      initialSpringVelocity: 10.0,
                      options: [],
                      animations: {
                          presentedView.center = center
                      },
                      completion: { _ in
                          transitionContext.completeTransition(true)
                      })
    }
}

更新过渡代理

func animationController(forPresented presented: UIViewController, 
                        presenting: UIViewController, 
                        source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    return BouncyViewControllerAnimator()
}