前言

开发时经常会自定义一些弹出视图，比如弹框（Alert）、底部弹出框(Action Sheet)等。自定义弹出视图有许多方法，到底哪种才更正确呢？下面我列举几种方法，一起讨论。先附上我的方案https://github.com/CatchZeng/SwiftPopup

addSubview

顾名思义，就是造出一个View，然后add到ViewController的View上显示出来，如https://www.jianshu.com/p/de2ecfd770c2的做法。

• 好处：够简单
• 坏处：视图&逻辑都在View上，职能不清晰，扩展性差，显示依赖于ViewController

addChildViewController

使用addChildViewController方法，将视图显示出来。如https://www.jianshu.com/p/6d790e6eb2ba的做法。

• 好处：简单、职能清晰...
• 坏处：在导航栏控制器或者标签栏控制器下弹出，会出现没完全覆盖到的情况。

window

新建一个window，切换成KeyWindow，将弹出视图作为rootViewController。代码如下

func show() {
  previousWindow = UIApplication.shared.keyWindow
  keyWindow = UIWindow(frame: UIScreen.main.bounds)
  keyWindow?.rootViewController = self
  keyWindow?.windowLevel = UIWindowLevelNormal + 100
  keyWindow?.backgroundColor = UIColor.clear
  keyWindow?.makeKeyAndVisible()
}

• 好处：简单、职能清晰...
• 坏处：在横屏的时候，第二次弹出时，出现显示问题【暂时不知道为什么】

第二次显示问题

UIPresentationController

使用UIPresentationController自定义转场动画，这也是我的实现方法。
UIPresentationController是提供高级视图切换的类。它让管理present ViewController的过程变得简单。

Presentation

如下图弹出一个UIViewController，可以和用户交互的Controller叫做PresentedViewController，而后面那个被部分遮挡的UIViewController叫做PresentingViewController.

Presentation

UIPopoverController的使用方法

• 设置style&delegate

 modalPresentationStyle = .custom
 transitioningDelegate = self

• 实现delegate，此代理需要UIPresentationController，以及UIViewControllerAnimatedTransitioning来自定义转场的动画

extension SwiftPopup: UIViewControllerTransitioningDelegate {
    
    public func presentationController(forPresented presented: UIViewController,
                                       presenting: UIViewController?,
                                       source: UIViewController) -> UIPresentationController? {
        let controller = SwiftPopupPresentationController(presentedViewController: presented,
                                                       presenting: presenting)
        controller.backViewColor = backViewColor
        
        return controller
    }
    
    public func animationController(forPresented presented: UIViewController,
                                    presenting: UIViewController,
                                    source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return showAnimation
    }
    
    public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return dismissAnimation
    }
}

• 实现自定义的UIPresentationController

open class SwiftPopupPresentationController: UIPresentationController {
    // MARK: Override Methods 

    // 将要开始转场
    override open func presentationTransitionWillBegin() {
    }

    // 将要移除页面
    override open func dismissalTransitionWillBegin() {
    }
    
   // 是否要移除PresentersView，也就是转场之前的视图，这里为false，因为弹框需要看到之前的视图
    override open var shouldRemovePresentersView: Bool {
        return false
    }

• 实现自定义的动画

open class SwiftPopupShowAnimation: NSObject, UIViewControllerAnimatedTransitioning {
    
    public var duration: TimeInterval = 0.8
    public var delay: TimeInterval = 0.0
    public var springWithDamping: CGFloat = 0.8
    public var springVelocity: CGFloat = 2.0
    
    open func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return duration
    }
    
    open func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let toViewController = transitionContext.viewController( forKey: UITransitionContextViewControllerKey.to),
            let toView = transitionContext.view( forKey: UITransitionContextViewKey.to)
            else {
            return
        }
        
        let containerView = transitionContext.containerView
        toView.frame = transitionContext.finalFrame(for: toViewController)
        containerView.addSubview(toView)
        
        toView.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)
        UIView.animate(withDuration: duration,
                       delay: delay,
                       usingSpringWithDamping: springWithDamping,
                       initialSpringVelocity: springVelocity,
                       options: .curveEaseInOut, animations: {
                        toView.transform = CGAffineTransform(scaleX: 1.0, y: 1.0)
        }) { (finished) in
            transitionContext.completeTransition(finished)
        }
    }
}

• Show

public func show(above viewController: UIViewController? = UIApplication.shared.keyWindow?.rootViewController,
                           completion: (()-> Void)? = nil) {
        mIsShowing = true
        
        viewController?.present(self, animated: true, completion: completion)
    }

• Dismiss

public func dismiss(completion: (()-> Void)? = nil) {
        dismiss(animated: true) {
            self.mIsShowing = false
            completion?()
        }
    }

完整代码 https://github.com/CatchZeng/SwiftPopup

Demo

小结

如遇问题或者有更好的方式，欢迎加QQ群讨论：157672725