UIKit视图动画的微扩展

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我们知道在UIKit中做动画有几种方法,一种是Animation,还有就是Transition,前者根据对象的属性产生动画,后者则是通过View之间的操作完成动画.

我们可以看一下UIViewAnimationOptions这个类,其中与Transition相关的共有8种选项:

public static var TransitionNone: UIViewAnimationOptions { get } // default
    public static var TransitionFlipFromLeft: UIViewAnimationOptions { get }
    public static var TransitionFlipFromRight: UIViewAnimationOptions { get }
    public static var TransitionCurlUp: UIViewAnimationOptions { get }
    public static var TransitionCurlDown: UIViewAnimationOptions { get }
    public static var TransitionCrossDissolve: UIViewAnimationOptions { get }
    public static var TransitionFlipFromTop: UIViewAnimationOptions { get }
    public static var TransitionFlipFromBottom: UIViewAnimationOptions { get }

下面我们UIViewAnimationOptions结构写一个扩展,这个扩展做2件事:

1. 包含随机返回8个Transition选项之一的属性
2. 返回Transition选项对应的名称

import Foundation
import UIKit
import GameplayKit

@available(iOS 9.0, *)
private let randomGen:GKShuffledDistribution = GKShuffledDistribution(forDieWithSideCount: UIViewAnimationOptions.allDirectionOptions.count)

@available(iOS 4.0, *) extension UIViewAnimationOptions{
    static let allDirectionOptions:[UIViewAnimationOptions] = [.TransitionNone,.TransitionFlipFromLeft,.TransitionFlipFromRight,.TransitionCurlUp,.TransitionCurlDown,.TransitionCrossDissolve,.TransitionFlipFromTop,.TransitionFlipFromBottom]

    var optionName:String{
        switch self.rawValue {
        case UIViewAnimationOptions.TransitionNone.rawValue:
            return "TransitionNone"
        case UIViewAnimationOptions.TransitionFlipFromBottom.rawValue:
            return "TransitionFlipFromBottom"
        case UIViewAnimationOptions.TransitionFlipFromTop.rawValue:
            return "TransitionFlipFromTop"
        case UIViewAnimationOptions.TransitionCrossDissolve.rawValue:
            return "TransitionCrossDissolve"
        case UIViewAnimationOptions.TransitionCurlDown.rawValue:
            return "TransitionCurlDown"
        case UIViewAnimationOptions.TransitionCurlUp.rawValue:
            return "TransitionCurlUp"
        case UIViewAnimationOptions.TransitionFlipFromRight.rawValue:
            return "TransitionFlipFromRight"
        case UIViewAnimationOptions.TransitionFlipFromLeft.rawValue:
            return "TransitionFlipFromLeft"
        default:
            return "noneName"
        }
    }
    /*
    @available(iOS 9.0, *)
    private lazy var randomGen:GKShuffledDistribution = {
        return GKShuffledDistribution(forDieWithSideCount: allDirectionOptions.count)
    }()
    */
    static var RandomDirectionOption:UIViewAnimationOptions {
        if #available(iOS 9.0, *) {
            let idx = randomGen.nextInt() - 1
            print("gen is \(randomGen) , idx is \(idx)")
            return allDirectionOptions[idx]
        } else {
            return .TransitionNone
        }
    }
}

首先我们在文件范围建立一个随机数发生器,我们没有使用一般的方法,而是使用了iOS9之后才有的新方法,该随机数发生器,正如其名字那样返回的随机数不会重复,除非选完全部可选的随机数.为什么不放到结构扩展里呢?因为我不希望每次读取RandomDirectionOption属性都生成一个新的随机数发生器.

我们在实际的例子中测试一下上面的扩展:

let option = UIViewAnimationOptions.RandomDirectionOption
        UIView.transitionWithView(status, duration: 0.33, options: [.CurveEaseOut,option], animations: {
                self.status.hidden = false
                self.label.text = option.optionName
                self.transitionName.text = option.optionName
                self.transitionName.sizeToFit()
                self.transitionName.center = CGPoint(x: self.statusPosition.x, y: self.transitionName.center.y)
            }, completion: {_ in
                delay(seconds: 2.0){
                    if index < self.messages.count - 1{
                        self.removeMessage(index: index)
                    }else{
                        //reset form
                    }
                }
            })

编译链接app,效果如下: