我們知道在UIKit中做動畫有幾種方法,一種是Animation,還有就是Transition,前者根據對象的屬性產生動畫,後者則是通過View之間的操作完成動畫.

我們可以看一下UIViewAnimationOptions這個類,其中與Transition相關的共有8種選項:

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 }

下面我們UIViewAnimationOptions結構寫一個擴展,這個擴展做2件事:

包含隨機返回8個Transition選項之一的屬性 返回Transition選項對應的名稱

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
        }
    }
}

首先我們在文件范圍建立一個隨機數發生器,我們沒有使用一般的方法,而是使用了iOS9之後才有的新方法,該隨機數發生器,正如其名字那樣返回的隨機數不會重復,除非選完全部可選的隨機數.為什麼不放到結構擴展裡呢?因為我不希望每次讀取RandomDirectionOption屬性都生成一個新的隨機數發生器.

我們在實際的例子中測試一下上面的擴展:

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
                    }
                }
            })

編譯鏈接app,效果如下: