UIViewAnimationTransition翻转UIImageView

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我在底部被点击的函数中的UIView.transitions第一次工作，但第二次让我的else语句翻转回前端时，每次都会崩溃。获取错误消息“致命错误:在展开可选值时意外发现nil”。每次想要成功翻转前后和后退:)提前感谢各位朋友。;)另外，我在故事板中添加了我的ImageOne和ImageTwo视图！

import UIKit
import Foundation
import Firebase
import FirebaseDatabase

class ViewController: UIViewController {

@IBOutlet weak var mainScrollView: UIScrollView!
@IBOutlet weak var imageOne: UIImageView!
@IBOutlet weak var imageTwo: UIImageView!

var myImageArray = [UIImage]()
var myImageArray2 = [UIImage]()

var back: UIImageView!
var front: UIImageView!

var showingFront = true

override func viewDidLoad() {
    super.viewDidLoad()
    SignedIn()

    self.view.addGestureRecognizer(revealViewController().panGestureRecognizer())

    let singleTap = UITapGestureRecognizer(target: self, action: #selector(ViewController.tapped))
    singleTap.numberOfTapsRequired = 1
    mainScrollView.addGestureRecognizer(singleTap)
    mainScrollView.isUserInteractionEnabled = true

    mainScrollView.frame = view.frame

    myImageArray = [image1, image2 ,image3, image4, image5]
    myImageArray2 = [imageText1, imageText2 ,imageText3, imageText4, imageText5]

    for i in 0..<myImageArray.count {

        front = UIImageView()
        front.image = myImageArray[i]
        front.contentMode = .scaleToFill
        let yPosition = self.view.frame.height * CGFloat(i) + self.view.frame.height/2 - (self.view.frame.height / 1.1)/2
        let xPosition = self.view.frame.width/2 - (self.view.frame.width / 1.1)/2
        front.frame = CGRect(x: xPosition, y: yPosition, width: self.view.frame.width / 1.1, height: self.view.frame.height / 1.1)
        front.layer.borderWidth = 5

        back = UIImageView()
        back.image = myImageArray2[i]
        back.contentMode = .scaleToFill
        back.frame = CGRect(x: xPosition, y: yPosition, width: self.view.frame.width / 1.1, height: self.view.frame.height / 1.1)
        back.layer.borderWidth = 5

        mainScrollView.contentSize.height = mainScrollView.frame.height * CGFloat(i + 1)

        imageOne.addSubview(front)
        imageTwo.addSubview(back)
    }
}

func tapped() {
    print("Hello")
    if (showingFront) {
        UIView.transition(from: imageOne, to: imageTwo, duration: 1, options: UIViewAnimationOptions.transitionFlipFromRight, completion: nil)
        showingFront = false
    } else {
        UIView.transition(from: imageTwo, to: imageOne, duration: 1, options: UIViewAnimationOptions.transitionFlipFromLeft, completion: nil)
        showingFront = true
    }
}

}

Answer 1

你需要添加第二个动画选项来保持"from“视图的效果。我是这样做的：

// declare the animation options
let transitionOptions: UIViewAnimationOptions = [.transitionFlipFromRight, .showHideTransitionViews]

func tapped() {
    print("Hello")
    if (showingFront) {
        UIView.transition(from: imageOne, to: imageTwo, duration: 1, options: transitionOptions, completion: nil)
        showingFront = false
    } else {
        UIView.transition(from: imageTwo, to: imageOne, duration: 1, options: transitionOptions, completion: nil)
        showingFront = true
    }
}

我记得我花了整整一个小时才添加了第二个选项，因为Swift 2代码可以用不同的方式来做。