更改视图控制器时保持滚动位置

Question

我有一个带有自定义表格视图的食谱应用。问题是，当进入配方视图控制器并返回配方列表视图控制器时，它不会保持先前的滚动位置。它总是回到顶部。

我想知道这是否是我的代码中的某些内容，或者是否是我需要添加的内容以保持以前的位置。

这是我的食谱列表视图控制器的完整代码：

var recipeImgs: [UIImage] = [UIImage(named: "bananaPancakesCat.jpg")!,UIImage(named: "blackEyedPeaPattiesCat.jpg")!,UIImage(named: "blueberryMuffinsCat.jpg")!, UIImage(named: "buckwheatWafflesCat.jpg")!, UIImage(named: "cashewCreamCheeseCat.jpg")!, UIImage(named: "frenchToastCat.jpg")!, UIImage(named: "fruitSyrupCat.jpg")!, UIImage(named: "hashBrownsCat.jpg")!, UIImage(named: "proteinBarsCat.jpg")!, UIImage(named: "smoothieCat.jpg")!, UIImage(named: "tempehBaconCat.jpg")!, UIImage(named: "tofuQuicheCat.jpg")!]

override func viewDidLoad() {
    super.viewDidLoad()
    tableView.delegate = self
    tableView.dataSource = self
}

override func viewDidDisappear(_ animated: Bool) {
    self.tableView.removeFromSuperview()
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if let cell = tableView.dequeueReusableCell(withIdentifier: "RecipesTableViewCell") as? RecipesTableViewCell {
        cell.configureCell(recipeImgs[(indexPath as NSIndexPath).row])
        return cell

    } else {
        return RecipesTableViewCell()
    }

}

func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    if (UIDevice.current.userInterfaceIdiom == .pad) {
        return 120
    }
        return 90.0
}

func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return recipeImgs.count
}

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    if (indexPath as NSIndexPath).row == 0 {
        performSegue(withIdentifier: "BRVC1", sender: self)
    } else if (indexPath as NSIndexPath).row == 1 {
        performSegue(withIdentifier: "BRVC2", sender: self)
    } else if (indexPath as NSIndexPath).row == 2 {
        performSegue(withIdentifier: "BRVC3", sender: self)
    } else if (indexPath as NSIndexPath).row == 3 {
        performSegue(withIdentifier: "BRVC4", sender: self)
    } else if (indexPath as NSIndexPath).row == 4 {
        performSegue(withIdentifier: "BRVC5", sender: self)
    } else if (indexPath as NSIndexPath).row == 5 {
        performSegue(withIdentifier: "BRVC6", sender: self)
    } else if (indexPath as NSIndexPath).row == 6 {
        performSegue(withIdentifier: "BRVC7", sender: self)
    } else if (indexPath as NSIndexPath).row == 7 {
        performSegue(withIdentifier: "BRVC8", sender: self)
    } else if (indexPath as NSIndexPath).row == 8 {
        performSegue(withIdentifier: "BRVC9", sender: self)
    } else if (indexPath as NSIndexPath).row == 9 {
        performSegue(withIdentifier: "BRVC10", sender: self)
    } else if (indexPath as NSIndexPath).row == 10 {
        performSegue(withIdentifier: "BRVC11", sender: self)
    } else {
        performSegue(withIdentifier: "BRVC12", sender: self)
    }
}

还有一个视频来演示正在发生的事情：https://www.dropbox.com/s/g6jy37t97d1ihft/ScreenRecording_09-19-2017%2015%3A31.mp4?dl=0

Answer 1

向视图控制器添加一个变量来跟踪滚动视图的内容偏移量。在viewWillDisappear方法中设置该变量，并在viewWillAppear方法中调用UITableView的setContentOffset方法：

private var contentOffset: CGPoint?

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    if let contentOffset = self.contentOffset {
        self.tableView.setContentOffset(contentOffset, animated: true)
    }
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)

    self.contentOffset = self.tableView.contentOffset
}