Swift：关闭在当前上下文中显示图片的 ViewController 时不时冻结屏幕答案

【问题标题】：Swift: Screen Freezing from time to time when Dismissing a ViewController displaying a picture over the current contextSwift：关闭在当前上下文中显示图片的 ViewController 时不时冻结屏幕
【发布时间】：2017-12-12 20:22:54
【问题描述】：

我遇到了一些问题：当关闭在当前上下文中显示图片的 ViewController 时，屏幕不时冻结。

有人可以提供一些关于如何解决此问题的见解吗？

我的代码示例如下：

导入 UIKit

类 ViewControllerCell: UICollectionViewCell {

override init(frame: CGRect) {
    super.init(frame: frame)

    backgroundColor = UIColor.white

    addSubview(showPhotoButton)

    showPhotoButton.leftAnchor.constraint(equalTo: leftAnchor, constant: 200).isActive = true
    showPhotoButton.bottomAnchor.constraint(equalTo: topAnchor, constant: 160).isActive = true
    showPhotoButton.heightAnchor.constraint(equalToConstant: 50).isActive = true
    showPhotoButton.widthAnchor.constraint(equalToConstant: 70).isActive = true

}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}


lazy var showPhotoButton: UIButton = {
    let button = UIButton(type: .system)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.setTitle("Show", for: .normal)
    button.addTarget(self, action: #selector(showSale), for: .touchUpInside)
    button.setTitleColor(UIColor(r: 120, g: 80, b: 255), for: .normal)
    return button
}()


@objc func showSale() {
    let popupViewController = PopupViewController()
    popupViewController.modalPresentationStyle = .overCurrentContext
    popupViewController.modalTransitionStyle = UIModalTransitionStyle.crossDissolve
    window!.rootViewController?.present(PopupViewController, animated: true, completion: nil)
}

}

导入 UIKit

类 SalePopupViewController: UIViewController {

override func viewDidLoad() {
    view.backgroundColor = UIColor(white: 1, alpha: 0.60)
    view.isOpaque = false

    view.addSubview(rebateImage)
    view.addSubview(dismissButton)

    dismissButton.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
    dismissButton.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
    dismissButton.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
    dismissButton.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true

    rebateImage.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    rebateImage.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: -35).isActive = true
    rebateImage.heightAnchor.constraint(equalToConstant: 290).isActive = true
    rebateImage.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1).isActive = true


}

let dismissButton: UIButton = {
    let button = UIButton(type: .system)
    button.addTarget(self, action: #selector(dismissPopup), for: .touchUpInside)
    button.translatesAutoresizingMaskIntoConstraints = false
    return button
}()

let rebateImage: UIImageView = {
    let image = UIImageView()
    image.translatesAutoresizingMaskIntoConstraints = false
    image.layer.masksToBounds = false
    image.layer.cornerRadius = 2
    image.contentMode = .scaleAspectFill
    image.clipsToBounds = true
    image.image = UIImage(named: "SaleCostco")
    return image
}()

@objc func dismissPopup() {

    DispatchQueue.global(qos: .userInitiated).async {
        DispatchQueue.main.async {
            self.dismiss(animated: true, completion: nil)
        }
    }


}

}

【问题讨论】：

调试提示：当屏幕冻结时，在 Xcode 的调试器中暂停应用并检查主线程上发生的情况。
在不使 self 变弱的情况下异步执行诸如关闭之类的 UI 操作会带来很多问题，我建议始终根据情况执行 [unowned self] 的 [weak self]（在这种情况下，weak self 就足够了) 然后将 self.dismiss 称为 self?.dismiss。顺便说一句，为什么您需要先分配到全局队列然后再返回主队列？好像没必要
感谢您的帮助！问题已解决！

标签： ios swift uiviewcontroller uicollectionviewcell photo

【解决方案1】：

您的异步代码没有意义。您分派到全局队列，然后立即返回主线程。尝试简单地将 dismissPopup() 的实现更改为：

@objc func dismissPopup() {
   dismiss(animated: true, completion: nil)
}

【讨论】：

感谢您的帮助！