尝试在 UIImageView 中的图像之间淡入淡出时出现白屏

Question

我试图通过使用 UIImageView 并通过设置过渡动画来在两个图像之间平滑过渡，但似乎过渡没有按预期进行，因为出现了白屏而不是新图像淡入。

我用了作为参考，不知道哪里出错了:(

class ViewController: UIViewController {

    var bckgImageView = UIImageView(image: UIImage(named: "one"))

    override func viewDidLoad() {
        super.viewDidLoad()

        bckgImageView.frame = self.view.frame
        self.view.addSubview(bckgImageView)

        animateBackground()

    }

    func animateBackground() {

        UIView.transition(with: self.view,
                          duration: 5,
                          options: .transitionCrossDissolve,
                          animations: { self.bckgImageView.image = UIImage(named: "two") },
                          completion: nil)

    }

Answer 1

在 viewDidLoad 中尚未计算 AutoLayout

您可以在viewDidLayoutSubviews 中更改布局时设置框架。试试这个

class ViewController: UIViewController {

    var bckgImageView = UIImageView(image: UIImage(named: "one"))

    override func viewDidLoad() {
        super.viewDidLoad()

        bckgImageView.frame = self.view.frame
        self.view.addSubview(bckgImageView)

        animateBackground()

    }

    func animateBackground() {

        UIView.transition(with: self.view,
                          duration: 5,
                          options: .transitionCrossDissolve,
                          animations: { self.bckgImageView.image = UIImage(named: "two") },
                          completion: nil)

    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        bckgImageView.frame = self.view.frame
    }

}

Answer 2

首先，您要将图像视图的框架设置为 "root" 视图的框架，即在 viewDidLoad() 中定义的 not-yet。你最好使用约束并让 auto-layout 调整视图的大小。

其次，如果您在 viewDidLoad() 甚至 viewDidLayoutSubviews() 开始动画，屏幕还不可见 --- 所以您看不到初始图像（或者您只看到如果动画很短，请看得很简单。

所以，在 viewDidAppear() 开始你的动画，或者稍微延迟一下，如下所示：

class ViewController: UIViewController {

    var bckgImageView = UIImageView(image: UIImage(named: "one"))

    override func viewDidLoad() {
        super.viewDidLoad()

        self.view.addSubview(bckgImageView)
        bckgImageView.translatesAutoresizingMaskIntoConstraints = false

        // constrain image view to all 4 sides
        NSLayoutConstraint.activate([
            bckgImageView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            bckgImageView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
            bckgImageView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            bckgImageView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
            ])

    }

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

        // start animation after 1 second
        DispatchQueue.main.asyncAfter(deadline: .now() + 1.0, execute: {
            self.animateBackground()
            })

    }

    func animateBackground() {

        UIView.transition(with: self.view,
                          duration: 5,
                          options: .transitionCrossDissolve,
                          animations: { self.bckgImageView.image = UIImage(named: "two") },
                          completion: nil)

    }
}

尝试在 UIImageView 中的图像之间淡入淡出时出现白屏

White screen when attempting to fade between images in UIImageView

image

uiimageview

uiviewanimation

ios

swift