ios - 在 View 上动画 UIIMageView Alpha 确实加载

Question

我正在尝试为我的 HomeController 制作背景图像。

我想淡入图像，因此我希望为它的 alpha 属性设置动画。

我在这里找到了很多关于这个问题的答案，但是很多看起来已经过时(obj c、iOS 3/4/5 等)并且按照推荐的方法，我仍然无法让这个动画工作。

谁能告诉我我的代码有什么问题吗？

我想为 backgroundImage 制作动画。我已将动画代码放在 setupView 方法的末尾。

它并没有像我希望的那样“淡入”，基本上 alpha 直接跳到 0.7

import UIKit

class HomeController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        setupView()
    }

    private let backgroundImage: UIImageView = {
        let image = UIImageView()
        image.image = #imageLiteral(resourceName: "foggy").withRenderingMode(.alwaysOriginal)
        image.contentMode = .scaleToFill
       image.alpha = 0
        image.isOpaque = false

        return image
    }()

    private let currentLocation: UIButton = {
        let button = UIButton(type: .system)
        button.setTitle("Southampton, UK", for: .normal)
        button.titleLabel?.font = UIFont.systemFont(ofSize: 24)
        button.contentMode = .center
        button.setTitleColor(.black, for: .normal)
        button.addTarget(self, action: #selector(onPressLocation), for: .touchUpInside)

        return button
    }()

    private let currentTemp: UIButton = {
        let button = UIButton(type: .system)
        button.setTitle("37°C", for: .normal)
        button.titleLabel?.font = UIFont.systemFont(ofSize: 54, weight: .thin)
        button.contentMode = .center
        button.setTitleColor(.white, for: .normal)
        button.addTarget(self, action: #selector(onPressTemp), for: .touchUpInside)

        return button
    }()

}

extension HomeController {

    @objc fileprivate func onPressLocation() -> Void {
        print("Location pressed.")
    }

    @objc fileprivate func onPressTemp() -> Void {
        self.currentTemp.setTitle("98°F", for: .normal)
    }

    fileprivate func setupView() -> Void {

        view.backgroundColor = .white

        // MARK: Background Image
        view.addSubview(backgroundImage)
        backgroundImage.anchor(
            top: view.safeAreaLayoutGuide.topAnchor,
            left: view.safeAreaLayoutGuide.leftAnchor,
            bottom: view.safeAreaLayoutGuide.bottomAnchor,
            right: view.safeAreaLayoutGuide.rightAnchor,
            paddingTop: 0,
            paddingLeft: 0,
            paddingBottom: 0,
            paddingRight: 0,
            width: 0,
            height: 0
        )

        // MARK: Current Location
        view.addSubview(currentLocation)
        currentLocation.anchor(
            top: view.safeAreaLayoutGuide.topAnchor,
            left: view.safeAreaLayoutGuide.leftAnchor,
            right: view.safeAreaLayoutGuide.rightAnchor,
            paddingTop: 50,
            paddingLeft: 0,
            paddingBottom: 0,
            paddingRight: 0,
            width: 0,
            height: 26,
            centerX: view.centerXAnchor
        )

        // MARK: Temp Button
        view.addSubview(currentTemp)
        currentTemp.anchor(
            top: currentLocation.bottomAnchor,
            paddingTop: 10,
            paddingLeft: 0,
            paddingBottom: 0,
            paddingRight: 0,
            width: 200,
            height: 70,
            centerX: view.centerXAnchor
        )

        // MARK: Animations
        UIView.animate(withDuration: 6, delay: 3, options: .curveEaseInOut, animations: {
            self.backgroundImage.alpha = 0.7
        }, completion: nil)

    }
}

Answer 1

当调用 viewDidLoad 时，

IBOutlets 不可见，因此请调用 viewDidAppear 中的 setupView 方法在您的 View 出现在屏幕上之后。

希望这对您有所帮助。