ios - 无法在 Swift 中使用时间延迟为 UIImage 设置动画

Question

我试图在 3 秒后为 UIImage 的 alpha 设置动画。默认情况下，alpha 设置为 0，3 秒后，alpha 应更改为 1，从而向用户显示图像。我为动画编写的代码确实将 alpha 设置为 0，但我无法在 3 秒后将 alpha 更改为 1。我是 swift 的新手，不确定我哪里出了问题。这是我的代码。

import UIKit

class WelcomeOneViewController: UIViewController {

@IBOutlet weak var swipeImageView: UIImageView!

override func viewDidLoad() {
    super.viewDidLoad()
    swipeImageView.alpha = 0
}

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

func displaySwipeView() {
    UIView.animate(withDuration: 1.0, delay: 3.0, options: .beginFromCurrentState, animations: {

        DispatchQueue.main.async { [weak self] in
            self?.swipeImageView.alpha = 1
        }

    }, completion: nil)
}

}

Answer 1

用这段代码试试:

import UIKit

class WelcomeOneViewController: UIViewController {

    @IBOutlet weak var swipeImageView: UIImageView!

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        swipeImageView.alpha = 0
    }

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

    func displaySwipeView() {
        swipeImageView.alpha = 0
        UIView.animate(withDuration: 1.0, delay: 3.0, options: [], animations: {
            self.swipeImageView.alpha = 1
        }, completion: nil)
    }

}