如何在添加为子视图时设置交叉融合视图的动画？

Question

我正在当前视图底部的UIViewController中添加一个视图作为子视图。我可以使用alpha制作淡入淡出动画，但我想将其显示为类似键盘弹出窗口的幻灯片。

let popup: UIView = ..
popup.alpha = 0.0
self.view.addSubView(popup)
UIView.animate(withDuration: 0.3, animations: {
    popup.alpha = 1.0
}) { _ in
}

如何设置动画？

Answer 1

要通过仅添加子视图来实现交叉淡入淡出，请尝试UIView.transition（with：持续时间：选项：动画：完成：）在动画块期间添加您的视图。

快速操场：

//: A UIKit based Playground for presenting user interface

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let label = UILabel()
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
        label.text = "Hello World!"
        label.textColor = .black

        view.addSubview(label)
        self.view = view
    }

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

        let orangeView = UIView(frame: CGRect(origin: CGPoint(x: view.bounds.midX, y: view.bounds.midY), size: CGSize(width: 100, height: 100)))

        orangeView.backgroundColor = .orange
        DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(300)) {
            UIView.transition(with: self.view, duration: 0.6, options: .transitionCrossDissolve, animations: {
                self.view.addSubview(orangeView)
            }) { _ in

            }

        }
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

Answer 2

您可以更新帧，但我喜欢使用变换来设置动画，这样您仍然可以使用约束，而不必处理约束。

let popup: UIView = ..
popup.transform = CGAffineTransform(translationX: 0, y: popup.bounds.height)
self.view.addSubView(popup)
UIView.animate(withDuration: 0.3, animations: {
    popup.transform = .identity
}) { _ in
}

假设视图位于屏幕底部，则将视图向下平移等于其高度的量，然后将变换设置回其标识（即原始位置）的动画。