SwiftUI - 滑动文本动画和定位

Question

在我进一步了解 SwiftUI 的过程中，我仍然对将我的元素定位在ZStack.

目标是“简单”，我想要一个文本，如果文本太长，它会在定义的区域内滑动。假设我有一个 50px 的区域，文本需要 100。我希望文本从右向左滑动，然后从左向右滑动。

目前，我的代码如下所示：

struct ContentView: View {
    @State private var animateSliding: Bool = false
    private let timer = Timer.publish(every: 1, on: .current, in: .common).autoconnect()
    private let slideDuration: Double = 3
    private let text: String = "Hello, World! My name is Oleg and I would like this text to slide!"

    var body: some View {
        GeometryReader(content: { geometry in
            VStack(content: {
                Text("Hello, World! My name is Oleg!")
                    .font(.system(size: 20))
                    .id("SlidingText-Animation")
                    .alignmentGuide(VerticalAlignment.center, computeValue: { $0[VerticalAlignment.center] })
                    .position(y: geometry.size.height / 2 + self.textSize(fromWidth: geometry.size.width).height / 2)
                    .fixedSize()
                    .background(Color.red)
                    .animation(Animation.easeInOut(duration: 2).repeatForever())
                    .position(x: self.animateSliding ? -self.textSize(fromWidth: geometry.size.width).width : self.textSize(fromWidth: geometry.size.width).width)
                    .onAppear(perform: {
                        self.animateSliding.toggle()
                    })
            })
                .background(Color.yellow)
                .clipShape(Rectangle())
        })
            .frame(width: 200, height: 80)
    }

    func textSize(fromWidth width: CGFloat, fontName: String = "System Font", fontSize: CGFloat = UIFont.systemFontSize) -> CGSize {
        let text: UILabel = .init()
        text.text = self.text
        text.numberOfLines = 0
        text.font = UIFont.systemFont(ofSize: 20) // (name: fontName, size: fontSize)
        text.lineBreakMode = .byWordWrapping
        return text.sizeThatFits(CGSize.init(width: width, height: .infinity))
    }
}

您是否有任何建议如何将文本垂直居中在其父级中并执行从好的位置开始的动画？

感谢您未来的任何帮助，非常感谢！

编辑：

我重组了我的代码，并改变了我正在做的一些事情。

struct SlidingText: View {
    let geometryProxy: GeometryProxy

    @State private var animateSliding: Bool = false
    private let timer = Timer.publish(every: 1, on: .current, in: .common).autoconnect()
    private let slideDuration: Double = 3
    private let text: String = "Hello, World! My name is Oleg and I would like this text to slide!"

    var body: some View {
        ZStack(alignment: .leading, content: {
            Text(text)
                .font(.system(size: 20))
//                .lineLimit(1)
                .id("SlidingText-Animation")
                .fixedSize(horizontal: true, vertical: false)
                .background(Color.red)
                .animation(Animation.easeInOut(duration: slideDuration).repeatForever())
                .offset(x: self.animateSliding ? -textSize().width : textSize().width)
                .onAppear(perform: {
                    self.animateSliding.toggle()
                })
        })
            .frame(width: self.geometryProxy.size.width, height: self.geometryProxy.size.height)
            .clipShape(Rectangle())
            .background(Color.yellow)
    }

    func textSize(fontName: String = "System Font", fontSize: CGFloat = 20) -> CGSize {
        let text: UILabel = .init()
        text.text = self.text
        text.numberOfLines = 0
        text.font = UIFont(name: fontName, size: fontSize)
        text.lineBreakMode = .byWordWrapping
        let textSize = text.sizeThatFits(CGSize(width: self.geometryProxy.size.width, height: .infinity))
        print(textSize.width)
        return textSize
    }
}

struct ContentView: View {
    var body: some View {
        GeometryReader(content: { geometry in
            SlidingText(geometryProxy: geometry)
        })
            .frame(width: 200, height: 40)

    }
}

现在动画看起来很不错，除了我在左右两边都有填充，我不明白为什么。

Edit2：我还注意到通过更改text.font = UIFont.systemFont(ofSize: 20)bytext.font = UIFont.systemFont(ofSize: 15)使文本正确适合。我不明白系统字体与SwiftUI或之间是否存在差异UIKit。它不应该..

在我的情况下使用解决方案进行最终编辑：

struct SlidingText: View {
    let geometryProxy: GeometryProxy
    @Binding var text: String
    @Binding var fontSize: CGFloat

    @State private var animateSliding: Bool = false
    private let timer = Timer.publish(every: 5, on: .current, in: .common).autoconnect()
    private let slideDuration: Double = 3

    var body: some View {
            ZStack(alignment: .leading, content: {
                VStack {
                    Text(text)
                        .font(.system(size: self.fontSize))
                        .background(Color.red)
                }
                .fixedSize()
                .frame(width: geometryProxy.size.width, alignment: animateSliding ? .trailing : .leading)
                .clipped()
                .animation(Animation.linear(duration: slideDuration))
                .onReceive(timer) { _ in
                    self.animateSliding.toggle()
                }
            })
                .frame(width: self.geometryProxy.size.width, height: self.geometryProxy.size.height)
                .clipShape(Rectangle())
                .background(Color.yellow)
    }
}

struct ContentView: View {
    @State var text: String = "Hello, World! My name is Oleg and I would like this text to slide!"
    @State var fontSize: CGFloat = 20

    var body: some View {
        GeometryReader(content: { geometry in
            SlidingText(geometryProxy: geometry, text: self.$text, fontSize: self.$fontSize)
        })
            .frame(width: 400, height: 40)
        .padding(0)

    }
}

这是视觉上的结果。

Answer 1

这是一个可能的简单方法 - 这个想法就像改变容器中的文本对齐一样简单，其他任何东西都可以像往常一样调整。

使用 Xcode 12 / iOS 14 准备和测试的演示

struct DemoSlideText: View {
    let text = "Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor"

    @State private var go = false
    var body: some View {
        VStack {
            Text(text)
        }
        .fixedSize()
        .frame(width: 300, alignment: go ? .trailing : .leading)
        .clipped()
        .onAppear { self.go.toggle() }
        .animation(Animation.linear(duration: 5).repeatForever(autoreverses: true))
    }
}