SwiftUI: Animate Text color - foregroundColor()

Question

I've been trying to work on animating various parts of the UI, but it seems as though you can't animate a SwiftUI Text's foregroundColor? I want to switch the color of some text smoothly when a state changes. This works fine if I animate the background color of the Text's surrounding view, but foreground color does not work. Has anyone had any luck animating a change like this? Unsure if this is an Xcode beta bug or it's intended functionality...

Text(highlightedText)
    .foregroundColor(color.wrappedValue)
    .animation(.easeInOut)

// Error: Cannot convert value of type 'Text' to closure result type '_'

Answer 1

有一个更简单的方法，借用 Apple 的“Animating Views and Transitions”教程代码。HikeGraph 中 GraphCapsule 的实例化证明了这一点。

虽然foregroundColor不能动画，但colorMultiply可以。将前景色设置为白色并使用 colorMultiply 设置您想要的实际颜色。从红色到蓝色的动画：

struct AnimateDemo: View {
    @State private var color = Color.red

    var body: some View {
        Text("Animate Me!")
            .foregroundColor(Color.white)
            .colorMultiply(self.color)
            .onTapGesture {
                withAnimation(.easeInOut(duration: 1)) {
                    self.color = Color.blue
                }
        }
    }
}

struct AnimateDemo_Previews: PreviewProvider {
    static var previews: some View {
        AnimateDemo()
    }
}

Answer 2

的颜色属性在或Text中不可设置动画。但你可以像这样实现你需要的结果：SwiftUIUIKit

struct ContentView: View {

    @State var highlighted = false

    var body: some View {
        VStack {
            ZStack {
            // Highlighted State
            Text("Text To Change Color")
                .foregroundColor(.red)
                .opacity(highlighted ? 1 : 0)

            // Normal State
            Text("Text To Change Color")
                .foregroundColor(.blue)
                .opacity(highlighted ? 0 : 1)
            }
            Button("Change") {
                withAnimation(.easeIn) {
                    self.highlighted.toggle()
                }
            }
        }
    }
}

您可以将此功能封装在自定义中View并在您喜欢的任何地方使用它。

Answer 3

SwiftUI 中有一个很好的协议，可以让你为任何东西设置动画。即使是不可动画的东西！（如文本颜色）。该协议称为 AnimatableModifier。

如果你想了解更多，我写了一篇完整的文章来解释它是如何工作的：https : //swiftui-lab.com/swiftui-animations-part3/

下面是一个关于如何完成这样一个视图的例子：

AnimatableColorText(from: UIColor.systemRed, to: UIColor.systemGreen, pct: flag ? 1 : 0) {
    Text("Hello World").font(.largeTitle)
}.onTapGesture {
    withAnimation(.easeInOut(duration: 2.0)) {
      self.flag.toggle()
    }
}

和实施：

struct AnimatableColorText: View {
    let from: UIColor
    let to: UIColor
    let pct: CGFloat
    let text: () -> Text

    var body: some View {
        let textView = text()

        // This should be enough, but there is a bug, so we implement a workaround
        // AnimatableColorTextModifier(from: from, to: to, pct: pct, text: textView)

        // This is the workaround
        return textView.foregroundColor(Color.clear)
            .overlay(Color.clear.modifier(AnimatableColorTextModifier(from: from, to: to, pct: pct, text: textView)))
    }

    struct AnimatableColorTextModifier: AnimatableModifier {
        let from: UIColor
        let to: UIColor
        var pct: CGFloat
        let text: Text

        var animatableData: CGFloat {
            get { pct }
            set { pct = newValue }
        }

        func body(content: Content) -> some View {
            return text.foregroundColor(colorMixer(c1: from, c2: to, pct: pct))
        }

        // This is a very basic implementation of a color interpolation
        // between two values.
        func colorMixer(c1: UIColor, c2: UIColor, pct: CGFloat) -> Color {
            guard let cc1 = c1.cgColor.components else { return Color(c1) }
            guard let cc2 = c2.cgColor.components else { return Color(c1) }

            let r = (cc1[0] + (cc2[0] - cc1[0]) * pct)
            let g = (cc1[1] + (cc2[1] - cc1[1]) * pct)
            let b = (cc1[2] + (cc2[2] - cc1[2]) * pct)

            return Color(red: Double(r), green: Double(g), blue: Double(b))
        }

    }
}