Animating Text in Swift UI - ios

Question

How would it be possible to animate Text or TextField views from Swift UI?
By animation I mean, that when the text changes it will "count up".
For example given some label, how can an animation be created that when I set the labels text to "100" it goes up from 0 to 100. I know this was possible in UIKit using layers and CAAnimations, but using the .animation() function in Swift UI and changing the text of a Text or TextField does not seem to do anything in terms of animation.
I've taken a look at Animatable protocol and its related animatableData property but it doesn't seem like Text nor TextField conform to this. I'm trying to create a label that counts up, so given some value, say a Double the changes to that value would be tracked, either using #State or #Binding and then the Text or TextField would animate its content (the actual string text) from what the value was at to what it was set to.
Edit:
To make it clearer, I'd like to recreate a label that looks like this when animated:

Answer 1

There is a pure way of animating text in SwiftUI. Here's an implementation of your progress indicator using the AnimatableModifier protocol in SwiftUI:
I've written an extensive article documenting the use of AnimatableModifier (and its bugs). It includes the progress indicator too. You can read it here: https://swiftui-lab.com/swiftui-animations-part3/
struct ContentView: View {
#State private var percent: CGFloat = 0
var body: some View {
VStack {
Spacer()
Color.clear.overlay(Indicator(pct: self.percent))
Spacer()
HStack(spacing: 10) {
MyButton(label: "0%", font: .headline) { withAnimation(.easeInOut(duration: 1.0)) { self.percent = 0 } }
MyButton(label: "27%", font: .headline) { withAnimation(.easeInOut(duration: 1.0)) { self.percent = 0.27 } }
MyButton(label: "100%", font: .headline) { withAnimation(.easeInOut(duration: 1.0)) { self.percent = 1.0 } }
}
}.navigationBarTitle("Example 10")
}
}
struct Indicator: View {
var pct: CGFloat
var body: some View {
return Circle()
.fill(LinearGradient(gradient: Gradient(colors: [.blue, .purple]), startPoint: .topLeading, endPoint: .bottomTrailing))
.frame(width: 150, height: 150)
.modifier(PercentageIndicator(pct: self.pct))
}
}
struct PercentageIndicator: AnimatableModifier {
var pct: CGFloat = 0
var animatableData: CGFloat {
get { pct }
set { pct = newValue }
}
func body(content: Content) -> some View {
content
.overlay(ArcShape(pct: pct).foregroundColor(.red))
.overlay(LabelView(pct: pct))
}
struct ArcShape: Shape {
let pct: CGFloat
func path(in rect: CGRect) -> Path {
var p = Path()
p.addArc(center: CGPoint(x: rect.width / 2.0, y:rect.height / 2.0),
radius: rect.height / 2.0 + 5.0,
startAngle: .degrees(0),
endAngle: .degrees(360.0 * Double(pct)), clockwise: false)
return p.strokedPath(.init(lineWidth: 10, dash: [6, 3], dashPhase: 10))
}
}
struct LabelView: View {
let pct: CGFloat
var body: some View {
Text("\(Int(pct * 100)) %")
.font(.largeTitle)
.fontWeight(.bold)
.foregroundColor(.white)
}
}
}

Answer 2

You can use a CADisplayLink in a BindableObject to create a timer that updates your text during the animation. Gist
class CADisplayLinkBinding: NSObject, BindableObject {
let didChange = PassthroughSubject<CADisplayLinkBinding, Never>()
private(set) var progress: Double = 0.0
private(set) var startTime: CFTimeInterval = 0.0
private(set) var duration: CFTimeInterval = 0.0
private(set) lazy var displayLink: CADisplayLink = {
let link = CADisplayLink(target: self, selector: #selector(tick))
link.add(to: .main, forMode: .common)
link.isPaused = true
return link
}()
func run(for duration: CFTimeInterval) {
let now = CACurrentMediaTime()
self.progress = 0.0
self.startTime = now
self.duration = duration
self.displayLink.isPaused = false
}
#objc private func tick() {
let elapsed = CACurrentMediaTime() - self.startTime
self.progress = min(1.0, elapsed / self.duration)
self.displayLink.isPaused = self.progress >= 1.0
self.didChange.send(self)
}
deinit {
self.displayLink.invalidate()
}
}
And then to use it:
#ObjectBinding var displayLink = CADisplayLinkBinding()
var body: some View {
Text("\(Int(self.displayLink.progress*100))")
.onAppear {
self.displayLink.run(for: 10.0)
}
}