[Rainbow ViewModifier] Rainbow animation view modifiers for SwiftUI #SwiftUI #ViewModifier

Rainbow.md

Rainbow.swift

//
//  Rainbow.swift
//  Created by Kieran Brown on 4/15/20.


import SwiftUI

struct Rainbow: ViewModifier {
    let hueColors = stride(from: 0, to: 1, by: 0.1).map {
        Color(hue: $0, saturation: 1, brightness: 1)
    }
    
    func body(content: Content) -> some View {
        content
            .overlay(GeometryReader { (proxy: GeometryProxy) in
                ZStack {
                    LinearGradient(gradient: Gradient(colors: self.hueColors),
                                   startPoint: .leading,
                                   endPoint: .trailing)
                        .frame(width: proxy.size.width, height: proxy.size.height)
                }
            })
            .mask(content)
    }
}
extension View {
    func rainbow() -> some View {
        self.modifier(Rainbow())
    }
}

struct RainbowAnimation: ViewModifier {
    // 1
    @State var isOn: Bool = false
    let hueColors = stride(from: 0, to: 1, by: 0.01).map {
        Color(hue: $0, saturation: 1, brightness: 1)
    }
    // 2
    var duration: Double = 4
    var animation: Animation {
        Animation
            .linear(duration: duration)
            .repeatForever(autoreverses: false)
    }
    
    func body(content: Content) -> some View {
    // 3
        let gradient = LinearGradient(gradient: Gradient(colors: hueColors+hueColors), startPoint: .leading, endPoint: .trailing)
        return content.overlay(GeometryReader { proxy in
            ZStack {
                gradient
                    // 4
                    .frame(width: 2*proxy.size.width)
                    // 5
                    .offset(x: self.isOn ? -proxy.size.width/2 : proxy.size.width/2)
            }
        })
            // 6
            .onAppear {
                withAnimation(self.animation) {
                    self.isOn = true
                }
        }
        .mask(content)
    }
}

extension View {
    func rainbowAnimation() -> some View {
        self.modifier(RainbowAnimation())
    }
}

struct RainbowExamples: View {
    var body: some View {
        ZStack {
            Color(white: 0.1).edgesIgnoringSafeArea(.all)
            VStack {
                Capsule()
                    .frame(width: 200, height: 75)
                    .rainbow()
                
                RoundedRectangle(cornerRadius: 10)
                    .inset(by: 5)
                    .stroke(Color.black, lineWidth: 5)
                    .frame(width: 300, height: 100)
                    .rainbowAnimation()
                
                Text("Rainbow")
                    .font(.system(size: 100))
                    .rainbowAnimation()
            }
        }
    }
}

struct Rainbow_Previews: PreviewProvider {
    static var previews: some View {
        RainbowExamples()
    }
}

Thanks, really useful. I a trying to edit it so it doesn't display the original text color at the begining. I am running it on X Code12 and simulators and the text is black then the animation comes from the rigth

Got it, just changed this line 👍

.offset(x: self.isOn ? -proxy.size.width/2 : proxy.size.width/2)
to
.offset(x: self.isOn ? -proxy.size.width/2 : 0)

And if you change it to :

.offset(x: self.isOn ? -proxy.size.width : 0)

it looks much nicer the animation is flowing normally and the colors don't come back at the middle.

I'm running this on XCode 13.1 and found some issues when attaching the .rainbow() modifier to a view nested inside of a NavigationView. The modified view slides in from the top left corner along with displaying the rainbow effect. To fix this I changed the following bit of code:

        .onAppear {
            withAnimation(self.animation) {
                self.isOn = true
            }
        }

To the following:

        .onAppear {
            DispatchQueue.main.async {
                withAnimation(self.animation) {
                    self.isOn = true
                }
            }
        }

Not sure why extra animation is added to the parent view but wrapping withAnimation with async seems to fix the issue.