Source code for CodeSlicing episode on advanced activity indicators - modifier extraction

CircularActivityIndicatorAdvancedDemo.swift

//
//  CircularActivityIndicatorAdvancedDemo.swift
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
//  of the Software, and to permit persons to whom the Software is furnished to do so,
//  subject to the following conditions:
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
//  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
//  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
//  COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
//  AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
//  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//  Copyright © 2021 Adam Fordyce. All rights reserved.
//

import PureSwiftUI

struct CircularActivityIndicatorAdvancedDemo: View {

    var body: some View {
        GeometryReader { (geo: GeometryProxy) in
            Capsule()
                .fillColor(.black)
                .frame(geo.sizeScaled(0.15, 0.3))
                .greedyFrame()
                .renderAsActivityIndicator(numSegments: 8, offset: geo.heightScaled(0.35), duration: 1, fadeFactor: 0.8, maintainOrientation: false)
        }
    }
}

private struct ActivityIndicatorModifier: ViewModifier {
    
    private let numSegments: Int
    private let offset: CGFloat
    private let duration: Double
    private let fadeFactor: Double
    private let maintainOrientation: Bool
    
    private let rotationPerSegment: Angle
    private let delayPerSegment: Double
    
    @State private var animating = false
    
    init(numSegments: Int, offset: CGFloat, duration: Double, fadeFactor: Double = 1, maintainOrientation: Bool = false) {
        self.numSegments = numSegments
        self.offset = offset
        self.duration = duration
        self.fadeFactor = fadeFactor
        self.maintainOrientation = maintainOrientation
        let fractionPerSegment = 1 / numSegments.asDouble
        self.rotationPerSegment = .cycles(fractionPerSegment)
        self.delayPerSegment = duration * fractionPerSegment
    }
    
    func body(content: Content) -> some View {
        ZStack {
            ForEach(0..<numSegments) { index in
                let rotation = rotationPerSegment * index
                let delay = delayPerSegment * index.asDouble
                content
                    .rotateIf(maintainOrientation, -rotation)
                    .yOffset(-offset)
                    .rotate(rotation)
                    .opacityIfNot(animating, 0)
                    .animation(Animation.linear(duration: 0.001).delay(delay))
                    .modifier(OpacityFadingModifier(fadeFactor: fadeFactor, animating: animating))
                    .animation(Animation.linear(duration: duration).repeatForever(autoreverses: false).delay(delay))
            }
        }
        .onAppear {
            animating = true
        }
    }
}

private extension View {
    
    func renderAsActivityIndicator(numSegments: Int, offset: CGFloat, duration: Double, fadeFactor: Double = 1, maintainOrientation: Bool = false) -> some View {
        modifier(ActivityIndicatorModifier(numSegments: numSegments, offset: offset, duration: duration, fadeFactor: fadeFactor, maintainOrientation: maintainOrientation))
    }
}

private struct OpacityFadingModifier: AnimatableModifier {
    
    private let fadeFactor: Double
    
    var animatableData: Double
    
    init(fadeFactor: Double = 1, animating: Bool) {
        self.fadeFactor = fadeFactor
        animatableData = animating ? 1 : 0
    }
    
    private var animatedOpacity: Double {
        (fadeFactor - animatableData) / fadeFactor
    }
    
    func body(content: Content) -> some View {
        content
            .opacity(animatedOpacity)
            .animation(nil)
    }
}

struct CircularActivityIndicatorAdvancedDemo_Previews: PreviewProvider {
    struct CircularActivityIndicatorAdvancedDemo_Harness: View {

        var body: some View {
            CircularActivityIndicatorAdvancedDemo()
                .frame(300)
        }
    }

    static var previews: some View {
        CircularActivityIndicatorAdvancedDemo_Harness()
            .previewDevice(.iPhone_12_Pro_Max)
    }
}