Customizing ProgressView with ProgressViewStyle

Updated for Xcode 14.1

SwiftUI gives us the ProgressViewStyle protocol to create custom designs for ProgressView, allowing us to read how complete the progress view and take that into account in our design.

To make a custom ProgressView style, you need to create a struct that has a makeBody() method accepting the current configuration of the view. You can then go ahead and render the progress however you want – perhaps a text percentage, perhaps a growing circle, and so on – then return your finished layout to be rendered.

To demonstrate this, here’s a custom style that creates a gauge, showing progress as a stroked circle that completes as progress ramps up:

struct GaugeProgressStyle: ProgressViewStyle {
    var strokeColor = Color.blue
    var strokeWidth = 25.0

    func makeBody(configuration: Configuration) -> some View {
        let fractionCompleted = configuration.fractionCompleted ?? 0

        return ZStack {
            Circle()
                .trim(from: 0, to: fractionCompleted)
                .stroke(strokeColor, style: StrokeStyle(lineWidth: strokeWidth, lineCap: .round))
                .rotationEffect(.degrees(-90))
        }
    }
}

// A view letting you adjust the progress with tap gestures
struct ContentView: View {
    @State private var progress = 0.2

    var body: some View {
        ProgressView(value: progress, total: 1.0)
            .progressViewStyle(GaugeProgressStyle())
            .frame(width: 200, height: 200)
            .contentShape(Rectangle())
            .onTapGesture {
                if progress < 1.0 {
                    withAnimation {
                        progress += 0.2
                    }
                }
            }
    }
}

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