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Customizing ProgressView with ProgressViewStyle

Paul Hudson    @twostraws   

Updated for Xcode 12.5

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: CGFloat(fractionCompleted))
                .stroke(strokeColor, style: StrokeStyle(lineWidth: CGFloat(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)
            .onTapGesture {
                if progress < 1.0 {
                    withAnimation {
                        progress += 0.2
                    }
                }
            }
    }
}

Notice how my custom style rotates the circle anti-clockwise by 90 degrees, so the circle draws it progress from the top.

Customizing Toggle with ToggleStyle

SwiftUI gives us the ToggleStyle protocol to customize the way Toggle switches look and work. Any struct that conforms to this protocol must implement a makeBody() method that renders the Toggle however you want it, and you’re giving both the label used for the toggle and an isOn binding that you can flip to adjust the toggle.

Important: When you customize a Toggle switch like this, it’s down to you to flip the on state yourself somehow – SwiftUI will not do it for you.

To demonstrate custom Toggle styles, here’s one that uses a button to flip the on state, then adds a custom label to show that state. Rather than use a moving circle like the standard iOS Toggle, I’ve made this show one of two SF Symbols:

struct CheckToggleStyle: ToggleStyle {
    func makeBody(configuration: Configuration) -> some View {
        Button {
            configuration.isOn.toggle()
        } label: {
            Label {
                configuration.label
            } icon: {
                Image(systemName: configuration.isOn ? "checkmark.circle.fill" : "circle")
                    .foregroundColor(configuration.isOn ? .accentColor : .secondary)
                    .accessibility(label: Text(configuration.isOn ? "Checked" : "Unchecked"))
                    .imageScale(.large)
            }
        }
        .buttonStyle(PlainButtonStyle())
    }
}

// An example view showing the style in action
struct ContentView: View {
    @State private var isOn = false

    var body: some View {
        Toggle("Switch Me", isOn: $isOn)
            .toggleStyle(CheckToggleStyle())
    }
}
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