A wrapper view that provides a mutable Binding to its content closure. Useful in Xcode Previews for interactive previews of views that take a Binding.

Stateful.swift

import SwiftUI

/// A wrapper view that provides a mutable Binding to its content closure.
///
/// Useful in Xcode Previews for interactive previews of views that take a Binding.
struct Stateful<Value, Content: View>: View {
    var content: (Binding<Value>) -> Content
    @State private var state: Value

    init(initialState: Value, @ViewBuilder content: @escaping (Binding<Value>) -> Content) {
        self._state = State(initialValue: initialState)
        self.content = content
    }

    var body: some View {
        content($state)
    }
}

struct Stateful_Previews: PreviewProvider {
    static var previews: some View {
        VStack {
            Text("Interactive Previews for Bindings!")
                .font(.headline)
            Stateful(initialState: true) { $state in
                Toggle("Toggle", isOn: $state)
            }
            Stateful(initialState: 0.25) { $state in
                HStack {
                    Text("\(state, format: .percent.precision(.fractionLength(0)))")
                        .padding(.trailing, 20)
                    Slider(value: $state, in: 0...1) {
                        Text("Percentage")
                    }
                }
                .font(.body.monospacedDigit())
            }
        }
        .padding()
        .previewLayout(.fixed(width: 300, height: 300))
    }
}