How can I access the subviews in SwiftUI?

Question

I am trying our SwiftUI and want to create a component on the lines of SwiftUI's components. So, here is what I am trying to do:

Create a new view extending View

struct CustomComponent: View {
    var title: String
    var body: some View {
        HStack {
            Image(systemName: "") // This would be updated through style
            Text(verbatim: title)
        }

    }
}

extension View {

    public func componentStyle<S>(_ style: S) -> some View where S : ComponentStyle {
        guard self is CustomComponent else {
            return AnyView(self)
        }

        return AnyView(
// Here I want to add the spacing attribute of the style to the HStack.
// Also I want to update the Image with the corresponding style's icon.
// If it's not possible here, please suggest alternate place.
            self
                .foregroundColor(style.tintColor)
                .frame(height: style.height)
        )
    }

}

public protocol ComponentStyle {
    var icon: String { get }
    var tintColor: Color { get }
    var spacing: CGFloat { get }
    var height: CGFloat { get }
}

struct ErrorStyle: ComponentStyle {
    var icon: String {
        return "xmark.octagon"
    }

    var tintColor: Color {
        return .red
    }

    var spacing: CGFloat {
        return 8
    }

    var height: CGFloat {
        return 24
    }
}

How can I achieve the following:

• How can I add the spacing attribute of the style to the HStack?
• How can I update the Image with the corresponding style's icon?

Answer 1

You can create a custom EnvironmentKey:

extension EnvironmentValues {
    private struct ComponentStyleKey: EnvironmentKey {
        static let defaultValue: ComponentStyle = ErrorStyle()
    }
    
    var componentStyle: ComponentStyle {
        get { self[ComponentStyleKey] }
        set { self[ComponentStyleKey] = newValue }
    }
}

and use it to pass some ComponentStyle as an @Environment variable:

struct ContentView: View {
    var body: some View {
        CustomComponent(title: "title")
            .componentStyle(ErrorStyle())
    }
}

struct CustomComponent: View {
    @Environment(\.componentStyle) private var style: ComponentStyle
    var title: String

    var body: some View {
        HStack(spacing: style.spacing) {
            Image(systemName: style.icon)
            Text(verbatim: title)
        }
    }
}

extension CustomComponent {
    func componentStyle<S>(_ style: S) -> some View where S: ComponentStyle {
        environment(\.componentStyle, style)
    }
}