A SwiftUI view modifier for simple preview providers.

PreviewProviderModifier.swift

import SwiftUI

enum PreviewProviderMode: CaseIterable {
    
    /// Use for a light appearance preview.
    case lightMode
    
    /// Use for a dark appearance preview.
    case darkMode
    
    /// Use for a right-to-left layout preview.
    case rightToLeft
    
    /// Use for a preview with a large text size.
    case largeText
    
    /// Use for a redacted placeholder preview.
    case redacted
    
}

fileprivate struct PreviewProviderModifier: ViewModifier {
    
    /// The preview provider modes to display.
    let modes: [PreviewProviderMode]
    
    func body(content: Content) -> some View {
        Group {
            if modes.contains(.lightMode) {
                content
                    .previewDisplayName("Light Mode")
                    .environment(\.colorScheme, .light)
            }
            
            if modes.contains(.darkMode) {
                content
                    .previewDisplayName("Dark Mode")
                    .environment(\.colorScheme, .dark)
            }
            
            if modes.contains(.rightToLeft) {
                content
                    .previewDisplayName("Right To Left")
                    .environment(\.layoutDirection, .rightToLeft)
            }
            
            if modes.contains(.largeText) {
                content
                    .previewDisplayName("Large Text")
                    .environment(\.dynamicTypeSize, .accessibility5)
            }
            
            if modes.contains(.redacted) {
                content
                    .previewDisplayName("Redacted")
                    .redacted(reason: .placeholder)
            }
        }
    }
    
}

extension View {
    
    /// Creates a group of views with various environment settings that are useful for previews.
    ///
    /// - Parameters:
    ///   - modes: The preview provider modes to display, such as light mode, dark mode, right-to-left layout, and large text.
    func makeForPreviewProvider(_ modes: [PreviewProviderMode] = PreviewProviderMode.allCases) -> some View {
        modifier(PreviewProviderModifier(modes: modes))
    }
    
    /// Creates a group of views with various environment settings that are useful for previews.
    ///
    /// - Parameters:
    ///   - mode: The preview provider mode to display, such as light mode, dark mode, right-to-left layout, or large text.
    func makeForPreviewProvider(_ mode: PreviewProviderMode) -> some View {
        modifier(PreviewProviderModifier(modes: [mode]))
    }
    
    /// Creates a group of views with various environment settings that are useful for previews.
    ///
    /// - Parameters:
    ///   - modes: The preview provider modes to be excluded from being displayed. All other modes will be displayed.
    func makeForPreviewProvider(excluding modes: [PreviewProviderMode]) -> some View {
        let included = PreviewProviderMode.allCases.filter { modes.contains($0) == false }
        return modifier(PreviewProviderModifier(modes: included))
    }
    
    /// Creates a group of views with various environment settings that are useful for previews.
    ///
    /// - Parameters:
    ///   - mode: The preview provider mode to be excluded from being displayed. All other modes will be displayed.
    func makeForPreviewProvider(excluding mode: PreviewProviderMode) -> some View {
        makeForPreviewProvider(excluding: [mode])
    }
    
}