SwiftUI

You are a SwiftUI expert. Apply these patterns when building views and components.

Component Design Principles

Single Responsibility

Each component should do one thing well. Split complex views into smaller, focused components.

Configurable via Initializer

Expose configuration through init parameters, not environment or external state.

Preview-Friendly

Components should be easily previewable in isolation with sensible defaults.

Trailing Closure Style

Always prefer trailing closure syntax for better readability and consistency:

// Preferred: trailing closures
Button {
    saveDocument()
} label: {
    Label("Save", systemImage: "square.and.arrow.down")
}

Section {
    TextField("Name", text: $name)
    TextField("Email", text: $email)
} header: {
    Text("Contact Info")
} footer: {
    Text("We'll never share your email")
}

NavigationLink {
    DetailView(item: item)
} label: {
    ItemRow(item: item)
}

// Avoid: inline style
Button("Save") { saveDocument() }
Section("Header") { content }
NavigationLink("Details", destination: DetailView())

View Composition

Container Components

struct Card<Content: View>: View {
    let content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    var body: some View {
        content
            .padding()
            .background(.background.secondary)
            .clipShape(RoundedRectangle(cornerRadius: 12))
            .shadow(color: .black.opacity(0.1), radius: 4, y: 2)
    }
}

// Usage
Card {
    VStack {
        Text("Title")
        Text("Subtitle")
    }
}

Slot-Based Components

struct ListRow<Leading: View, Trailing: View>: View {
    let title: String
    let leading: Leading
    let trailing: Trailing

    init(
        title: String,
        @ViewBuilder leading: () -> Leading = { EmptyView() },
        @ViewBuilder trailing: () -> Trailing = { EmptyView() }
    ) {
        self.title = title
        self.leading = leading()
        self.trailing = trailing()
    }

    var body: some View {
        HStack {
            leading
            Text(title)
            Spacer()
            trailing
        }
    }
}

// Usage
ListRow(title: "Settings") {
    Image(systemName: "gear")
} trailing: {
    Image(systemName: "chevron.right")
}

Common Patterns

Loading States

struct AsyncContent<Content: View, Placeholder: View>: View {
    let isLoading: Bool
    let content: Content
    let placeholder: Placeholder

    init(
        isLoading: Bool,
        @ViewBuilder content: () -> Content,
        @ViewBuilder placeholder: () -> Placeholder = { ProgressView() }
    ) {
        self.isLoading = isLoading
        self.content = content()
        self.placeholder = placeholder()
    }

    var body: some View {
        if isLoading {
            placeholder
        } else {
            content
        }
    }
}

Empty States

struct EmptyState: View {
    let icon: String
    let title: String
    let message: String
    var action: (() -> Void)?
    var actionTitle: String?

    var body: some View {
        ContentUnavailableView {
            Label(title, systemImage: icon)
        } description: {
            Text(message)
        } actions: {
            if let action, let actionTitle {
                Button(actionTitle, action: action)
                    .buttonStyle(.borderedProminent)
            }
        }
    }
}

// Usage
EmptyState(
    icon: "doc.text",
    title: "No Documents",
    message: "Create your first document to get started",
    action: { createDocument() },
    actionTitle: "Create Document"
)

Error States

struct ErrorView: View {
    let error: Error
    let retry: (() -> Void)?

    var body: some View {
        ContentUnavailableView {
            Label("Something went wrong", systemImage: "exclamationmark.triangle")
        } description: {
            Text(error.localizedDescription)
        } actions: {
            if let retry {
                Button("Try Again", action: retry)
                    .buttonStyle(.bordered)
            }
        }
    }
}

Form Components

Validated Text Field

struct ValidatedField: View {
    let title: String
    @Binding var text: String
    let validation: (String) -> String?

    @State private var error: String?
    @FocusState private var isFocused: Bool

    var body: some View {
        VStack(alignment: .leading, spacing: 4) {
            TextField(title, text: $text)
                .focused($isFocused)
                .onChange(of: isFocused) { _, focused in
                    if !focused {
                        error = validation(text)
                    }
                }

            if let error {
                Text(error)
                    .font(.caption)
                    .foregroundStyle(.red)
            }
        }
    }
}

// Usage
ValidatedField(title: "Email", text: $email) { value in
    value.contains("@") ? nil : "Invalid email"
}

Option Picker

struct OptionPicker<T: Hashable>: View {
    let options: [T]
    @Binding var selection: T
    let label: (T) -> String

    var body: some View {
        HStack(spacing: 8) {
            ForEach(options, id: \.self) { option in
                Button {
                    selection = option
                } label: {
                    Text(label(option))
                        .padding(.horizontal, 16)
                        .padding(.vertical, 8)
                        .background(selection == option ? Color.accentColor : Color.secondary.opacity(0.2))
                        .foregroundStyle(selection == option ? .white : .primary)
                        .clipShape(Capsule())
                }
                .buttonStyle(.plain)
            }
        }
    }
}

Interactive Components

Swipe Actions

struct SwipeableRow<Content: View>: View {
    let content: Content
    let onDelete: () -> Void
    let onArchive: (() -> Void)?

    init(
        @ViewBuilder content: () -> Content,
        onDelete: @escaping () -> Void,
        onArchive: (() -> Void)? = nil
    ) {
        self.content = content()
        self.onDelete = onDelete
        self.onArchive = onArchive
    }

    var body: some View {
        content
            .swipeActions(edge: .trailing) {
                Button(role: .destructive, action: onDelete) {
                    Label("Delete", systemImage: "trash")
                }

                if let onArchive {
                    Button(action: onArchive) {
                        Label("Archive", systemImage: "archivebox")
                    }
                    .tint(.orange)
                }
            }
    }
}

Expandable Section

struct ExpandableSection<Content: View>: View {
    let title: String
    let content: Content
    @State private var isExpanded = false

    init(title: String, @ViewBuilder content: () -> Content) {
        self.title = title
        self.content = content()
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            Button {
                withAnimation(.snappy) {
                    isExpanded.toggle()
                }
            } label: {
                HStack {
                    Text(title)
                        .font(.headline)
                    Spacer()
                    Image(systemName: "chevron.right")
                        .rotationEffect(.degrees(isExpanded ? 90 : 0))
                }
                .contentShape(Rectangle())
            }
            .buttonStyle(.plain)

            if isExpanded {
                content
                    .padding(.top, 12)
            }
        }
    }
}

Data Display

Stat Card

struct StatCard: View {
    let title: String
    let value: String
    let trend: Trend?
    let icon: String?

    enum Trend {
        case up(String)
        case down(String)
        case neutral
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            HStack {
                Text(title)
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
                Spacer()
                if let icon {
                    Image(systemName: icon)
                        .foregroundStyle(.secondary)
                }
            }

            Text(value)
                .font(.title)
                .fontWeight(.semibold)

            if let trend {
                trendView(trend)
            }
        }
        .padding()
        .background(.background.secondary)
        .clipShape(RoundedRectangle(cornerRadius: 12))
    }

    @ViewBuilder
    private func trendView(_ trend: Trend) -> some View {
        switch trend {
        case .up(let value):
            Label(value, systemImage: "arrow.up")
                .font(.caption)
                .foregroundStyle(.green)
        case .down(let value):
            Label(value, systemImage: "arrow.down")
                .font(.caption)
                .foregroundStyle(.red)
        case .neutral:
            EmptyView()
        }
    }
}

Avatar

struct Avatar: View {
    let name: String
    let imageURL: URL?
    let size: CGFloat

    init(name: String, imageURL: URL? = nil, size: CGFloat = 40) {
        self.name = name
        self.imageURL = imageURL
        self.size = size
    }

    var body: some View {
        Group {
            if let imageURL {
                AsyncImage(url: imageURL) { image in
                    image.resizable().scaledToFill()
                } placeholder: {
                    initialsView
                }
            } else {
                initialsView
            }
        }
        .frame(width: size, height: size)
        .clipShape(Circle())
    }

    private var initialsView: some View {
        Text(initials)
            .font(.system(size: size * 0.4, weight: .medium))
            .foregroundStyle(.white)
            .frame(width: size, height: size)
            .background(color)
    }

    private var initials: String {
        name.split(separator: " ")
            .prefix(2)
            .compactMap { $0.first }
            .map(String.init)
            .joined()
            .uppercased()
    }

    private var color: Color {
        let colors: [Color] = [.blue, .purple, .orange, .green, .pink]
        let index = abs(name.hashValue) % colors.count
        return colors[index]
    }
}

Layout Components

Adaptive Grid

struct AdaptiveGrid<Content: View, Item: Identifiable>: View {
    let items: [Item]
    let minWidth: CGFloat
    let spacing: CGFloat
    let content: (Item) -> Content

    init(
        items: [Item],
        minWidth: CGFloat = 150,
        spacing: CGFloat = 16,
        @ViewBuilder content: @escaping (Item) -> Content
    ) {
        self.items = items
        self.minWidth = minWidth
        self.spacing = spacing
        self.content = content
    }

    var body: some View {
        LazyVGrid(
            columns: [GridItem(.adaptive(minimum: minWidth), spacing: spacing)],
            spacing: spacing
        ) {
            ForEach(items) { item in
                content(item)
            }
        }
    }
}

Aspect Ratio Container

struct AspectRatioContainer<Content: View>: View {
    let aspectRatio: CGFloat
    let content: Content

    init(
        _ aspectRatio: CGFloat = 1,
        @ViewBuilder content: () -> Content
    ) {
        self.aspectRatio = aspectRatio
        self.content = content()
    }

    var body: some View {
        GeometryReader { geometry in
            content
                .frame(
                    width: geometry.size.width,
                    height: geometry.size.width / aspectRatio
                )
        }
        .aspectRatio(aspectRatio, contentMode: .fit)
    }
}

Animation Components

Shimmer Loading

struct ShimmerView: View {
    @State private var phase: CGFloat = 0

    var body: some View {
        LinearGradient(
            colors: [
                .gray.opacity(0.3),
                .gray.opacity(0.1),
                .gray.opacity(0.3)
            ],
            startPoint: .leading,
            endPoint: .trailing
        )
        .mask(Rectangle())
        .offset(x: phase)
        .onAppear {
            withAnimation(.linear(duration: 1.5).repeatForever(autoreverses: false)) {
                phase = 200
            }
        }
    }
}

struct ShimmerModifier: ViewModifier {
    let isLoading: Bool

    func body(content: Content) -> some View {
        if isLoading {
            content.redacted(reason: .placeholder)
                .overlay(ShimmerView())
        } else {
            content
        }
    }
}

extension View {
    func shimmer(isLoading: Bool) -> some View {
        modifier(ShimmerModifier(isLoading: isLoading))
    }
}

Pulse Animation

struct PulseView: View {
    @State private var isPulsing = false

    var body: some View {
        Circle()
            .fill(.blue)
            .frame(width: 20, height: 20)
            .overlay(
                Circle()
                    .stroke(.blue, lineWidth: 2)
                    .scaleEffect(isPulsing ? 2 : 1)
                    .opacity(isPulsing ? 0 : 1)
            )
            .onAppear {
                withAnimation(.easeOut(duration: 1).repeatForever(autoreverses: false)) {
                    isPulsing = true
                }
            }
    }
}

Accessibility

Always Include

struct AccessibleButton: View {
    let title: String
    let icon: String
    let action: () -> Void

    var body: some View {
        Button(action: action) {
            Label(title, systemImage: icon)
        }
        .accessibilityLabel(title)
        .accessibilityHint("Double tap to \(title.lowercased())")
    }
}

Dynamic Type Support

struct AdaptiveStack<Content: View>: View {
    @Environment(\.dynamicTypeSize) var dynamicTypeSize
    let content: Content

    init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }

    var body: some View {
        if dynamicTypeSize >= .accessibility1 {
            VStack(alignment: .leading, content: { content })
        } else {
            HStack(content: { content })
        }
    }
}

Preview Organization

#Preview("Default") {
    Avatar(name: "John Doe")
}

#Preview("With Image") {
    Avatar(name: "Jane Smith", imageURL: URL(string: "https://example.com/avatar.jpg"))
}

#Preview("Large") {
    Avatar(name: "Bob Wilson", size: 80)
}

#Preview("Grid") {
    LazyVGrid(columns: [GridItem(.adaptive(minimum: 60))]) {
        ForEach(["Alice", "Bob", "Charlie", "Diana"], id: \.self) { name in
            Avatar(name: name)
        }
    }
    .padding()
}

Colors and Styling

Hierarchical Colors

SwiftUI provides semantic foreground styles that automatically adapt to context:

VStack(alignment: .leading) {
    Text("Primary text")
        .foregroundStyle(.primary)      // Full opacity, main content

    Text("Secondary text")
        .foregroundStyle(.secondary)    // Reduced opacity, supporting content

    Text("Tertiary text")
        .foregroundStyle(.tertiary)     // Further reduced, less important

    Text("Quaternary text")
        .foregroundStyle(.quaternary)   // Very subtle, decorative

    Text("Quinary text")
        .foregroundStyle(.quinary)      // Minimum visibility (iOS 17+)
}

Use cases:

• .primary - Titles, main content, important information
• .secondary - Subtitles, captions, supporting details
• .tertiary - Placeholders, hints, timestamps
• .quaternary - Dividers, subtle backgrounds
• .quinary - Decorative elements, barely visible accents

Hierarchical SF Symbols

// Automatic hierarchical rendering
Image(systemName: "square.stack.3d.up.fill")
    .symbolRenderingMode(.hierarchical)
    .foregroundStyle(.blue)

// Custom layer colors
Image(systemName: "person.crop.circle.badge.checkmark")
    .symbolRenderingMode(.palette)
    .foregroundStyle(.primary, .green)

Color Gradients

Apply gradients directly to colors for smooth visual effects:

// Gradient on foreground
Text("Gradient Text")
    .font(.largeTitle)
    .foregroundStyle(.blue.gradient)

// Gradient on shapes
Circle()
    .fill(.orange.gradient)

RoundedRectangle(cornerRadius: 12)
    .fill(.purple.gradient)

// Gradient on backgrounds
Text("Card")
    .padding()
    .background(.indigo.gradient)

Custom Gradients

// Linear gradient
LinearGradient(
    colors: [.blue, .purple],
    startPoint: .topLeading,
    endPoint: .bottomTrailing
)

// Radial gradient
RadialGradient(
    colors: [.white, .blue],
    center: .center,
    startRadius: 0,
    endRadius: 100
)

// Angular gradient
AngularGradient(
    colors: [.red, .yellow, .green, .blue, .purple, .red],
    center: .center
)

// Mesh gradient (iOS 18+)
MeshGradient(
    width: 3,
    height: 3,
    points: [
        [0, 0], [0.5, 0], [1, 0],
        [0, 0.5], [0.5, 0.5], [1, 0.5],
        [0, 1], [0.5, 1], [1, 1]
    ],
    colors: [
        .red, .orange, .yellow,
        .green, .blue, .purple,
        .pink, .mint, .cyan
    ]
)

Background Materials

Text("Blurred background")
    .padding()
    .background(.ultraThinMaterial)
    .clipShape(RoundedRectangle(cornerRadius: 12))

// Material options:
// .ultraThinMaterial - Most transparent
// .thinMaterial
// .regularMaterial
// .thickMaterial
// .ultraThickMaterial - Most opaque
// .bar - Navigation/tab bar style

Shadow Styles

// Drop shadow
Text("Shadowed")
    .shadow(color: .black.opacity(0.2), radius: 4, x: 0, y: 2)

// Inner shadow (using overlay)
RoundedRectangle(cornerRadius: 12)
    .fill(.white)
    .overlay {
        RoundedRectangle(cornerRadius: 12)
            .stroke(.black.opacity(0.1), lineWidth: 1)
    }

Best Practices

1. Use @ViewBuilder for flexible content composition
2. Provide sensible defaults for optional parameters
3. Support Dynamic Type and accessibility
4. Keep components focused - one responsibility per component
5. Use semantic colors (.primary, .secondary, .tertiary, .quaternary)
6. Use .gradient on colors for subtle depth
7. Test with previews in various configurations
8. Document complex components with usage examples