SwiftUI Layout Best Practices Reference

Table of Contents

• Relative Layout Over Constants
• Context-Agnostic Views
• Own Your Container
• Layout Performance
• View Logic and Testability
• Full-Width Views
• Action Handlers
• Summary Checklist

Relative Layout Over Constants

Use dynamic layout calculations instead of hard-coded values.

// Good - relative to actual layout
GeometryReader { geometry in
    VStack {
        HeaderView()
            .frame(height: geometry.size.height * 0.2)
        ContentView()
    }
}

// Avoid - magic numbers that don't adapt
VStack {
    HeaderView()
        .frame(height: 150)  // Doesn't adapt to different screens
    ContentView()
}

Why: Hard-coded values don't account for different screen sizes, orientations, or dynamic content (like status bars during phone calls).

Context-Agnostic Views

Views should work in any context. Never assume presentation style or screen size.

// Good - adapts to given space
struct ProfileCard: View {
    let user: User
    
    var body: some View {
        VStack {
            Image(user.avatar)
                .resizable()
                .aspectRatio(contentMode: .fit)
            Text(user.name)
            Spacer()
        }
        .padding()
    }
}

// Avoid - assumes full screen
struct ProfileCard: View {
    let user: User
    
    var body: some View {
        VStack {
            Image(user.avatar)
                .frame(width: UIScreen.main.bounds.width)  // Wrong!
            Text(user.name)
        }
    }
}

Why: Views should work as full screens, modals, sheets, popovers, or embedded content.

Own Your Container

Custom views should own static containers but not lazy/repeatable ones.

// Good - owns static container
struct HeaderView: View {
    var body: some View {
        HStack {
            Image(systemName: "star")
            Text("Title")
            Spacer()
        }
    }
}

// Avoid - missing container
struct HeaderView: View {
    var body: some View {
        Image(systemName: "star")
        Text("Title")
        // Caller must wrap in HStack
    }
}

// Good - caller owns lazy container
struct FeedView: View {
    let items: [Item]
    
    var body: some View {
        LazyVStack {
            ForEach(items) { item in
                ItemRow(item: item)
            }
        }
    }
}

Layout Performance

Avoid Layout Thrash

Minimize deep view hierarchies and excessive layout dependencies.

// Bad - deep nesting, excessive layout passes
VStack {
    HStack {
        VStack {
            HStack {
                VStack {
                    Text("Deep")
                }
            }
        }
    }
}

// Good - flatter hierarchy
VStack {
    Text("Shallow")
    Text("Structure")
}

Avoid excessive GeometryReader and preference chains:

// Bad - multiple geometry readers cause layout thrash
GeometryReader { outerGeometry in
    VStack {
        GeometryReader { innerGeometry in
            // Layout recalculates multiple times
        }
    }
}

// Good - single geometry reader or use alternatives (iOS 17+)
containerRelativeFrame(.horizontal) { width, _ in
    width * 0.8
}

Gate frequent geometry updates:

// Bad - updates on every pixel change
.onPreferenceChange(ViewSizeKey.self) { size in
    currentSize = size
}

// Good - gate by threshold
.onPreferenceChange(ViewSizeKey.self) { size in
    let difference = abs(size.width - currentSize.width)
    if difference > 10 {  // Only update if significant change
        currentSize = size
    }
}

View Logic and Testability

Keep Business Logic in Services and Models

Business logic belongs in services and models, not in views. Views should stay simple and declarative — orchestrating UI state, not implementing business rules. This makes logic independently testable without requiring view instantiation.

iOS 17+: Use @Observable with @State.

@Observable
final class AuthService {
    var email = ""
    var password = ""
    var isValid: Bool {
        !email.isEmpty && password.count >= 8
    }

    func login() async throws {
        // Business logic here — testable without the view
    }
}

struct LoginView: View {
    @State private var authService = AuthService()

    var body: some View {
        Form {
            TextField("Email", text: $authService.email)
            SecureField("Password", text: $authService.password)
            Button("Login") {
                Task {
                    try? await authService.login()
                }
            }
            .disabled(!authService.isValid)
        }
    }
}

For iOS 16 and earlier, use ObservableObject with @StateObject -- see state-management.md for the legacy pattern.

Avoid embedding business logic directly in view closures (e.g., validation checks inside a Button action). This makes logic untestable without view instantiation.

Note: This is about making business logic testable, not about enforcing a specific architecture. The key is that logic lives outside views where it can be tested independently.

Full-Width Views

When a single view needs to fill the available width, use .frame(maxWidth: .infinity, alignment:) instead of wrapping it in a stack with a Spacer.

// Good - frame modifier
Text("Hello")
    .frame(maxWidth: .infinity, alignment: .leading)

// Avoid - unnecessary stack and spacer
HStack {
    Text("Hello")
    Spacer()
}

Why: .frame(maxWidth:alignment:) is a single modifier that clearly communicates intent. Wrapping in an HStack with a Spacer adds an extra container to the view hierarchy for no benefit.

Action Handlers

Separate layout from logic. View body should reference action methods, not contain inline logic.

// Good - action references method
Button("Publish Project", action: publishService.handlePublish)

// Avoid - multi-line logic in closure
Button("Publish Project") {
    isLoading = true
    apiService.publish(project) { result in /* ... */ }
}

Summary Checklist

• [ ] Use relative layout over hard-coded constants
• [ ] Views work in any context (don't assume screen size)
• [ ] Custom views own static containers
• [ ] Avoid deep view hierarchies (layout thrash)
• [ ] Gate frequent geometry updates by thresholds
• [ ] Business logic kept in services and models (not in views)
• [ ] Action handlers reference methods, not inline logic
• [ ] Use .frame(maxWidth: .infinity, alignment:) for full-width views (not HStack + Spacer)
• [ ] Avoid excessive GeometryReader usage
• [ ] Use containerRelativeFrame() when appropriate