Mobile App Builder

Here's the SwiftUI implementation:

struct ProductListView: View {
    @StateObject private var viewModel = ProductListViewModel()
    
    var body: some View {
        List {
            ForEach(viewModel.products) { product in
                ProductRow(product: product)
                    .onAppear {
                        if product == viewModel.products.last {
                            viewModel.loadNextPage()
                        }
                    }
            }
            if viewModel.isLoading {
                ProgressView().frame(maxWidth: .infinity)
            }
        }
        .refreshable { await viewModel.refresh() }
        .task { await viewModel.loadInitialData() }
    }
}

Key patterns:

1. Pagination: Trigger loadNextPage() when last item appears — no manual 'load more' button
2. Pull-to-refresh: .refreshable gives native iOS pull gesture with proper loading indicator
3. Initial load: .task modifier loads data when view appears, automatically cancels on disappear
4. ViewModel: Uses @Published properties with @MainActor for thread-safe UI updates

Offline support: Cache API responses in Core Data. Show cached data immediately, refresh in background. Display a banner if showing stale data.

Use react-native-biometrics for cross-platform biometric auth:

import ReactNativeBiometrics from 'react-native-biometrics';

const biometrics = new ReactNativeBiometrics();

async function authenticateUser() {
  // Check availability
  const { available, biometryType } = await biometrics.isSensorAvailable();
  if (!available) return fallbackToPassword();
  
  // Prompt biometric
  const { success } = await biometrics.simplePrompt({
    promptMessage: 'Confirm your identity',
    cancelButtonText: 'Use password',
  });
  
  if (success) {
    // Generate keys for server verification
    const { publicKey } = await biometrics.createKeys();
    const { signature } = await biometrics.createSignature({
      promptMessage: 'Sign in',
      payload: serverChallenge,
    });
    await verifySignatureWithServer(signature, publicKey);
  }
}

Security notes:

1. Never store auth tokens in AsyncStorage — use react-native-keychain (backed by iOS Keychain / Android Keystore)
2. The server should verify the biometric signature, not trust a boolean from the client
3. Always provide a password fallback — biometrics can fail (wet fingers, masks)
4. On Android, handle the case where biometric enrollment changes (new fingerprint added = re-authenticate)