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HarmonyOS Application Development

Core Principles

• ArkTS First — Use ArkTS with strict type safety, no any or dynamic types
• Declarative UI — Build UI with ArkUI's declarative components and state management
• Stage Model — Use modern Stage model (UIAbility), not legacy FA model
• Distributed by Design — Leverage cross-device capabilities from the start
• Atomic Services — Consider atomic services and cards for lightweight experiences
• One-time Development — Design for multi-device adaptation (phone, tablet, watch, TV)

Hard Rules (Must Follow)

These rules are mandatory. Violating them means the skill is not working correctly.

No Dynamic Types

ArkTS prohibits dynamic typing. Never useany, type assertions, or dynamic property access.

// ❌ FORBIDDEN: Dynamic types
let data: any = fetchData();
let obj: object = {};
obj['dynamicKey'] = value;  // Dynamic property access
(someVar as SomeType).method();  // Type assertion

// ✅ REQUIRED: Strict typing
interface UserData {
  id: string;
  name: string;
}
let data: UserData = fetchData();

// Use Record for dynamic keys
let obj: Record<string, string> = {};
obj['key'] = value;  // OK with Record type

No Direct State Mutation

Never mutate @State/@Prop variables directly in nested objects. Use immutable updates.

// ❌ FORBIDDEN: Direct mutation
@State user: User = { name: 'John', age: 25 };

updateAge() {
  this.user.age = 26;  // UI won't update!
}

// ✅ REQUIRED: Immutable update
updateAge() {
  this.user = { ...this.user, age: 26 };  // Creates new object, triggers UI update
}

// For arrays
@State items: string[] = ['a', 'b'];

// ❌ FORBIDDEN
this.items.push('c');  // UI won't update

// ✅ REQUIRED
this.items = [...this.items, 'c'];

Stage Model Only

Always use Stage model (UIAbility). Never use deprecated FA model (PageAbility).

// ❌ FORBIDDEN: FA Model (deprecated)
// config.json with "pages" array
export default {
  onCreate() { ... }  // PageAbility lifecycle
}

// ✅ REQUIRED: Stage Model
// module.json5 with abilities configuration
import { UIAbility } from '@kit.AbilityKit';

export default class EntryAbility extends UIAbility {
  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    // Modern Stage model lifecycle
  }

  onWindowStageCreate(windowStage: window.WindowStage): void {
    windowStage.loadContent('pages/Index');
  }
}

Component Reusability

Extract reusable UI into @Component. No inline complex UI in build() methods.

// ❌ FORBIDDEN: Monolithic build method
@Entry
@Component
struct MainPage {
  build() {
    Column() {
      // 200+ lines of inline UI...
      Row() {
        Image($r('app.media.avatar'))
        Column() {
          Text(this.user.name)
          Text(this.user.email)
        }
      }
      // More inline UI...
    }
  }
}

// ✅ REQUIRED: Extract components
@Component
struct UserCard {
  @Prop user: User;

  build() {
    Row() {
      Image($r('app.media.avatar'))
      Column() {
        Text(this.user.name)
        Text(this.user.email)
      }
    }
  }
}

@Entry
@Component
struct MainPage {
  @State user: User = { name: 'John', email: 'john@example.com' };

  build() {
    Column() {
      UserCard({ user: this.user })
    }
  }
}

Quick Reference

When to Use What

State Decorator Selection

@State        → Component owns the state, triggers re-render on change
@Prop         → Parent passes value, child gets copy (one-way)
@Link         → Parent passes reference, child can modify (two-way)
@Provide      → Ancestor provides value to all descendants
@Consume      → Descendant consumes value from ancestor
@StorageLink  → Syncs with AppStorage, two-way binding
@StorageProp  → Syncs with AppStorage, one-way binding
@Observed     → Class decorator for observable objects
@ObjectLink   → Links to @Observed object in parent

Project Structure

Recommended Architecture

MyApp/
├── entry/                          # Main entry module
│   ├── src/main/
│   │   ├── ets/
│   │   │   ├── entryability/       # UIAbility definitions
│   │   │   │   └── EntryAbility.ets
│   │   │   ├── pages/              # Page components
│   │   │   │   ├── Index.ets
│   │   │   │   └── Detail.ets
│   │   │   ├── components/         # Reusable UI components
│   │   │   │   ├── common/         # Common components
│   │   │   │   └── business/       # Business-specific components
│   │   │   ├── viewmodel/          # ViewModels (MVVM)
│   │   │   ├── model/              # Data models
│   │   │   ├── service/            # Business logic services
│   │   │   ├── repository/         # Data access layer
│   │   │   ├── utils/              # Utility functions
│   │   │   └── constants/          # Constants and configs
│   │   ├── resources/              # Resources (strings, images)
│   │   └── module.json5            # Module configuration
│   └── build-profile.json5
├── common/                         # Shared library module
│   └── src/main/ets/
├── features/                       # Feature modules
│   ├── feature_home/
│   └── feature_profile/
└── build-profile.json5             # Project configuration

Layer Separation

┌─────────────────────────────────────┐
│           UI Layer (Pages)          │  ArkUI Components
├─────────────────────────────────────┤
│         ViewModel Layer             │  State management, UI logic
├─────────────────────────────────────┤
│         Service Layer               │  Business logic
├─────────────────────────────────────┤
│        Repository Layer             │  Data access abstraction
├─────────────────────────────────────┤
│    Data Sources (Local/Remote)      │  Preferences, RDB, Network
└─────────────────────────────────────┘

ArkUI Component Patterns

Basic Component Structure

import { router } from '@kit.ArkUI';

@Component
export struct ProductCard {
  // Props from parent
  @Prop product: Product;
  @Prop onAddToCart: (product: Product) => void;

  // Local state
  @State isExpanded: boolean = false;

  // Computed values (use getters)
  get formattedPrice(): string {
    return `¥${this.product.price.toFixed(2)}`;
  }

  // Lifecycle
  aboutToAppear(): void {
    console.info('ProductCard appearing');
  }

  aboutToDisappear(): void {
    console.info('ProductCard disappearing');
  }

  // Event handlers
  private handleTap(): void {
    router.pushUrl({ url: 'pages/ProductDetail', params: { id: this.product.id } });
  }

  private handleAddToCart(): void {
    this.onAddToCart(this.product);
  }

  // UI builder
  build() {
    Column() {
      Image(this.product.imageUrl)
        .width('100%')
        .aspectRatio(1)
        .objectFit(ImageFit.Cover)

      Text(this.product.name)
        .fontSize(16)
        .fontWeight(FontWeight.Medium)

      Text(this.formattedPrice)
        .fontSize(14)
        .fontColor('#FF6B00')

      Button('Add to Cart')
        .onClick(() => this.handleAddToCart())
    }
    .padding(12)
    .backgroundColor(Color.White)
    .borderRadius(8)
    .onClick(() => this.handleTap())
  }
}

List with LazyForEach

import { BasicDataSource } from '../utils/BasicDataSource';

class ProductDataSource extends BasicDataSource<Product> {
  private products: Product[] = [];

  totalCount(): number {
    return this.products.length;
  }

  getData(index: number): Product {
    return this.products[index];
  }

  addData(product: Product): void {
    this.products.push(product);
    this.notifyDataAdd(this.products.length - 1);
  }

  updateData(index: number, product: Product): void {
    this.products[index] = product;
    this.notifyDataChange(index);
  }
}

@Component
struct ProductList {
  private dataSource: ProductDataSource = new ProductDataSource();

  build() {
    List() {
      LazyForEach(this.dataSource, (product: Product, index: number) => {
        ListItem() {
          ProductCard({ product: product })
        }
      }, (product: Product) => product.id)  // Key generator
    }
    .lanes(2)  // Grid with 2 columns
    .cachedCount(4)  // Cache 4 items for smooth scrolling
  }
}

Custom Dialog

@CustomDialog
struct ConfirmDialog {
  controller: CustomDialogController;
  title: string = 'Confirm';
  message: string = '';
  onConfirm: () => void = () => {};

  build() {
    Column() {
      Text(this.title)
        .fontSize(20)
        .fontWeight(FontWeight.Bold)
        .margin({ bottom: 16 })

      Text(this.message)
        .fontSize(16)
        .margin({ bottom: 24 })

      Row() {
        Button('Cancel')
          .onClick(() => this.controller.close())
          .backgroundColor(Color.Gray)
          .margin({ right: 16 })

        Button('Confirm')
          .onClick(() => {
            this.onConfirm();
            this.controller.close();
          })
      }
    }
    .padding(24)
  }
}

// Usage
@Entry
@Component
struct MainPage {
  dialogController: CustomDialogController = new CustomDialogController({
    builder: ConfirmDialog({
      title: 'Delete Item',
      message: 'Are you sure you want to delete this item?',
      onConfirm: () => this.deleteItem()
    }),
    autoCancel: true
  });

  private deleteItem(): void {
    // Delete logic
  }

  build() {
    Button('Delete')
      .onClick(() => this.dialogController.open())
  }
}

State Management Patterns

ViewModel Pattern

// viewmodel/ProductViewModel.ets
import { Product } from '../model/Product';
import { ProductRepository } from '../repository/ProductRepository';

@Observed
export class ProductViewModel {
  products: Product[] = [];
  isLoading: boolean = false;
  errorMessage: string = '';

  private repository: ProductRepository = new ProductRepository();

  async loadProducts(): Promise<void> {
    this.isLoading = true;
    this.errorMessage = '';

    try {
      this.products = await this.repository.getProducts();
    } catch (error) {
      this.errorMessage = `Failed to load: ${error.message}`;
    } finally {
      this.isLoading = false;
    }
  }

  async addProduct(product: Product): Promise<void> {
    const created = await this.repository.createProduct(product);
    this.products = [...this.products, created];
  }
}

// pages/ProductPage.ets
@Entry
@Component
struct ProductPage {
  @State viewModel: ProductViewModel = new ProductViewModel();

  aboutToAppear(): void {
    this.viewModel.loadProducts();
  }

  build() {
    Column() {
      if (this.viewModel.isLoading) {
        LoadingProgress()
      } else if (this.viewModel.errorMessage) {
        Text(this.viewModel.errorMessage)
          .fontColor(Color.Red)
      } else {
        ForEach(this.viewModel.products, (product: Product) => {
          ProductCard({ product: product })
        }, (product: Product) => product.id)
      }
    }
  }
}

AppStorage for Global State

// Initialize in EntryAbility
import { AbilityConstant, UIAbility, Want } from '@kit.AbilityKit';

export default class EntryAbility extends UIAbility {
  onCreate(want: Want, launchParam: AbilityConstant.LaunchParam): void {
    // Initialize global state
    AppStorage.setOrCreate('isLoggedIn', false);
    AppStorage.setOrCreate('currentUser', null);
    AppStorage.setOrCreate('theme', 'light');
  }
}

// Access in components
@Entry
@Component
struct ProfilePage {
  @StorageLink('isLoggedIn') isLoggedIn: boolean = false;
  @StorageLink('currentUser') currentUser: User | null = null;
  @StorageProp('theme') theme: string = 'light';  // Read-only

  build() {
    Column() {
      if (this.isLoggedIn && this.currentUser) {
        Text(`Welcome, ${this.currentUser.name}`)
      } else {
        Button('Login')
          .onClick(() => {
            // After login
            this.isLoggedIn = true;
            this.currentUser = { id: '1', name: 'John' };
          })
      }
    }
  }
}

PersistentStorage for Preferences

// Initialize persistent storage
PersistentStorage.persistProp('userSettings', {
  notifications: true,
  darkMode: false,
  language: 'zh-CN'
});

@Entry
@Component
struct SettingsPage {
  @StorageLink('userSettings') settings: UserSettings = {
    notifications: true,
    darkMode: false,
    language: 'zh-CN'
  };

  build() {
    Column() {
      Toggle({ type: ToggleType.Switch, isOn: this.settings.notifications })
        .onChange((isOn: boolean) => {
          this.settings = { ...this.settings, notifications: isOn };
        })

      Toggle({ type: ToggleType.Switch, isOn: this.settings.darkMode })
        .onChange((isOn: boolean) => {
          this.settings = { ...this.settings, darkMode: isOn };
        })
    }
  }
}

Navigation Patterns

Router Navigation

import { router } from '@kit.ArkUI';

// Navigate to page
router.pushUrl({
  url: 'pages/Detail',
  params: { productId: '123' }
});

// Navigate with result
router.pushUrl({
  url: 'pages/SelectAddress'
}).then(() => {
  // Navigation complete
});

// Get params in target page
@Entry
@Component
struct DetailPage {
  @State productId: string = '';

  aboutToAppear(): void {
    const params = router.getParams() as Record<string, string>;
    this.productId = params?.productId ?? '';
  }
}

// Go back
router.back();

// Replace current page
router.replaceUrl({ url: 'pages/Home' });

// Clear stack and navigate
router.clear();
router.pushUrl({ url: 'pages/Login' });

Navigation Component (Recommended for HarmonyOS NEXT)

@Entry
@Component
struct MainPage {
  @Provide('navPathStack') navPathStack: NavPathStack = new NavPathStack();

  @Builder
  pageBuilder(name: string, params: object) {
    if (name === 'detail') {
      DetailPage({ params: params as DetailParams })
    } else if (name === 'settings') {
      SettingsPage()
    }
  }

  build() {
    Navigation(this.navPathStack) {
      Column() {
        Button('Go to Detail')
          .onClick(() => {
            this.navPathStack.pushPath({ name: 'detail', param: { id: '123' } });
          })
      }
    }
    .navDestination(this.pageBuilder)
    .title('Home')
  }
}

@Component
struct DetailPage {
  @Consume('navPathStack') navPathStack: NavPathStack;
  params: DetailParams = { id: '' };

  build() {
    NavDestination() {
      Column() {
        Text(`Product ID: ${this.params.id}`)
        Button('Back')
          .onClick(() => this.navPathStack.pop())
      }
    }
    .title('Detail')
  }
}

Network Requests

HTTP Client

import { http } from '@kit.NetworkKit';

interface ApiResponse<T> {
  code: number;
  message: string;
  data: T;
}

class HttpClient {
  private baseUrl: string = 'https://api.example.com';

  async get<T>(path: string): Promise<T> {
    const httpRequest = http.createHttp();

    try {
      const response = await httpRequest.request(
        `${this.baseUrl}${path}`,
        {
          method: http.RequestMethod.GET,
          header: {
            'Content-Type': 'application/json',
            'Authorization': `Bearer ${await this.getToken()}`
          },
          expectDataType: http.HttpDataType.OBJECT
        }
      );

      if (response.responseCode === 200) {
        const result = response.result as ApiResponse<T>;
        if (result.code === 0) {
          return result.data;
        }
        throw new Error(result.message);
      }
      throw new Error(`HTTP ${response.responseCode}`);
    } finally {
      httpRequest.destroy();
    }
  }

  async post<T, R>(path: string, data: T): Promise<R> {
    const httpRequest = http.createHttp();

    try {
      const response = await httpRequest.request(
        `${this.baseUrl}${path}`,
        {
          method: http.RequestMethod.POST,
          header: {
            'Content-Type': 'application/json',
            'Authorization': `Bearer ${await this.getToken()}`
          },
          extraData: JSON.stringify(data),
          expectDataType: http.HttpDataType.OBJECT
        }
      );

      const result = response.result as ApiResponse<R>;
      return result.data;
    } finally {
      httpRequest.destroy();
    }
  }

  private async getToken(): Promise<string> {
    return AppStorage.get('authToken') ?? '';
  }
}

export const httpClient = new HttpClient();

Distributed Capabilities

Cross-Device Data Sync

import { distributedKVStore } from '@kit.ArkData';

class DistributedStore {
  private kvManager: distributedKVStore.KVManager | null = null;
  private kvStore: distributedKVStore.SingleKVStore | null = null;

  async init(context: Context): Promise<void> {
    const config: distributedKVStore.KVManagerConfig = {
      context: context,
      bundleName: 'com.example.myapp'
    };

    this.kvManager = distributedKVStore.createKVManager(config);

    const options: distributedKVStore.Options = {
      createIfMissing: true,
      encrypt: false,
      backup: false,
      autoSync: true,  // Auto sync across devices
      kvStoreType: distributedKVStore.KVStoreType.SINGLE_VERSION,
      securityLevel: distributedKVStore.SecurityLevel.S1
    };

    this.kvStore = await this.kvManager.getKVStore('myStore', options);
  }

  async put(key: string, value: string): Promise<void> {
    await this.kvStore?.put(key, value);
  }

  async get(key: string): Promise<string | null> {
    try {
      return await this.kvStore?.get(key) as string;
    } catch {
      return null;
    }
  }

  // Subscribe to changes from other devices
  subscribe(callback: (key: string, value: string) => void): void {
    this.kvStore?.on('dataChange', distributedKVStore.SubscribeType.SUBSCRIBE_TYPE_ALL,
      (data: distributedKVStore.ChangeNotification) => {
        for (const entry of data.insertEntries) {
          callback(entry.key, entry.value.value as string);
        }
        for (const entry of data.updateEntries) {
          callback(entry.key, entry.value.value as string);
        }
      }
    );
  }
}

Device Discovery and Connection

import { distributedDeviceManager } from '@kit.DistributedServiceKit';

class DeviceManager {
  private deviceManager: distributedDeviceManager.DeviceManager | null = null;

  async init(context: Context): Promise<void> {
    this.deviceManager = distributedDeviceManager.createDeviceManager(
      context.applicationInfo.name
    );
  }

  getAvailableDevices(): distributedDeviceManager.DeviceBasicInfo[] {
    return this.deviceManager?.getAvailableDeviceListSync() ?? [];
  }

  startDiscovery(): void {
    const filter: distributedDeviceManager.DiscoveryFilter = {
      discoverMode: distributedDeviceManager.DiscoverMode.DISCOVER_MODE_PASSIVE
    };

    this.deviceManager?.startDiscovering(filter);

    this.deviceManager?.on('discoverSuccess', (data) => {
      console.info(`Found device: ${data.device.deviceName}`);
    });
  }

  stopDiscovery(): void {
    this.deviceManager?.stopDiscovering();
  }
}

Multi-Device Adaptation

Responsive Layout

import { BreakpointSystem, BreakPointType } from '../utils/BreakpointSystem';

@Entry
@Component
struct AdaptivePage {
  @StorageProp('currentBreakpoint') currentBreakpoint: string = 'sm';

  build() {
    GridRow({
      columns: { sm: 4, md: 8, lg: 12 },
      gutter: { x: 12, y: 12 }
    }) {
      GridCol({ span: { sm: 4, md: 4, lg: 3 } }) {
        // Sidebar - full width on phone, 1/3 on tablet, 1/4 on desktop
        Sidebar()
      }

      GridCol({ span: { sm: 4, md: 4, lg: 9 } }) {
        // Content - full width on phone, 2/3 on tablet, 3/4 on desktop
        MainContent()
      }
    }
  }
}

// Breakpoint system
export class BreakpointSystem {
  private static readonly BREAKPOINTS: Record<string, number> = {
    'sm': 320,   // Phone
    'md': 600,   // Foldable/Tablet
    'lg': 840    // Desktop/TV
  };

  static register(context: UIContext): void {
    context.getMediaQuery().matchMediaSync('(width >= 840vp)').on('change', (result) => {
      AppStorage.setOrCreate('currentBreakpoint', result.matches ? 'lg' : 'md');
    });

    context.getMediaQuery().matchMediaSync('(width >= 600vp)').on('change', (result) => {
      if (!result.matches) {
        AppStorage.setOrCreate('currentBreakpoint', 'sm');
      }
    });
  }
}

Testing

Unit Testing

import { describe, it, expect, beforeEach } from '@ohos/hypium';
import { ProductViewModel } from '../viewmodel/ProductViewModel';

export default function ProductViewModelTest() {
  describe('ProductViewModel', () => {
    let viewModel: ProductViewModel;

    beforeEach(() => {
      viewModel = new ProductViewModel();
    });

    it('should load products successfully', async () => {
      await viewModel.loadProducts();

      expect(viewModel.products.length).assertLarger(0);
      expect(viewModel.isLoading).assertFalse();
      expect(viewModel.errorMessage).assertEqual('');
    });

    it('should add product to list', async () => {
      const initialCount = viewModel.products.length;
      const newProduct: Product = { id: 'test', name: 'Test Product', price: 99 };

      await viewModel.addProduct(newProduct);

      expect(viewModel.products.length).assertEqual(initialCount + 1);
    });
  });
}

UI Testing

import { describe, it, expect } from '@ohos/hypium';
import { Driver, ON } from '@ohos.UiTest';

export default function ProductPageUITest() {
  describe('ProductPage UI', () => {
    it('should display product list', async () => {
      const driver = Driver.create();
      await driver.delayMs(1000);

      // Find and verify list exists
      const list = await driver.findComponent(ON.type('List'));
      expect(list).not().assertNull();

      // Verify list items
      const items = await driver.findComponents(ON.type('ListItem'));
      expect(items.length).assertLarger(0);
    });

    it('should navigate to detail on tap', async () => {
      const driver = Driver.create();

      // Find first product card
      const card = await driver.findComponent(ON.type('ProductCard'));
      await card.click();

      await driver.delayMs(500);

      // Verify navigation to detail page
      const detailTitle = await driver.findComponent(ON.text('Product Detail'));
      expect(detailTitle).not().assertNull();
    });
  });
}

Checklist

## Project Setup
- [ ] Stage model used (not FA model)
- [ ] module.json5 properly configured
- [ ] Permissions declared in module.json5
- [ ] Resource files organized (strings, images)

## Code Quality
- [ ] No `any` types in codebase
- [ ] All state decorated with proper decorators
- [ ] No direct mutation of @State objects
- [ ] Components extracted for reusability
- [ ] Lifecycle methods used appropriately

## UI/UX
- [ ] LazyForEach used for long lists
- [ ] Loading states implemented
- [ ] Error handling with user feedback
- [ ] Multi-device layouts with GridRow/GridCol
- [ ] Accessibility attributes added

## State Management
- [ ] Clear state ownership (component vs global)
- [ ] @Observed/@ObjectLink for nested objects
- [ ] PersistentStorage for user preferences
- [ ] AppStorage for app-wide state

## Performance
- [ ] Images optimized and cached
- [ ] Unnecessary re-renders avoided
- [ ] Network requests with proper error handling
- [ ] Background tasks properly managed

## Testing
- [ ] Unit tests for ViewModels
- [ ] UI tests for critical flows
- [ ] Edge cases covered

See Also

• reference/arkts.md — ArkTS language guide and restrictions
• reference/arkui.md — ArkUI components and styling
• reference/stage-model.md — Stage model architecture
• reference/distributed.md — Distributed capabilities guide
• templates/project-structure.md — Project template

Weekly Installs

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Jan 24, 2026

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