Core Implementation Principles and Development Steps of HarmonyOS “Tap-to-Share” Feature

June 27, 2025

This content originally appeared on DEV Community and was authored by 魔眼天王

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I. Technical Principles

HarmonyOS “Tap-to-Share” leverages NFC + Distributed Soft Bus dual engines, with core architecture:

Physical Layer (NFC Chip) ↔ Protocol Layer (HMS Core) ↔ Distributed Layer (Soft Bus)

NFC Trigger: Integrated NFC sensing area on device top, communicating via ISO/IEC 14443 protocol within 10cm range
Distributed Communication: Establishes secure channels through RPC framework with AES-256-CBC end-to-end encryption
ArkUI Rendering: Dynamically generates share cards using declarative UI framework for cross-device synchronization

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II. Development Implementation

1. Environment Configuration

// Check device compatibility  
if (canIUse('SystemCapability.Collaboration.HarmonyShare')) {  
  // Initialize distributed capabilities  
  await distributedData.init();  
}

2. Event Registration

// Register tap-to-share listener  
harmonyShare.on('knockShare', (event) => {  
  const target = event.sharableTarget;  
  handleShare(target);  
});  

// Remove listener on page unload  
onPageHide(() => {  
  harmonyShare.off('knockShare');  
});

3. Data Construction & Trigger

// Build share data object  
const shareData = new ShareData({  
  type: ShareType.LINK,  
  content: 'https://example.com',  
  thumbnail: fileUri.getUriFromPath('/images/share.png'),  
  title: 'Project Proposal',  
  description: '2025 Technical Roadmap'  
});  

// Initiate tap-to-share  
const targetDevice = await findNearbyDevice();  
targetDevice.share(shareData);

4. Result Handling

// Monitor transfer status  
distributedData.on('transferStatus', (status) => {  
  if (status === 'SUCCESS') {  
    showToast('Transfer completed');  
  } else {  
    showError('Transfer failed');  
  }  
});

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III. Technical Advantages

Millisecond Device Discovery

Utilizes NFC ATR protocol for device fingerprinting (<80ms response)

Secure Transmission

Device fingerprint mutual authentication (TEE-based)
Fragmented encryption (128B chunks with dynamic key rotation)

Smart Context Recognition

   graph LR  
   A[Tap] --> B{Content Identification}  
   B -->|Image| C[Launch Gallery]  
   B -->|Text| D[Launch Notes]  
   B -->|File| E[Launch File Manager]

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IV. Performance Metrics

Scenario	Transfer Speed	Success Rate	Latency
1MB Image	24 MB/s	99.8%	120ms
10MB Document	18 MB/s	99.5%	150ms
100MB Video	12 MB/s	98.2%	210ms

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V. Use Cases

Cross-Device Sharing

Phone → Tablet: Design files with layer preservation
PC → Phone: Meeting notes auto-sync to Notes app

Smart Device Control

   // Connect to smart lighting  
   const device = await findDeviceByType('LIGHT');  
   await device.executeCommand('setBrightness', 80);

Contactless Payments

Phone tap POS for payments (no app launch)
Public transit card tap for instant recharge

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VI. Comparative Advantages

Aspect	Traditional NFC	HarmonyOS Tap-to-Share
Interaction	Requires dedicated APP	System-native support
Efficiency	Protocol-dependent	Direct device connection
Scalability	Single-function	Dynamic capability expansion
Security	Device-level auth	App+User dual-factor

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VII. Implementation Notes

Permission Management

   // Request necessary permissions  
   requestPermissions(['ohos.permission.NFC', 'ohos.permission.INTERNET']);

Error Handling

   try {  
     await device.connect();  
   } catch (e) {  
     if (e.code === 'DEVICE_BUSY') {  
       showToast('Device busy, retry');  
     }  
   }

Optimization Tips

Use shareData.compress() for content reduction
Chunk large files (≤500KB per fragment)

This content originally appeared on DEV Community and was authored by 魔眼天王

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