DEV Community

lyc233333
lyc233333

Posted on

Hongmeng UTD Detailed Explanation: Cross-end Collaboration Key for Standardized Data Types🔑

Hongmeng Next's UTD (Uniform Type Descriptor) solves the problem of cross-application and cross-device data identification by standardizing data types.This article uses streamlined language to analyze the core concepts and practical points~

1. UTD core: "Global unique ID card" of data type🆔

Definition and Function

  • Unique ID: Each data type has a unique ID (such as general.image) to avoid type ambiguity
  • Hydraft Structure: Classification system similar to file directories (media > image > photo)
  • Cross-end compatibility: Unify application/device's awareness of data types to improve interaction efficiency

Core attribute table

Properties Description Example
typeId Unique Identifier com.example.custom.pdf
belongingTo Parent type (multi-level) general.document
description Type Description "Custom PDF Document"
fileExtensions Associated file suffix [".pdf", ".pdfx"]
mimeType MIME type "application/pdf"

2. Preset type: System-level data classification "infrastructure" 🚧

Common hierarchy examples 

media  
├─ image          (general.image)  
│  ├─ photo       (image.photo)  
│  └─ graphic     (image.graphic)  
└─ video          (general.video)  
    └─ movie      (video.movie)
Enter fullscreen mode Exit fullscreen mode

Typical application scenarios

  • File Sharing: The system automatically matches applications that support general.image based on UTD (such as albums, editors)
  • Data synchronization: When transmitting across devices, UTD ensures that the receiver correctly parses the video.movie type videos

3. Custom type: "movable type module" that extends system capabilities🔧

Create steps

  1. Define Type 
   import { TypeDescriptor } from '@ohos.uniformTypeDescriptor';  
   const customType = new TypeDescriptor({  
     typeId: 'com.example.app.custom_audio',  
belongingTo: ['general.audio'], // Inherited from audio type
description: 'Custom lossless audio',
     fileExtensions: ['.lossless'],  
     mimeType: 'audio/x-lossless'  
   });
Enter fullscreen mode Exit fullscreen mode
  1. Register to the system 
   TypeDescriptor.register(customType);
Enter fullscreen mode Exit fullscreen mode
  1. Cross-app use 
// Sender
   const data = new File('music.lossless', customType.typeId);  
   featureAbility.startAbility({  
     action: 'android.intent.action.SEND',  
     type: customType.mimeType,  
     extra: { 'android.intent.extra.STREAM': data  
   });  

// Recipient
   const receivedType = Ability.getWant().type;  
   if (TypeDescriptor.isCompatible(receivedType, 'com.example.app.custom_audio')) {  
     processLosslessAudio();  
   }
Enter fullscreen mode Exit fullscreen mode

4. Compatibility design: Let custom types "integrate into the system ecosystem"🌐

1. Parent-child type compatibility 

// Check whether it belongs to a certain parent type
TypeDescriptor.isAncestor('general.image', 'image.photo'); // Return true
Enter fullscreen mode Exit fullscreen mode

2. Cross-device transmission adaptation 

// Automatically convert to common type during transmission
if (device.type === 'wearable') {  
  const fallbackType = TypeDescriptor.getFallbackType('com.example.custom_audio');  
sendDataWithType(fallbackType); // Automatic downgrading to general.audio
}
Enter fullscreen mode Exit fullscreen mode

3. Conflict resolution strategy

Scenarios Solutions
Third-party applications define the type of the same name Priority is given priority to using the system preset type, and custom types must be declared priority
Type attribute changes Release a new version through TypeDescriptor.update()

5. Practical cases: Customize the "engineering drawing" type📃

1. Type definition 

const cadType = new TypeDescriptor({  
  typeId: 'com.engineer.app.cad_draw',  
belongingTo: ['general.document', 'engineering'], // Multiple parent types
description: 'CAD engineering drawings',
  fileExtensions: ['.dwg', '.dxf'],  
  mimeType: 'application/cad'  
});
Enter fullscreen mode Exit fullscreen mode

2. Cross-application collaboration 

// CAD editor sends drawings
const drawing = new File('project.dwg', cadType.typeId);  
ability.startAbility({  
  action: 'com.engineer.app.ACTION_OPEN_CAD',  
  type: cadType.mimeType,  
  extra: { 'cad_data': drawing }  
});  

// Approve application acceptance and preview
if (TypeDescriptor.isCompatible(want.type, cadType.typeId)) {  
  const renderer = new CadRenderer(want.extra['cad_data']);  
  renderer.preview();  
}
Enter fullscreen mode Exit fullscreen mode

Summary: UTD uses the "Three Principles"

  1. Prioritative reuse: Try to use system preset types (such as general.image) to avoid repeated wheel creation
  2. Clear hierarchy: Custom types need to be clearly attributed (such as engineering.cad belongs to general.document)
  3. Compatible Design: Consider cross-default strategy for type across devices and applications

Top comments (0)