Uniform Data Structs

When to Use

The Unified Data Management Framework (UDMF) provides uniform data structs for some uniform data types, for example the widget type (openharmony.form) used on the home screen.

Applications can directly use the uniform data structs in certain scenarios. For example, in the drag-and-drop operation across applications, you can write the data (encapsulated in a uniform struct) to be dragged to DragEvent. The target application (application requesting the data) reads the data from DragEvent and parses the data in the uniform data struct. Using uniform data structs for data interaction between applications effectively reduces the development workload in your app experience.

Uniform Data Structs

The following table lists the uniform data structs provided by the UDMF.

Constraints

The UDMF supports management of batch data records. Each data set cannot exceed 200 MB. The maximum size of a single attribute in PlainText, Hyperlink, or HTML is 20 MB.

Available APIs

The UDMF provides a UnifiedData object to encapsulate multiple UnifiedRecords. UnifiedRecord is an abstract definition of data supported by the UDMF, for example, a text or an image. The data records in a UnifiedRecord object are of the UniformDataType type.

The following table lists the commonly used APIs for managing uniform data structs. For more information, see Unified Data Channel and Uniform Type Descriptor.

How to Develop

The following describes how to encapsulate an image and a plaint text into an object in a uniform data struct and manage the data.

1. Import the @ohos.data.unifiedDataChannel and @ohos.data.uniformTypeDescriptor modules.

   import unifiedDataChannel from '@ohos.data.unifiedDataChannel';
   import uniformTypeDescriptor from '@ohos.data.uniformTypeDescriptor';
   

2. Create an image object and create a UnifiedData instance with the image object.

   • Create an image object.

     let image = new unifiedDataChannel.Image();
     

   • Modify the image object attributes.

     // The image object has the imageUri attribute.
     image.imageUri = '...';
     

   • Access the image object attribute.

     console.info(`imageUri = ${image.imageUri}`);
     

   • Create a UnifiedData instance with the image object.

     let unifiedData = new unifiedDataChannel.UnifiedData(image);
     

3. Create a plain text data record and add it to the UnifiedData instance created.

   let plainText = new unifiedDataChannel.PlainText();
   plainText.textContent = 'this is textContent of plainText';
   plainText.abstract = 'abstract of plainText';
   plainText.details = {
     plainKey1: 'plainValue1',
     plainKey2: 'plainValue2',
   };
   unifiedData.addRecord(plainText);
   

4. Obtain all data records in this UnifiedData instance.

   let records = unifiedData.getRecords();
   

5. Traverse each record, determine the data type, and convert the data type into a child class object to obtain the original data.

   for (let i = 0; i < records.length; i ++) {
     // Obtain the type of each data record.
     let type = records[i].getType();
     switch (type) {
       case uniformTypeDescriptor.UniformDataType.IMAGE:
         // Convert the data type to obtain the image.
         let image = records[i] as unifiedDataChannel.Image;
         break;
       case uniformTypeDescriptor.UniformDataType.PLAIN_TEXT:
         // Convert the data to obtain the plain text.
         let plainText = records[i] as unifiedDataChannel.PlainText;
         break;
       default:
         break;
     }
   }