harmony 鸿蒙Managing Media Assets

  • 2023-10-30
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Managing Media Assets

Applications can call photoAccessHelper APIs to manage media assets (images and videos).

NOTE

  • Before you start, you need to obtain a PhotoAccessHelper instance and apply for required permissions. For details, see photoAccessHelper Overview.
  • By default, the PhotoAccessHelper instance obtained in photoAccessHelper Overview is used when photoAccessHelper APIs are used. If the code for obtaining the PhotoAccessHelper instance is not added, an error indicating that photoAccessHelper is not defined is reported.

To ensure application running efficiency, most PhotoAccessHelper APIs are asynchronously implemented in callback or promise mode. The following code samples use promise-based APIs. For details about the APIs, see Album Management.

Obtaining the Specified Media Assets

You can obtain media assets by media type, date, or album name.

Use PhotoAccessHelper.getAssets with the FetchOptions object to specify search criteria. Unless otherwise specified, all the media assets to be obtained in this document exist in the database. If no media asset is obtained when the sample code is executed, check whether the media assets exist in the database.

To obtain the object at the specified position (for example, the first, the last, or object with the specified index) in the result set, use FetchResult.

Prerequisites

  • A PhotoAccessHelper instance is obtained.
  • The application has the ohos.permission.READ_IMAGEVIDEO permission.
  • The dataSharePredicates module is imported.

Obtaining an Image or Video by Name

Example: Obtain the image test.jpg.

import dataSharePredicates from '@ohos.data.dataSharePredicates';
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
  predicates.equalTo(photoAccessHelper.PhotoKeys.DISPLAY_NAME, 'test.jpg');
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: [],
    predicates: predicates
  };
  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOptions);
    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    console.info('getAssets photoAsset.displayName : ' + photoAsset.displayName);
    fetchResult.close();
  } catch (err) {
    console.error('getAssets failed with err: ' + err);
  }
}

Obtaining an Image or Video by URI

Example: Obtain the image based on the URI file://media/Photo/1/IMG_datetime_0001/displayName.jpg.

import dataSharePredicates from '@ohos.data.dataSharePredicates';
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
  let uri = 'file://media/Photo/1/IMG_datetime_0001/displayName.jpg' // The URI must exist.
  predicates.equalTo(photoAccessHelper.PhotoKeys.URI, uri.toString());
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: [],
    predicates: predicates
  };

  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOptions);
    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    console.info('getAssets photoAsset.uri : ' + photoAsset.uri);
    fetchResult.close();
  } catch (err) {
    console.error('getAssets failed with err: ' + err);
  }
}

Obtaining Images or Videos by Time

Example: Obtain the media assets added between 2022-06-01 and 2023-06-01.

import dataSharePredicates from '@ohos.data.dataSharePredicates';
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
  let startTime = Date.parse(new Date('2022-06-01').toString()) / 1000; // The value of the start time is the number of seconds elapsed since the Epoch time.
  let endTime = Date.parse(new Date('2023-06-01').toString()) / 1000;   // The value of the end time is the number of seconds elapsed since the Epoch time.
  let date_added: photoAccessHelper.PhotoKeys = photoAccessHelper.PhotoKeys.DATE_ADDED;
  predicates.between(date_added, startTime, endTime);
  predicates.orderByDesc(date_added);                                   // Sort the obtained records in descending order.
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: [date_added],                                         // The date_added attribute is not a default option and needs to be added.
    predicates: predicates
  };
  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOptions);
    console.info('getAssets count: ' + fetchResult.getCount());
    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    console.info('getAssets photoAsset.displayName : ' + photoAsset.displayName);
    fetchResult.close();
  } catch (err) {
    console.error('getAssets failed with err: ' + err);
  }
}

Obtaining an Image or Video Thumbnail

Use PhotoAsset.getThumbnail with the thumbnail size passed in to obtain the image or video thumbnail. The thumbnails offer a quick preview on images and videos.

Prerequisites

  • A PhotoAccessHelper instance is obtained.
  • The application has the ohos.permission.READ_IMAGEVIDEO permission.
  • The dataSharePredicates module is imported.

Obtaining the Thumbnail of an Image

Your application may need to obtain the thumbnail of an image or video for preview purposes.

Example: Obtain the thumbnail of 720 x 720 of an image.

How to Develop

  1. Set the fetch options.
  2. Call PhotoAccessHelper.getAssets to obtain image assets.
  3. Call FetchResult.getFirstObject to obtain the first image from the result set.
  4. Call PhotoAsset.getThumbnail to obtain the PixelMap of the thumbnail of the image.
import dataSharePredicates from '@ohos.data.dataSharePredicates';
import image from '@ohos.multimedia.image';
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: [],
    predicates: predicates
  };

  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOptions);
    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    console.info('getAssets photoAsset.displayName : ' + photoAsset.displayName);
    let size: image.Size = { width: 720, height: 720 };
    let pixelMap: image.PixelMap =  await photoAsset.getThumbnail(size);
    let imageInfo: image.ImageInfo = await pixelMap.getImageInfo()
    console.info('getThumbnail successful, pixelMap ImageInfo size: ' + JSON.stringify(imageInfo.size));
    fetchResult.close();
  } catch (err) {
    console.error('getThumbnail failed with err: ' + err);
  }
}

Creating a Media Asset

Use PhotoAccessHelper.createAsset to create a media asset.

Prerequisites

  • A PhotoAccessHelper instance is obtained.
  • The application has the ohos.permission.WRITE_IMAGEVIDEO permission.

Creating an Image or Video Asset

Example: Create an image asset.

How to Develop

  1. Set the file name and create createOption for setting attributes for the image asset to create.
  2. Call PhotoAccessHelper.createAsset to create an image asset.
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  try {
    let displayName: string = 'testPhoto' + Date.now() + '.jpg';
    let createOption: photoAccessHelper.PhotoCreateOptions = {
      subtype: photoAccessHelper.PhotoSubtype.DEFAULT
    };

    let photoAsset: photoAccessHelper.PhotoAsset = await phAccessHelper.createAsset(displayName, createOption);
    console.info('createAsset successfully, file displayName: ' + photoAsset.displayName);
  } catch (err) {
    console.error('createAsset failed, message = ', err);
  }
}

Creating a Media Asset Using a Security Component

Example: Create an image asset using a security component. When using a security component to create a media asset, you do not need to apply for the ohos.permission.WRITE_IMAGEVIDEO permission for your application. For details, see <SaveButton>.

How to Develop

  1. Set the attributes of the security component.
  2. Create a security component.
  3. Call PhotoAccessHelper.createAsset to create an image asset.
import photoAccessHelper from '@ohos.file.photoAccessHelper'
import fs from '@ohos.file.fs';

@Entry
@Component
struct Index {
  @State message: string = 'Hello World'
  @State saveButtonOptions: SaveButtonOptions = {
    icon: SaveIconStyle.FULL_FILLED,
    text: SaveDescription.SAVE_IMAGE,
    buttonType: ButtonType.Capsule
  } // Set the attributes of the security component.

  build() {
    Row() {
      Column() {
        Text(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
        SaveButton(this.saveButtonOptions) // Create a security component.
          .onClick(async (event, result: SaveButtonOnClickResult) => {
             if (result == SaveButtonOnClickResult.SUCCESS) {
               try {
                 let context = getContext();
                 let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);
                 let uri = await phAccessHelper.createAsset(photoAccessHelper.PhotoType.IMAGE, 'jpg'); // Create a media asset.
                 console.info('createAsset successfully, uri: ' + uri);
                 let file = await fs.open(uri, fs.OpenMode.READ_WRITE);
                 await fs.close(file);
               } catch (err) {
                 console.error('createAsset failed, message = ', err);
               }
             } else {
               console.error('SaveButtonOnClickResult createAsset failed');
             }
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}

Renaming a Media Asset

Set the PhotoAsset.displayName attribute to modify the file name (including the file name extension) displayed, and call PhotoAsset.commitModify to update the modification to the database.

Before renaming a file, use FetchResult to obtain the file.

Prerequisites

  • A PhotoAccessHelper instance is obtained.
  • The application has the ohos.permission.WRITE_IMAGEVIDEO and ohos.permission.READ_IMAGEVIDEO permissions.

Example: Rename the first file in the obtained image assets.

How to Develop

  1. Set the fetch options.
  2. Call PhotoAccessHelper.getAssets to obtain image assets.
  3. Call FetchResult.getFirstObject to obtain the first image from the obtained file assets.
  4. Call PhotoAsset.set to rename the image.
  5. Call PhotoAsset.commitModify to update the modified image attributes to the database.
import dataSharePredicates from '@ohos.data.dataSharePredicates';
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: ['title'],
    predicates: predicates
  };
  let newTitle = 'newTestPhoto';

  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOptions);
    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    let title: photoAccessHelper.PhotoKeys = photoAccessHelper.PhotoKeys.TITLE;
    let photoAssetTitle: photoAccessHelper.MemberType = photoAsset.get(title);
    console.info('getAssets photoAsset.title : ' + photoAssetTitle);
    photoAsset.set(title, newTitle);
    await photoAsset.commitModify();
    fetchResult.close();
  } catch (err) {
    console.error('commitModify failed with err: ' + err);
  }
}

Moving Media Assets to the Trash

You can use PhotoAccessHelper.deleteAssets to move files to the trash.

The files moved to the trash will be retained for 30 days, and automatically deleted permanently after 30 days. Before a file is deleted permanently from the trash, the user can restore it using the system application FileManager or Gallery.

Prerequisites

  • A PhotoAccessHelper instance is obtained.
  • The application has the ohos.permission.WRITE_IMAGEVIDEO and ohos.permission.READ_IMAGEVIDEO permissions.

Example: Move the first file in the result set to the trash.

How to Develop

  1. Set the fetch options.
  2. Call PhotoAccessHelper.getAssets to obtain image assets.
  3. Call FetchResult.getFirstObject to obtain the first image, that is, the image object to be moved to the trash.
  4. Call PhotoAccessHelper.deleteAssets to move the file to the trash.
import dataSharePredicates from '@ohos.data.dataSharePredicates';
import photoAccessHelper from '@ohos.file.photoAccessHelper';
const context = getContext(this);
let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);

async function example() {
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: [],
    predicates: predicates
  };

  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOptions);
    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    console.info('getAssets photoAsset.uri : ' + photoAsset.uri);
    await phAccessHelper.deleteAssets([photoAsset.uri]);
    fetchResult.close();
  } catch (err) {
    console.error('deleteAssets failed with err: ' + err);
  }
}

Using Picker to Select Media Assets

When a user needs to share files such as images and videos, use a specific API to start Gallery for the user to select the files to share. No permission is required for this API. Currently, UIAbility is used to start Gallery by the window component. The procedure is as follows:

  1. Import the picker and fs modules.
   import photoAccessHelper from '@ohos.file.photoAccessHelper';
   import fs from '@ohos.file.fs';
   import { BusinessError } from '@ohos.base';
  1. Create a PhotoSelectOptions instance.
   import photoAccessHelper from '@ohos.file.photoAccessHelper';
   
   const photoSelectOptions = new photoAccessHelper.PhotoSelectOptions();
  1. Set the file type and the maximum number of media files to select. For example, select a maximum of five images. For details about the media file types, see PhotoViewMIMETypes.
   import photoAccessHelper from '@ohos.file.photoAccessHelper';
   
   photoSelectOptions.MIMEType = photoAccessHelper.PhotoViewMIMETypes.IMAGE_TYPE; // Select images.
   photoSelectOptions.maxSelectNumber = 5; // Set the maximum number of images to select.
  1. Create a photoViewPicker instance and call PhotoViewPicker.select to open the Gallery page for the user to select files. After the files are selected, the PhotoSelectResult is returned.

The permission on the URIs returned by select() is read-only. Further operations can be performed on the files based on the URIs in PhotoSelectResult. Note that the URI cannot be directly used in the picker callback to open a file. You need to define a global variable to save the URI and use a button to trigger file opening.

If metadata needs to be obtained, you can use File management and File URI APIs to obtain file attribute information, such as the file size, access time, modification time, file name, and file path, based on the URI.

   import photoAccessHelper from '@ohos.file.photoAccessHelper';
   import { BusinessError } from '@ohos.base';
   
   let uris: Array<string> = [];
   const photoViewPicker = new photoAccessHelper.PhotoViewPicker();
   photoViewPicker.select(photoSelectOptions).then((photoSelectResult: photoAccessHelper.PhotoSelectResult) => {
     uris = photoSelectResult.photoUris;
     console.info('photoViewPicker.select to file succeed and uris are:' + uris);
   }).catch((err: BusinessError) => {
     console.error(`Invoke photoViewPicker.select failed, code is ${err.code}, message is ${err.message}`);
   })
  1. After the UI is returned from the Gallery page, use a button to trigger API calling. Use fs.openSync() to open the file based on the URI and obtain the FD. Note that the mode parameter of fs.openSync() must be fs.OpenMode.READ_ONLY.
   import fs from '@ohos.file.fs';
   
   let uri: string = '';
   let file = fs.openSync(uri, fs.OpenMode.READ_ONLY);
   console.info('file fd: ' + file.fd);
  1. Use fs.readSync() to read the file based on the FD. After the data is read, close the FD.
   import fs from '@ohos.file.fs';
   
   let buffer = new ArrayBuffer(4096);
   let readLen = fs.readSync(file.fd, buffer);
   console.info('readSync data to file succeed and buffer size is:' + readLen);
   fs.closeSync(file);

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