Managing Media Asset Change Notifications

The photoAccessHelper module provides APIs for listening for media asset (image, video, and album) changes.

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.

The APIs related to media asset change notifications can be called asynchronously only in callback mode. This topic describes how to use some APIs. For more information about the APIs, see Album Management. 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.

Listening for the Specified URI

Use registerChange to listen for the specified URI. When the observed object changes, the value of the listener callback will be returned.

Listening for a PhotoAsset

Register a listener for the specified PhotoAsset. When the observed PhotoAsset changes, the listener callback will be invoked to return the change.

Prerequisites

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

Example: Listener for changes of an image. When the image is favorited, the listener callback will be invoked.

How to Develop

1. Obtain a media asset.
2. Register a listener for a PhotoAsset.
3. Add the PhotoAsset to Favorites.

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 fileAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
    console.info('getAssets fileAsset.uri : ' + fileAsset.uri);

    let onCallback = (changeData: photoAccessHelper.ChangeData) => {
      console.info('onCallback successfully, changData: ' + JSON.stringify(changeData));
    }
    phAccessHelper.registerChange(fileAsset.uri, false, onCallback);
    await fileAsset.setFavorite(true);
    fetchResult.close();
  } catch (err) {
    console.error('onCallback failed with err: ' + err);
  }
}

Listening for an Album

Register a listener for an album. When the observed album changes, the listener callback will be invoked to return the change.

Prerequisites

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

Example: Listener for a user album. When the album is renamed, the listener callback will be invoked.

How to Develop

1. Obtain a user album.
2. Register a listener for the user album.
3. Rename the user album.

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 albumName: photoAccessHelper.AlbumKeys = photoAccessHelper.AlbumKeys.ALBUM_NAME;
  predicates.equalTo(albumName, 'albumName');
  let fetchOptions: photoAccessHelper.FetchOptions = {
    fetchColumns: [],
    predicates: predicates
  };

  try {
    let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.Album> = await phAccessHelper.getAlbums(photoAccessHelper.AlbumType.USER, photoAccessHelper.AlbumSubtype.USER_GENERIC, fetchOptions);
    let album: photoAccessHelper.Album = await fetchResult.getFirstObject();
    console.info('getAlbums successfullyfully, albumName: ' + album.albumUri);

    let onCallback = (changeData: photoAccessHelper.ChangeData) => {
      console.info('onCallback successfully, changData: ' + JSON.stringify(changeData));
    }
    phAccessHelper.registerChange(album.albumUri, false, onCallback);
    album.albumName = 'newAlbumName' + Date.now();
    await album.commitModify();
    fetchResult.close();
  } catch (err) {
    console.error('onCallback failed with err: ' + err);
  }
}

Fuzzy Listening

You can set forChildUris to true to enable fuzzy listening.

If uri is an album URI, the value true of forChildUris enables listening for the changes of the files in the album, and the value false enables listening for only the changes of the album itself.

If uri is the URI of a photoAsset, there is no difference between true and false for forChildUris.

If uri is DefaultChangeUri, forChildUris must be set to true. If forChildUris is false, the URI cannot be found and no notification can be received.

Listening for All PhotoAssets

Register a listener for all PhotoAssets. When a PhotoAsset changes, the listener callback will be invoked.

Prerequisites

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

Example: Register a listener for all PhotoAssets. When a PhotoAsset is favorited, the listener callback will be invoked.

How to Develop

1. Register a listener for all PhotoAssets.
2. Obtain a media asset.
3. Add the media asset to Favorites.

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 onCallback = (changeData: photoAccessHelper.ChangeData) => {
    console.info('onCallback successfully, changData: ' + JSON.stringify(changeData));
  }
  phAccessHelper.registerChange(photoAccessHelper.DefaultChangeUri.DEFAULT_PHOTO_URI, true, onCallback);
  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 photoAsset.setFavorite(true);
    fetchResult.close();
  } catch (err) {
    console.error('onCallback failed with err: ' + err);
  }
}

Unregistering Listening for a URI

Use unRegisterChange to unregister the listening for the specified URI. Multiple listeners can be registered for a URI. If multiple listener callbacks exist, you can unregister a listener callback registered. If callback is not specified, all listeners of the URI will be unregistered.

Prerequisites

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

Example: Unregister listening for an image. After that, the unregistered listener callback will not be invoked when the image favorite status is changed.

How to Develop

1. Obtain a media asset.
2. Unregister listening for the URI of the media asset obtained.
3. Add the media asset to Favorites.

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.uri : ' + photoAsset.uri);

    let onCallback1 = (changeData: photoAccessHelper.ChangeData) => {
      console.info('onCallback1, changData: ' + JSON.stringify(changeData));
    }
    let onCallback2 = (changeData: photoAccessHelper.ChangeData) => {
      console.info('onCallback2, changData: ' + JSON.stringify(changeData));
    }
    phAccessHelper.registerChange(photoAsset.uri, false, onCallback1);
    phAccessHelper.registerChange(photoAsset.uri, false, onCallback2);
    phAccessHelper.unRegisterChange(photoAsset.uri, onCallback1);
    await photoAsset.setFavorite(true);
    fetchResult.close();
  } catch (err) {
    console.error('onCallback failed with err: ' + err);
  }
}

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