1.在module.json5中
    "requestPermissions": [
      {"name": "ohos.permission.INTERNET"},
      {"name": "ohos.permission.GET_BUNDLE_INFO"},
      {"name": "ohos.permission.KEEP_BACKGROUND_RUNNING"}
    ],

  "pages": "$profile:main_pages",
    "abilities": [
      {
        "name": "EntryAbility",
        "backgroundModes": [
          "dataTransfer"       // 对应 BackgroundMode.DATA_TRANSFER
        ],



2.在EntryAblility中
  async onForeground(): Promise<void> {
    // Ability has brought to foreground
    hilog.info(DOMAIN, 'testTag', '%{public}s', 'Ability onForeground');
    try {
      const wantAgentInfo: wantAgent.WantAgentInfo = {
        wants: [{ bundleName: 'com.xxx.xxx', abilityName: 'EntryAbility' }],
        actionType: wantAgent.OperationType.START_ABILITY,
        requestCode: 0,
        actionFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
      };

      const wantAgentObj = await wantAgent.getWantAgent(wantAgentInfo);
      const taskTypes = ['dataTransfer']; // 或 ['audioPlayback'], ['audioRecording'] 等
      const res = await backgroundTaskManager.startBackgroundRunning(this.context, backgroundTaskManager.BackgroundMode.DATA_TRANSFER, wantAgentObj);
      // console.info('后台长时任务已申请, notificationId:', res.notificationId);
    } catch (e) {
      console.error('申请后台长时任务失败:', JSON.stringify(e));
    }
  }