HarmonyOS 后台任务没有调用回调方法

setBackgroundTask() {
  // 后台任务
  let wantAgentInfo: wantAgent.WantAgentInfo = {
    // 点击通知后，将要执行的动作列表
    wants: [
      {
        bundleName: "com.xxx.xxxworld",
        abilityName: "EntryAbility"
      }
    ],
    // 点击通知后，动作类型
    actionType: wantAgent.OperationType.START_ABILITY,
    // 使用者自定义的一个私有值
    requestCode: 0,
    // 点击通知后，动作执行属性
    wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
  };

  try {
    // 通过wantAgent模块下getWantAgent方法获取WantAgent对象
    wantAgent.getWantAgent(wantAgentInfo).then((wantAgentObj: WantAgent) => {
      try {
        backgroundTaskManager.startBackgroundRunning(this.context,
          backgroundTaskManager.BackgroundMode.LOCATION, wantAgentObj, callback)
      } catch (error) {
        console.error(`Operation startBackgroundRunning failed. code is ${(error as BusinessError).code} message is ${(error as BusinessError).message}`);
      }
    });
  } catch (error) {
    console.error(`Operation getWantAgent failed. code is ${(error as BusinessError).code} message is ${(error as BusinessError).message}`);
  }
}
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为什么 这个后台任务没有调用 回调方法呢