Expo开发工具：在后台运行开发应用程序

Question

这是我第一次在 Expo 中开发，我正在构建应用程序来跟踪位置并使用 node.js 每 5 秒将数据发送到服务器。我正在使用来自世博会的TaskManager API，我会跟踪所有内容，并且它可以正常工作，我正在获取数据。但是当我将我的应用程序放在后台时，它会停止console.log(data)。

这是否应该在后台任务中运行（TaskManager），即使在使用 Expo Dev Tool 的开发环境中，还是需要在它工作之前进入生产模式？

当我像这样将应用程序切换到后台模式时，我的console.log 停止工作。

我的示例代码 App.js

const LOCATION_TRACKER = 'background-task-location';

export default class App extends Component {
     state = {
      mapRegion: null,
      hasLocationPermissions: false,
      locationResult: null,
      marker: {
        latitude: 0,
        longitude: 0
      },
      latitude: 0,
      longitude: 0,
      location: null,
      errorMessage: null
    }


   componentDidMount() {
    //this.watchCurLocation();
    this.onLoad();  

   }

   //init task manager
  onLoad = async() => {
    let isRegistered = await TaskManager.isTaskRegisteredAsync(LOCATION_TRACKER)
    if (!isRegistered) await Location.startLocationUpdatesAsync(LOCATION_TRACKER, {
      accuracy: Location.Accuracy.High,
      /* after edit */
      timeInterval: 2500,
      distanceInterval: 5,
    })
  }


onPress = async () => {
    console.log('waiting')
    await Location.startLocationUpdatesAsync(LOCATION_TRACKER, {
      accuracy: Location.Accuracy.High,
      timeInterval: 5000,
      distanceInterval: 5

    });

    console.log('waiting for get task option');
    //const data = await TaskManager.getTaskOptionsAsync(LOCATION_TRACKER)
    //console.log(data);

  };


watchCurLocation = () =>{
    this.onPress();
    setTimeout(() => {
      this.watchCurLocation();
    }, 5000);
  }


}


TaskManager.defineTask(LOCATION_TRACKER, ({ data, error }) => {
  if (error) {
    console.log(error)
    // Error occurred - check `error.message` for more details.
    return;
  }
  if (data) {
    const { locations } = data;
    console.log(data)
    // do something with the locations captured in the background
  }
});

Answer 1

在 Android Oreo 及更高版本中，应用程序将不会在后台运行此类任务。 应有的限制：https://developer.android.com/about/versions/oreo/background#services

您必须在系统托盘中显示一些通知才能让跟踪器在后台工作。

a) 您可以尝试添加使用频道的通知，而无需弹出 expo

https://docs.expo.io/versions/v32.0.0/guides/notification-channels

或 b) 弹出 expo 并添加一个前台服务，该服务将在应用程序进入后台时启动

与此类似，只是为了了解一下：

public class ForegroundService extends Service {
///....

   public  void toForeground(){ 
        startForeground(NOTIFICATION_ID, getNotification()); 
    }

   public void toBackground(){ 
        stopForeground(true); 
   }   
    /**
     * Returns the {@link NotificationCompat} used as part of the foreground service.
     */
    private Notification getNotification() {
        Intent intent = new Intent(this, ForegroundService.class);  

        // The PendingIntent that leads to a call to onStartCommand() in this service.
        PendingIntent servicePendingIntent = PendingIntent.getService(this, 0, intent,
                PendingIntent.FLAG_UPDATE_CURRENT);

        // The PendingIntent to launch activity.
        PendingIntent activityPendingIntent = PendingIntent.getActivity(this, 0,
                new Intent(this, MainActivity.class), 0);

        NotificationCompat.Builder builder = new NotificationCompat.Builder(this)
                .addAction(R.drawable.shell_notification_icon, getString(R.string.launch_activity),
                        activityPendingIntent) 
                .setContentText(text)
                .setContentTitle(Utils.getLocationTitle(this))
                .setOngoing(true)
                .setPriority(Notification.PRIORITY_DEFAULT)
                .setSmallIcon(R.drawable.shell_notification_icon)
                .setTicker(text)
                .setDefaults(Notification.DEFAULT_LIGHTS)
                .setWhen(System.currentTimeMillis());

        // Set the Channel ID for Android O.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            builder.setChannelId(CHANNEL_ID); // Channel ID
        }

        return builder.build();
    }
//...
}