Question

我正在尝试使用Android hive的教程来了解如何跟踪用户的位置并向他们展示附近的位置。我想通知用户有关位置更改并将其重定向到应用程序的第一个屏幕。我试过调用包含来自onlocationchanged方法的通知代码的类，但它在pendingintent.getactivity（）中显示空指针异常。我在清单文件中添加了所有权限，这里是代码：

GPSTracker.java：

这是包含onlocationchanged的文件，我试图调用shownotif（）。公共类GPSTracker extends Service实现LocationListener {

private final Context mContext;
Notif n = new Notif();
// flag for GPS status
boolean isGPSEnabled = false;

// flag for network status
boolean isNetworkEnabled = false;

// flag for GPS status
boolean canGetLocation = false;

Location location = null; // location
double latitude; // latitude
double longitude; // longitude

// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 0;

// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 0;

// Declaring a Location Manager
protected LocationManager locationManager;

public GPSTracker(Context context) {
    this.mContext = context;
    getLocation();
}

public Location getLocation() {
    try {
        locationManager = (LocationManager) mContext
                .getSystemService(LOCATION_SERVICE);

        // getting GPS status
        isGPSEnabled = locationManager
                .isProviderEnabled(LocationManager.GPS_PROVIDER);

        // getting network status
        isNetworkEnabled = locationManager
                .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

        if (!isGPSEnabled && !isNetworkEnabled) {
            // no network provider is enabled
        } else {
            this.canGetLocation = true;
            if (isNetworkEnabled) {
                locationManager.requestLocationUpdates(
                        LocationManager.NETWORK_PROVIDER,
                        MIN_TIME_BW_UPDATES,
                        MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                Log.d("Network", "Network Enabled");
                if (locationManager != null) {
                    location = locationManager
                            .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                    if (location != null) {
                        latitude = location.getLatitude();
                        longitude = location.getLongitude();
                    }
                }
            }
            // if GPS Enabled get lat/long using GPS Services
            if (isGPSEnabled) {
                if (location == null) {
                    locationManager.requestLocationUpdates(
                            LocationManager.GPS_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("GPS", "GPS Enabled");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
            }
        }
        Toast.makeText(getApplicationContext(), "Location changed",Toast.LENGTH_SHORT).show();

    } catch (Exception e) {
        e.printStackTrace();
    }

    return location;
}

/**
 * Stop using GPS listener Calling this function will stop using GPS in your
 * app
 * */
public void stopUsingGPS() {
    if (locationManager != null) {
        locationManager.removeUpdates(GPSTracker.this);
    }
}

/**
 * Function to get latitude
 * */
public double getLatitude() {
    if (location != null) {
        latitude = location.getLatitude();
    }

    // return latitude
    return latitude;
}

/**
 * Function to get longitude
 * */
public double getLongitude() {
    if (location != null) {
        longitude = location.getLongitude();
    }

    // return longitude
    return longitude;
}

/**
 * Function to check GPS/wifi enabled
 *
 * @return boolean
 * */
public boolean canGetLocation() {
    return this.canGetLocation;
}

/**
 * Function to show settings alert dialog On pressing Settings button will
 * lauch Settings Options
 * */
public void showSettingsAlert() {
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);

    // Setting Dialog Title
    alertDialog.setTitle("GPS is settings");

    // Setting Dialog Message
    alertDialog
            .setMessage("GPS is not enabled. Do you want to go to settings menu?");

    // On pressing Settings button
    alertDialog.setPositiveButton("Settings",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    Intent intent = new Intent(
                            Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                    mContext.startActivity(intent);
                }
            });

    // on pressing cancel button
    alertDialog.setNegativeButton("Cancel",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    dialog.cancel();
                }
            });

    // Showing Alert Message
    alertDialog.show();
}

@Override
public void onLocationChanged(Location location) {
        //notification
    if(location!=null) {
        n.shownotif(this);
    }

}

@Override
public void onProviderDisabled(String provider) {
}

@Override
public void onProviderEnabled(String provider) {
}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}

@Override
public IBinder onBind(Intent arg0) {
    return null;
}

}

这是notif.java

public class Notif {
void shownotif(Context context)
{

    PendingIntent pi = PendingIntent.getActivity(context, 0, new Intent(context, MainActivity.class), 0);
    Notification noti = new NotificationCompat.Builder(context)
            .setContentTitle("Notification")
            .setContentText("There are new places to visit")
            .setSmallIcon(android.R.drawable.stat_sys_warning)
            .setContentIntent(pi)
            .setDefaults(Notification.DEFAULT_SOUND)
            .setDefaults(Notification.DEFAULT_VIBRATE)
            .setWhen(System.currentTimeMillis())
            .setAutoCancel(true)
            .build();
    NotificationManager mgr = (NotificationManager)context.getSystemService(Context.NOTIFICATION_SERVICE);
    mgr.notify(0,noti);
}

}

这是mainactivity.java oncreate方法

    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    cd = new ConnectionDetector(getApplicationContext());

    // Check if Internet present
    isInternetPresent = cd.isConnectingToInternet();
    if (!isInternetPresent) {
        // Internet Connection is not present
        alert.showAlertDialog(MainActivity.this, "Internet Connection Error",
                "Please connect to working Internet connection", false);
        // stop executing code by return
        return;
    }

    // creating GPS Class object
    gps = new GPSTracker(this);

    // check if GPS location can get
    if (gps.canGetLocation()) {
        Log.d("Your Location", "latitude:" + gps.getLatitude() + ", longitude: " + gps.getLongitude());
    } else {
        // Can't get user's current location
        alert.showAlertDialog(MainActivity.this, "GPS Status",
                "Couldn't get location information. Please enable GPS",
                false);
        // stop executing code by return
        return;
    }

    // Getting listview
    lv = (ListView) findViewById(R.id.list);

    // button show on map
    btnShowOnMap = (Button) findViewById(R.id.btn_show_map);

    // calling background Async task to load Google Places
    // After getting places from Google all the data is shown in listview
    new LoadPlaces().execute();

    /** Button click event for shown on map */
    btnShowOnMap.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            Intent i = new Intent(getApplicationContext(),
                    PlacesMapActivity.class);
            // Sending user current geo location
            i.putExtra("user_latitude", Double.toString(gps.getLatitude()));
            i.putExtra("user_longitude", Double.toString(gps.getLongitude()));

            // passing near places to map activity
            i.putExtra("near_places", nearPlaces);
            // staring activity
            startActivity(i);
        }
    });


    /**
     * ListItem click event
     * On selecting a listitem SinglePlaceActivity is launched
     * */
    lv.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
            // getting values from selected ListItem
            String reference = ((TextView) view.findViewById(R.id.reference)).getText().toString();

            // Starting new intent
            Intent in = new Intent(getApplicationContext(),
                    SinglePlaceActivity.class);

            // Sending place refrence id to single place activity
            // place refrence id used to get "Place full details"
            in.putExtra(KEY_REFERENCE, reference);
            startActivity(in);
        }
    });
}

Answer 1

你传递的是错误的背景。你可能想要这样做：

@Override
public void onLocationChanged(Location location) {
  //notification
  if(location!=null) {
      n.shownotif(mContext);
  }

}

Answer 2

我试过调用包含来自onlocationchanged方法的通知代码的类，但它在pendingintent.getactivity（）中显示空指针异常。

PendingIntent pi = PendingIntent.getActivity(context, 0, new Intent(context, MainActivity.class), 0);

因为我在上下文中得到null，所以在onLocationChanged .e.g中传递mContext

    @Override
public void onLocationChanged(Location location) {
        //notification
    if(location!=null) {
        n.shownotif(mContext);
    }

自动通知用户有关位置更新的信息

2 个答案: