Question

我正在尝试在后台运行一项服务，该服务会发送手机位置的短信息。在服务中我使用了一个Timer。发送消息的代码运行正常但是当我尝试将代码放入以查找用户位置时，我总是遇到错误。

我试图调用一个新线程并使用了一个looper但现在我得到一个nullpointerexception，指向这两行代码：

sendSmsMessage();

并且在此方法中：

if (coordinates.equals(null) || coordinates.equals("") || coordinates == null || coordinates == ""){
        coordinates = "Could Not Receive Location";
    }

所以，我问的问题是为什么会出现这个错误？如果你能帮助我，我将不胜感激。如果我只是忽略了一些非常简单的事情，请指出来。谢谢！

以下是代码：

    public class MessageService extends Service{
int counter = 0;
private Timer timer = new Timer();
public String textTime, phoneNumber;
public int updateInterval;
int lat, lng;
String coordinates, latitude, longitude;
LocationManager locationManager;

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

@Override
public int onStartCommand(Intent intent, int flags, int startId){
    //receives the intent extras from the calling intent
    textTime = intent.getStringExtra("textTime");
    phoneNumber = intent.getStringExtra("phone");

    phoneNumber = "5556";

    //the following if statement has to do with transferring the string textTime into a number that can be used
    if (textTime.equals("15 Minutes")) {
        updateInterval = (15 * (60000));
    }else if (textTime.equals("30 Minutes")) {
        updateInterval = (30 * (60000));
    }else if (textTime.equals("1 Hour")){
        updateInterval = (60 * (60000));
    }else {
        updateInterval = (15 * (60000));
    }

    locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

    new Thread(){
        public void run(){
            Looper.prepare();
            // Define a listener that responds to location updates
            LocationListener locationListener = new LocationListener() {
                public void onLocationChanged(Location location) {
                  // Called when a new location is found by the network location provider.
                  //makeUseOfNewLocation(location);
                    lat = (int) (location.getLatitude() * 1E6);
                    lng = (int) (location.getLongitude() * 1E6);

                    latitude = Integer.toString(lat);
                    longitude = Integer.toString(lng);

                    coordinates = "Coordinates: " + latitude + ", " + longitude + ". Latitude: " + latitude + " Longitude: " + longitude + ". Respond 'END' to stop texts."; 
                }

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

                public void onProviderEnabled(String provider) {}

                public void onProviderDisabled(String provider) {}
              };

              Looper.loop();

              if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)){
                    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
              }else{
                    locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
              }

        }
    }.start();


    //the following method should use a timer to send a sms message in a timed interval. It also should implement using a different thread
    doSomethingRepeatedly();

    return START_STICKY;

}

public void doSomethingRepeatedly(){
    timer.scheduleAtFixedRate(new TimerTask() {
        public void run() {
            //the following code should be what is done repeatedly
            //Log.d("MessageService", String.valueOf(++counter));

            sendSmsMessage();
        }
    }, 0, updateInterval);
}

//the following code handles sending the text message
public void sendSmsMessage(){
    SmsManager sms = SmsManager.getDefault();
    if (coordinates.equals(null) || coordinates.equals("") || coordinates == null || coordinates == ""){
        coordinates = "Could Not Receive Location";
    }

    sms.sendTextMessage(phoneNumber, null, "test" , null, null);

}

public void onDestroy() {
    super.onDestroy();

    if (timer != null) {
        timer.cancel();
    }
}




}//end of service

这是logcat输出：

    10-19 20:23:28.096: E/AndroidRuntime(944): FATAL EXCEPTION: Timer-0
10-19 20:23:28.096: E/AndroidRuntime(944): java.lang.NullPointerException
10-19 20:23:28.096: E/AndroidRuntime(944):  at com.app.MessageService.sendSmsMessage(MessageService.java:113)
10-19 20:23:28.096: E/AndroidRuntime(944):  at com.app.MessageService$2.run(MessageService.java:105)
10-19 20:23:28.096: E/AndroidRuntime(944):  at      java.util.Timer$TimerImpl.run(Timer.java:284)

Answer 1

您需要替换

coordinates.equals(null)

带

coordinates == null

由于第一个永远不会评估为true，因此每次NullPointerException()为coordinates时，它都会抛出null。

Answer 2

如果您的coordinates为空，那么第一个条件oordinates.equals(null)将导致NullPointerException。

另外，我还有一个观察结果。比较coordinates == ""没有用，因为你已经以正确的方式使用它，即coordinates.equals（“”）。

从

更改if

if (coordinates.equals(null) || coordinates.equals("") || 
                                    coordinates == null || coordinates == ""){
    coordinates = "Could Not Receive Location";
}

到

if (coordinates == null || coordinates.equals("")){
    coordinates = "Could Not Receive Location";
}

空指针异常导致在尝试运行多个线程时强制关闭

2 个答案: