[英]Null Pointer Exception causing force close while trying to run multiple threads
我正在嘗試在后台運行一項服務,該服務發送手機位置的短信。 在服務中,我使用計時器。 發送消息的代碼可以正確運行,但是當我嘗試將代碼放入以查找用戶位置時,總是會遇到錯誤。
我試圖調用一個新線程並使用了循環程序,但是現在我得到了一個nullpointerexception,它指向這兩行代碼:
sendSmsMessage();
並在此方法中:
if (coordinates.equals(null) || coordinates.equals("") || coordinates == null || coordinates == ""){
coordinates = "Could Not Receive Location";
}
因此,我要問的問題是為什么會發生此錯誤? 如果您能幫助我,將不勝感激。 如果我只是忽略一些非常簡單的內容,請指出。 謝謝!
這是代碼:
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
這是logcat的輸出:
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)
您需要更換
coordinates.equals(null)
同
coordinates == null
由於第一個永遠不會取值為true
,因此每次coordinates
為null
時,它將拋出NullPointerException()
。
如果coordinates
為null,則第一個條件oordinates.equals(null)
將導致NullPointerException
。
另外,我還有另外一個觀察。 比較coordinates == ""
是沒有用的,因為您已經以正確的方式使用它了,即坐標.equals(“”)。
if
從更改
if (coordinates.equals(null) || coordinates.equals("") ||
coordinates == null || coordinates == ""){
coordinates = "Could Not Receive Location";
}
至
if (coordinates == null || coordinates.equals("")){
coordinates = "Could Not Receive Location";
}
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