您好我正在尝试使用GPS追踪器查找位置，然后按下保存按钮以便在sharedPrefernces中保存位置并添加警报？该应用程序运行，但当我按下保存按钮它崩溃和'抱歉意外....'消息出现..任何帮助将非常感激
public class GPSTracker extends Service implements LocationListener{
//distance to update in meters and millisec's
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10;
private static final long MIN_TIME_BW_UPDATES = 1000 * 60;
//GPS & network status
boolean isGPSEnabled = false;
boolean isNetworkEnabled = false;
boolean canGetLocation = false;
Location location;
double latitude;
double longitude;
//Declaring location Manager
protected LocationManager locationManager;
private Context mContext;
public GPSTracker (Context context) {
this.mContext = context;
getLocation();
}
public Location getLocation(){
try{
locationManager = (LocationManager) mContext.getSystemService(LOCATION_SERVICE);
//getting GPS & network status
isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if (!isGPSEnabled && !isNetworkEnabled){
//none enabled
}
else{
this.canGetLocation = true;
//first from network provider
if (isNetworkEnabled){
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, MIN_TIME_BW_UPDATES, MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("Network","Network");
if(locationManager !=null) {
location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
}
if(location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
//Then use GPS service
if (isGPSEnabled){
if(location == null) {
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,MIN_TIME_BW_UPDATES,MIN_DISTANCE_CHANGE_FOR_UPDATES,this);
Log.d("GPS Enabled", "GPS Enabled");
if(locationManager !=null){
location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location !=null){
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
}
}catch (Exception e){
e.printStackTrace();
}
return location;
}
// function to get latitude
public double getLatitude(){
if(location !=null){
latitude = location.getLatitude();
}
return latitude;
}
//function to get longitude
public double getLongitude(){
if(location !=null){
longitude = location.getLongitude();
}
return longitude;
}
//Alert message to turn on GPS
//check network provider
public boolean canGetLocation(){
return this.canGetLocation;
}
//settings alert box
public void showSettingsAlert(){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
alertDialog.setTitle("GPS is settings");
//dialog message
alertDialog.setMessage("GPS are 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();
}
});
alertDialog.show();
}
//停止gps监听器 public void stopUsingGPS（）{ if（locationManager！= null）{ locationManager.removeUpdates（GPSTracker.this）; } }
public class MainActivity extends Activity {
protected LocationManager locationManager;
double latitude =0;
double longitude =0;
private static final String POINT_LATITUDE_KEY = "POINT_LATITUDE_KEY";
private static final String POINT_LONGITUDE_KEY = "POINT_LONGITUDE_KEY";
private static final long POINT_RADIUS = 1000; // in Meters
private static final long PROX_ALERT_EXPIRATION = -1;
private static final String PROX_ALERT_INTENT = "com.example.Shared.ProximityAlert";
GPSTracker gps;
Location location;
private static final NumberFormat nf = new DecimalFormat("##.########");
private EditText latitudeEditText;
private EditText longitudeEditText;
private Button findCoordinatesButton;
private Button savePointButton;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
latitudeEditText = (EditText) findViewById(R.id.point_latitude);
longitudeEditText = (EditText) findViewById(R.id.point_longitude);
findCoordinatesButton = (Button) findViewById(R.id.find_coordinates_button);
savePointButton = (Button) findViewById(R.id.save_point_button);
findCoordinatesButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// create class object
gps = new GPSTracker(MainActivity.this);
// check if GPS enabled
if(gps.canGetLocation()){
double latitude = gps.getLatitude();
double longitude = gps.getLongitude();
Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
latitudeEditText.setText(nf.format(gps.getLatitude()));
longitudeEditText.setText(nf.format(gps.getLongitude()));
}else{
gps.showSettingsAlert();
}
}
});
savePointButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
saveCoordinatesInPreferences(((float)gps.getLatitude()),((float)gps.getLongitude()));
addProximityAlert(gps.getLatitude(), gps.getLongitude());
Toast.makeText(getApplicationContext(), "Alert Paced on - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
}
});
}
void addProximityAlert(double latitude, double longitude) {
Intent intent = new Intent(PROX_ALERT_INTENT);
PendingIntent proximityIntent = PendingIntent.getBroadcast(this, 0, intent, 0);
locationManager.addProximityAlert(latitude, longitude, POINT_RADIUS, PROX_ALERT_EXPIRATION,proximityIntent);
IntentFilter filter = new IntentFilter(PROX_ALERT_INTENT);
registerReceiver(new ProximityIntentReceiver(), filter);
Log.d("Alert", "Proximity Alert Added");
}
void saveCoordinatesInPreferences(float latitude, float longitude) {
SharedPreferences prefs = this.getSharedPreferences(getClass().getSimpleName(), Context.MODE_PRIVATE);
SharedPreferences.Editor prefsEditor = prefs.edit();
prefsEditor.putFloat(POINT_LATITUDE_KEY, latitude);
prefsEditor.putFloat(POINT_LONGITUDE_KEY, longitude);
prefsEditor.commit();
}
Location retrievelocationFromPreferences() {
SharedPreferences prefs = this.getSharedPreferences(getClass().getSimpleName(), Context.MODE_PRIVATE);
Location location = new Location("POINT_LOCATION");
location.setLatitude(prefs.getFloat(POINT_LATITUDE_KEY, 0));
location.setLongitude(prefs.getFloat(POINT_LONGITUDE_KEY, 0));
return location;
}
和出现的错误
09-25 17:44:35.712: E/AndroidRuntime(16340): FATAL EXCEPTION: main
09-25 17:44:35.712: E/AndroidRuntime(16340): java.lang.NullPointerException
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:146)
09-25 17:44:35.712: E/AndroidRuntime(16340): at com.project.shared2.MainActivity.retrievelocationFromPreferences(MainActivity.java:119)
09-25 17:44:35.712: E/AndroidRuntime(16340): at com.project.shared2.GPSTracker.onLocationChanged(GPSTracker.java:152)
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:227)
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.location.LocationManager$ListenerTransport.access$000(LocationManager.java:160)
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.location.LocationManager$ListenerTransport$1.handleMessage(LocationManager.java:176)
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.os.Handler.dispatchMessage(Handler.java:99)
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.os.Looper.loop(Looper.java:123)
09-25 17:44:35.712: E/AndroidRuntime(16340): at android.app.ActivityThread.main(ActivityThread.java:3691)
09-25 17:44:35.712: E/AndroidRuntime(16340): at java.lang.reflect.Method.invokeNative(Native Method)
09-25 17:44:35.712: E/AndroidRuntime(16340): at java.lang.reflect.Method.invoke(Method.java:507)
09-25 17:44:35.712: E/AndroidRuntime(16340): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
09-25 17:44:35.712: E/AndroidRuntime(16340): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
09-25 17:44:35.712: E/AndroidRuntime(16340): at dalvik.system.NativeStart.main(Native Method)