locationManager =(LocationManager)this.getSystemService(Context.LOCATION_SERVICE);返回空指针异常 [英] locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE); return null pointer exception
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问题描述
Followind代码始终为位置管理器返回空Poiner异常.
Followind code always return null poiner exception for location manager.
我的GPSTracker班 私有最终上下文mContext;
My GPSTracker class private final Context mContext;
// flag for GPS status
boolean isGPSEnabled = false;
// flag for network status
boolean isNetworkEnabled = false;
// flag for GPS status
boolean canGetLocation = false;
Location location; // location
double latitude; // latitude
double longitude; // longitude
// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute
// Declaring a Location Manager
protected LocationManager locationManager;
//Location locManager = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
public GPSTracker(Context context) {
this.mContext = context;
getLocation();
}
public Location getLocation() {
try {
locationManager = (LocationManager) this.getSystemService(Context.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;
// First get location 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();
}
}
}
// 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 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;
}
/**
* 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) {
this.location = location;
}
@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;
}
我正尝试致电
if(gps.isGPSEnabled){
Toast.makeText(getBaseContext(),"GPS enabled",
Toast.LENGTH_SHORT).show();
baseurl = "http://my.careerfolio.net";
}
else{
gps.showSettingsAlert();
}
它总是显示设置警报，而不是吐司文本，有什么帮助吗?
it always display settings alert rather then toast text, any help?
我的日志.
06-20 02:54:06.336: W/System.err(909): java.lang.NullPointerException
06-20 02:54:06.416: W/System.err(909): at android.content.ContextWrapper.getSystemService(ContextWrapper.java:519)
06-20 02:54:06.416: W/System.err(909): at com.incv.mobile.freejscf.GPSTracker.getLocation(GPSTracker.java:50)
06-20 02:54:06.446: W/System.err(909): at com.incv.mobile.freejscf.GPSTracker.<init>(GPSTracker.java:44)
06-20 02:54:06.446: W/System.err(909): at com.incv.mobile.freejscf.MyApplication.<init>(MyApplication.java:34)
06-20 02:54:06.446: W/System.err(909): at java.lang.Class.newInstanceImpl(Native Method)
06-20 02:54:06.456: W/System.err(909): at java.lang.Class.newInstance(Class.java:1130)
06-20 02:54:06.486: W/System.err(909): at android.app.Instrumentation.newApplication(Instrumentation.java:990)
06-20 02:54:06.486: W/System.err(909): at android.app.Instrumentation.newApplication(Instrumentation.java:975)
06-20 02:54:06.486: W/System.err(909): at android.app.LoadedApk.makeApplication(LoadedApk.java:504)
06-20 02:54:06.486: W/System.err(909): at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4417)
06-20 02:54:06.486: W/System.err(909): at android.app.ActivityThread.access$1300(ActivityThread.java:141)
06-20 02:54:06.486: W/System.err(909): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
06-20 02:54:06.506: W/System.err(909): at android.os.Handler.dispatchMessage(Handler.java:99)
06-20 02:54:06.506: W/System.err(909): at android.os.Looper.loop(Looper.java:137)
06-20 02:54:06.516: W/System.err(909): at android.app.ActivityThread.main(ActivityThread.java:5103)
06-20 02:54:06.516: W/System.err(909): at java.lang.reflect.Method.invokeNative(Native Method)
06-20 02:54:06.516: W/System.err(909): at java.lang.reflect.Method.invoke(Method.java:525)
06-20 02:54:06.546: W/System.err(909): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
06-20 02:54:06.546: W/System.err(909): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
06-20 02:54:06.546: W/System.err(909): at dalvik.system.NativeStart.main(Native Method)
推荐答案
您正试图在Location类而不是activity context中获得位置管理器，因此将Location类实例this更改为活动的上下文
You are trying to getting location manager in Location class not in activity context.So change Location class instance this to activity's context mContext. so change this
locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
到
locationManager = (LocationManager) mContext.getSystemService(Context.LOCATION_SERVICE);
修改
如果要使用GPS获取位置，则需要添加ACCESS_FINE_LOCATION(其中同时包含ACCESS_FINE_LOCATION和ACCESS_COARSE_LOCATION).另外，如果您要获取基于网络的位置，则还需要添加INTERNET 权限.
Edit
If you are getting location using GPS you need to add ACCESS_FINE_LOCATION (Which includes both ACCESS_FINE_LOCATION and ACCESS_COARSE_LOCATION ). Also if you are getting network-based location then you need to add INTERNET permission too.
因此，打开您的AndroidManifest.xml文件并进行以下更改.
So,Open your AndroidManifest.xml file and do the following changes.
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
这篇关于locationManager =(LocationManager)this.getSystemService(Context.LOCATION_SERVICE);返回空指针异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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