在我的应用中，我想获取纬度，经度和当前位置名称，并在数据库中传递此值。该应用程序在Tab中运行完美。但是在其他设备的情况下getLastKnownLocation()返回null。出于这个原因，我面临nullpointerexception。
private Location getLastKnownLocation() {
locationmanager = (LocationManager) getApplicationContext().getSystemService(LOCATION_SERVICE);
List<String> providers = locationmanager.getProviders(true);
Location bestLocation = null;
for (String provider : providers) {
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return null;
}
Location l = locationmanager.getLastKnownLocation(LocationManager.PASSIVE_PROVIDER);
if (l == null) {
continue;
}
if (bestLocation == null || l.getAccuracy() < bestLocation.getAccuracy()) {
// Found best last known location: %s", l);
bestLocation = l;
}
}
return bestLocation;
}
请帮我解决这个问题。我知道以前问过这个问题。但我尝试了大部分。我仍然在同一个地方面对nullpointerexception（在获取lat long值时）。
10-13 15：54：12.825 16095-16095 / com.example.ivdisplays.vehereapp E / AndroidRuntime：FATAL EXCEPTION：main 处理：com.example.ivdisplays.vehereapp，PID：16095 显示java.lang.NullPointerException 在com.example.ivdisplays.vehereapp.MainActivity $ 1.onClick（MainActivity.java:117） 在android.view.View.performClick（View.java:4463） 在android.view.View $ PerformClick.run（View.java:18792） 在android.os.Handler.handleCallback（Handler.java:808） 在android.os.Handler.dispatchMessage（Handler.java:103） 在android.os.Looper.loop（Looper.java:193） 在android.app.ActivityThread.main（ActivityThread.java:5344） at java.lang.reflect.Method.invokeNative（Native Method） 在java.lang.reflect.Method.invoke（Method.java:515） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:860） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:676） 在dalvik.system.NativeStart.main（本地方法）
public class MainActivity extends AppCompatActivity implements NetworkCallback,
LocationListener {
private EditText empIdTxt;
private EditText passwordTxt;
private TextView tv_lat;
private TextView tv_long;
private TextView tv_place;
private Button loginBtn;
private Button logoutBtn;
LocationManager locationmanager;
GPSTracker gps;
String cityName = "";
Context context;
static String loginDate;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
empIdTxt = (EditText) findViewById(R.id.et_loginId);
passwordTxt = (EditText) findViewById(R.id.et_loginPass);
loginBtn = (Button) findViewById(R.id.bt_login);
logoutBtn= (Button) findViewById(R.id.bt_logout);
empIdTxt.addTextChangedListener(new MyTextWatcher(empIdTxt));
passwordTxt.addTextChangedListener(new MyTextWatcher(passwordTxt));
empIdTxt.setText("vinay");
passwordTxt.setText("qwerty");
context=MainActivity.this;
final Location location = getLastKnownLocation();
if (location != null) {
onLocationChanged(location);
} else {
Toast.makeText(getApplicationContext(), "location not found", Toast.LENGTH_LONG).show();
System.out.println("Output of Location is:" + getLastKnownLocation());
}
loginDate = AlertDialogManager.todayDate();
loginBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (!validateEmpID()) {
return;
}
if (!validatePassword()) {
return;
}
LoginApi api = new LoginApi(context, (NetworkCallback) context);
System.out.println("Output of LoginAPI:" +"username" +empIdTxt.getText().toString()
+"password"+passwordTxt.getText().toString()+"Lat"+location.getLatitude()+"Long"+location.getLongitude()
+"Date"+loginDate+"Locality"+new GPSTracker(MainActivity.this).getLocality(location));
api.processLogin(empIdTxt.getText().toString(), passwordTxt.getText().toString(),
location.getLatitude()+"",location.getLongitude()+"",loginDate,
new GPSTracker(MainActivity.this).getLocality(location),"123456");
loginBtn.setVisibility(View.GONE);
logoutBtn.setVisibility(View.VISIBLE);
}
});
logoutBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
LogoutApi api = new LogoutApi(context, (NetworkCallback) context);
System.out.println("Output of LogoutAPI:" +"userid " +AppDelegate.getInstance().uid
+"Lat"+location.getLatitude()+"Long"+location.getLongitude()
+"Date"+AlertDialogManager.todayDate()+"Locality"+new GPSTracker(MainActivity.this).getLocality(location));
api.processLogout(AppDelegate.getInstance().uid,
location.getLatitude()+"",location.getLongitude()+"",AlertDialogManager.todayDate(),
new GPSTracker(MainActivity.this).getLocality(location),"123456","");
logoutBtn.setVisibility(View.GONE);
loginBtn.setVisibility(View.VISIBLE);
}
});
}
private Location getLastKnownLocation() {
locationmanager = (LocationManager) getApplicationContext().getSystemService(LOCATION_SERVICE);
List<String> providers = locationmanager.getProviders(true);
Location bestLocation = null;
for (String provider : providers) {
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return null;
}
Location l = locationmanager.getLastKnownLocation(provider);
if (l == null) {
continue;
}
if (bestLocation == null || l.getAccuracy() < bestLocation.getAccuracy()) {
// Found best last known location: %s", l);
bestLocation = l;
}
}
return bestLocation;
}
private void requestFocus(View view) {
if (view.requestFocus()) {
getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);
}
}
private boolean validateEmpID() {
if (empIdTxt.getText().toString().trim().isEmpty()) {
empIdTxt.setError(ErrorUtil.USERNAME_ERROR);
requestFocus(empIdTxt);
return false;
}
return true;
}
private boolean validatePassword() {
if (passwordTxt.getText().toString().trim().isEmpty()) {
passwordTxt.setError(ErrorUtil.PASSWORD_ERROR);
requestFocus(passwordTxt);
return false;
}
return true;
}
private class MyTextWatcher implements TextWatcher {
private View view;
private MyTextWatcher(View view) {
this.view = view;
}
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
public void afterTextChanged(Editable editable) {
switch (view.getId()) {
case R.id.et_loginId:
validateEmpID();
break;
case R.id.et_loginPass:
validatePassword();
break;
}
}
}
@Override
public void updateScreen(String data, String tag) {
if (tag.compareTo(ApiUtil.TAG_LOGIN) == 0) {
try {
System.out.println("Login Response"+data);
JSONObject mainObj = new JSONObject(data);
AppDelegate ctrl = AppDelegate.getInstance();
if (!mainObj.isNull("user_id")) {
ctrl.uid = mainObj.getString("user_id");
}
if (!mainObj.isNull("error")) {
Toast.makeText(MainActivity.this,"Login Fails",Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this,"Login Success",Toast.LENGTH_SHORT).show();
}
} catch (Exception e) {
Toast.makeText(MainActivity.this,"Seems there is an issue please try again later",Toast.LENGTH_SHORT).show();
}
}
if (tag.compareTo(ApiUtil.TAG_LOGOUT) == 0) {
try {
System.out.println("Logout Response"+data);
JSONObject mainObj = new JSONObject(data);
AppDelegate ctrl = AppDelegate.getInstance();
if (!mainObj.isNull("message")) {
Toast.makeText(MainActivity.this,"Logout Success",Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this,"Logout Fails",Toast.LENGTH_SHORT).show();
}
} catch (Exception e) {
Toast.makeText(MainActivity.this,"Seems there is an issue please try again later",Toast.LENGTH_SHORT).show();
}
}
}
@Override
public void onLocationChanged(Location location) {
double latitude,longitude;
tv_lat = (TextView) findViewById(R.id.tv_lat);
tv_long = (TextView) findViewById(R.id.tv_long);
tv_place = (TextView) findViewById(R.id.tv_place);
latitude=location.getLatitude();
longitude=location.getLongitude();
tv_lat.setText("Latitude : "+latitude);
tv_long.setText("Longitude : "+ longitude);
// create class object
gps = new GPSTracker(MainActivity.this);
// check if GPS enabled
if (gps.canGetLocation()) {
Geocoder geocoder = new Geocoder(MainActivity.this, Locale.getDefault());
List<Address> addresses;
try {
addresses = geocoder.getFromLocation(latitude,
longitude, 1);
System.out.println("Output of Address" + addresses);
cityName = addresses.get(0).getAddressLine(0);
System.out.println("Cityname is" + cityName);
tv_place.setText("Place : "+cityName);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else {
gps.showSettingsAlert();
}
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle) {
}
@Override
public void onProviderEnabled(String s) {
}
@Override
public void onProviderDisabled(String s) {
}
}
答案 0 :(得分：0)
我认为问题在于检查权限和&& !=操作数。处理它更仔细。
试试这个：
private Location getLastKnownLocation() {
locationmanager = (LocationManager) getApplicationContext().getSystemService(LOCATION_SERVICE);
boolean permissionsActivated = canAll();
if (!permissionsActivated)
return null;
List<String> providers = locationmanager.getProviders(true);
Location bestLocation = null;
for (String provider : providers) {
Location l = lm.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);// this may lead to 'null' value if not permissions
if (l == null) {
continue;
}
if (bestLocation == null || l.getAccuracy() < bestLocation.getAccuracy()) {
// Found best last known location: %s", l);
bestLocation = l;
}
}
return bestLocation;
}
private boolean canAll() {
// TODO Auto-generated method stub
return (canAccessLocation() && canCoarseLocation());
}
private boolean canAccessLocation() {
return hasPermission(android.Manifest.permission.ACCESS_FINE_LOCATION);
}
private boolean canCoarseLocation() {
return hasPermission(android.Manifest.permission.ACCESS_COARSE_LOCATION);
}
@SuppressLint("NewApi")
private boolean hasPermission(String perm) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
return (PackageManager.PERMISSION_GRANTED == checkSelfPermission(perm));
} else {
return true;
}
}
不要忘记：
如果应用程序未检测到任何位置， getLastKnownLocation可能会返回空值。
答案 1 :(得分：0)
您可以使用GoogleApiClient's fused location provider获取位置信息。您需要在gradle文件中添加依赖项。即
compile 'com.google.android.gms:play-services-location:9.6.1'
在清单
中添加fine_location权限
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
Dangerous Permission您需要在运行时询问this.
等权限代码段
public class DashboardActivity extends AppCompatActivity implements
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener,
LocationListener,
ResultCallback<LocationSettingsResult> {
private GoogleApiClient googleApiClient;
private GoogleApiAvailability apiAvailability;
private static final long MIN_TIME_BW_UPDATES = 10000;
private static final long FAST_TIME_BW_UPDATES = 3000;
private final static int REQUEST_CHECK_SETTINGS = 100;
private static final long EXPIRATION_DURATION = 3600000;
protected LocationRequest mLocationRequest;
protected LocationSettingsRequest mLocationSettingsRequest;
private Location location;
private LatLng latLng = new LatLng(0, 0);
private double latitude;
private double longitude;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dashboard);
init();
}
private void init() {
apiAvailability = GoogleApiAvailability.getInstance();
if (googleApiAvaibility()) {
buildGoogleApiClient();
displayLocation();
}
}
protected void createLocationRequest() {
mLocationRequest = LocationRequest.create();
mLocationRequest.setInterval(MIN_TIME_BW_UPDATES);
mLocationRequest.setFastestInterval(FAST_TIME_BW_UPDATES);
mLocationRequest.setSmallestDisplacement(10);
mLocationRequest.setExpirationDuration(EXPIRATION_DURATION);
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
LocationSettingsRequest.Builder builder = new LocationSettingsRequest.Builder();
builder.addLocationRequest(mLocationRequest);
builder.setAlwaysShow(true);
mLocationSettingsRequest = builder.build();
}
protected synchronized void buildGoogleApiClient() {
googleApiClient = new GoogleApiClient.Builder(getApplicationContext())
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
}
private boolean googleApiAvaibility() {
int resultCode = apiAvailability.isGooglePlayServicesAvailable(this);
switch (resultCode) {
case ConnectionResult.SUCCESS:
return true;
case ConnectionResult.API_UNAVAILABLE:
Dialog dialog = apiAvailability.getErrorDialog(this, ConnectionResult.API_UNAVAILABLE, 200,
new DialogInterface.OnCancelListener() {
@Override
public void onCancel(DialogInterface dialog) {
//finish();
}
});
dialog.show();
break;
case ConnectionResult.SERVICE_MISSING:
Dialog dialog1 = apiAvailability.getErrorDialog(this, ConnectionResult.SERVICE_MISSING, 201,
new DialogInterface.OnCancelListener() {
@Override
public void onCancel(DialogInterface dialog) {
//finish();
}
});
dialog1.show();
break;
}
return false;
}
@Override
public void onLocationChanged(Location location) {
latLng = new LatLng(location.getLatitude(), location.getLongitude());
//here you will get new latitude and longitude if location is changed
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
switch (requestCode) {
case REQUEST_CHECK_SETTINGS:
switch (resultCode) {
case Activity.RESULT_OK:
displayLocation();
break;
case Activity.RESULT_CANCELED:
//finish();
Toast.makeText(getActivity(), "Please enable location. Otherwise you can not use this application", Toast.LENGTH_LONG).show();
break;
}
break;
default:
break;
}
}
@Override
public void onConnected(@Nullable Bundle bundle) {
createLocationRequest();
checkLocationSettings();
}
@Override
public void onConnectionSuspended(int i) {
googleApiClient.connect();
}
@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
googleApiClient.connect();
}
@Override
public void onResult(@NonNull LocationSettingsResult result) {
Status status = result.getStatus();
switch (status.getStatusCode()) {
case LocationSettingsStatusCodes.SUCCESS:
displayLocation();
break;
case LocationSettingsStatusCodes.RESOLUTION_REQUIRED:
try {
status.startResolutionForResult(this, REQUEST_CHECK_SETTINGS);
} catch (IntentSender.SendIntentException e) {
Log.e("Exception", e.toString());
}
break;
case LocationSettingsStatusCodes.SETTINGS_CHANGE_UNAVAILABLE:
//showDialog(this,"You have choose never for Location!");
break;
default:
break;
}
}
protected void checkLocationSettings() {
PendingResult<LocationSettingsResult> result = LocationServices.SettingsApi.
checkLocationSettings(googleApiClient, mLocationSettingsRequest);
result.setResultCallback(this);
}
private void displayLocation() {
if (ActivityCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 250);
} else {
location = LocationServices.FusedLocationApi.getLastLocation(googleApiClient);
if (location != null) {
latLng = new LatLng(location.getLatitude(), location.getLongitude());
latitude = location.getLatitude();
longitude = location.getLongitude();
//print latitude longitude here
} else {
if (googleApiAvaibility()) {
buildGoogleApiClient();
googleApiClient.connect();
if (googleApiClient.isConnected()) {
LocationServices.FusedLocationApi.requestLocationUpdates(googleApiClient, mLocationRequest, this);
}
}
}
}
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
if (permissions[0].equals(Manifest.permission.ACCESS_FINE_LOCATION)) {
if (location != null) {
displayLocation();
} else {
//googleApiClient.connect();
if (googleApiAvaibility()) {
buildGoogleApiClient();
googleApiClient.connect();
}
}
}
}
}
}
您还可以查看此sample