【发布时间】：2017-01-02 12:22:59
【问题描述】：
我已经在片段中实现了地图。我想要当前位置，所以我实现了返回位置的位置侦听器。我正在调用一个 api 来获取所有商家，所以我得到了商家列表。从该列表中，我得到了商家的纬度和经度。
当我第一次启动应用程序并转到家庭活动中的 SearchMerchant 片段时，其中添加了地图。我可以看到当前位置和标记，如果我回到另一个片段并再次来到 SearchMerchant 片段，当我尝试在 onLocationChanged 方法中检查网络连接时，我会得到空指针异常。
Process: com.kiranacustomerapp, PID: 9934 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
at com.kiranacustomerapp.helper.CommonUtils.isConnectedToInternet(CommonUtils.java:44) at com.kiranacustomerapp.Fragments.SearchMerchantFragment.onLocationChanged(SearchMerchantFragment.java:373)
at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:297)
CommonUtils 类：
public static boolean isConnectedToInternet(Context context) {
ConnectivityManager manager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
if ( manager != null ) {
NetworkInfo[] info = manager.getAllNetworkInfo();
if ( info != null ) {
for(int i=0;i<info.length;i++) {
if ( info[i].getState() == NetworkInfo.State.CONNECTED) {
return true;
}
}
}
}
return false;
}
搜索地图片段：
public class SearchMerchantFragment extends Fragment implements GetSearchedMerchantsAsyncTask.GetSearchedMerchantsCallBack,OnMapReadyCallback , GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener{
// TODO: Rename parameter arguments, choose names that match
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// getLocation();
initializeLocationManager();
requestLocation();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_search_merchant, container, false);
setUpUI(view);
return view;
}
public void setUpUI(View view) {
setUpMapIfNeeded();
}
@Override
public void doPostExecute(ArrayList<Merchants> merchantsArrayList) {
merchantsList.clear();
merchantsList.addAll(merchantsArrayList);
merchantsAdapter.notifyDataSetChanged();
}
//get searched merchants
public void accessMerchants() {
if (CommonUtils.isConnectedToInternet(getContext())) {
new GetSearchedMerchantsAsyncTask(getActivity(), SearchMerchantFragment.this).execute(access_token, sessionUserId,String.valueOf(mLastLocation.getLatitude()),String.valueOf(mLastLocation.getLongitude()));
} else {
showAlert(String.valueOf(R.string.check_network));
}
}
private void setUpMapIfNeeded() {
if (mGoogleMap == null) {
mapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map_fragment);
mapFragment.getMapAsync(this);
// getLocation();
}
}
//setup map
@Override
public void onMapReady(GoogleMap googleMap) {
mGoogleMap = googleMap;
buildGoogleApiClient();
mGoogleApiClient.connect();
}
protected synchronized void buildGoogleApiClient() {
// Toast.makeText(getActivity(),"buildGoogleApiClient",Toast.LENGTH_SHORT).show();
mGoogleApiClient = new GoogleApiClient.Builder(getActivity())
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
}
@Override
public void onConnected(Bundle bundle) {
// Toast.makeText(getActivity(),"onConnected",Toast.LENGTH_SHORT).show();
}
@Override
public void onConnectionSuspended(int i) {
// Toast.makeText(getActivity(),"onConnectionSuspended",Toast.LENGTH_SHORT).show();
}
@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
// Toast.makeText(getActivity(),"onConnectionFailed",Toast.LENGTH_SHORT).show();
}
private class LocationListener implements android.location.LocationListener {
private static final String TAG = "GPS";
public LocationListener(String provider) {
Log.e(TAG, "LocationListener " + provider);
mLastLocation = new Location(provider);
}
@Override
public void onLocationChanged(Location location) {
Log.e(TAG, "onLocationChanged: " + location);
mLastLocation.set(location);
try {
if (mLastLocation != null) {
//place marker at current position
// mGoogleMap.clear();
mLatLang = new LatLng(mLastLocation.getLatitude(),mLastLocation.getLongitude());
accessMerchants();
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(mLatLang);
markerOptions.title(getString(R.string.position));
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE));
mMarker = mGoogleMap.addMarker(markerOptions);
CameraPosition cameraPosition = new CameraPosition.Builder().target(mLatLang).zoom(14).build();
mGoogleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
mLocationRequest = new LocationRequest();
mLocationRequest.setInterval(5000); //5 seconds
mLocationRequest.setFastestInterval(3000); //3 seconds
mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
mGoogleMap.setMyLocationEnabled(true);
mGoogleMap.getUiSettings().setZoomControlsEnabled(true);
mGoogleMap.getUiSettings().setAllGesturesEnabled(true);
for (Merchants merchants : merchantsList) {
LatLng latLng = new LatLng(merchants.getLatitude(), merchants.getLongitude());
MarkerOptions marker = new MarkerOptions().position(latLng).icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED)).title(merchants.getKirana_name());
Marker m = mGoogleMap.addMarker(marker);
markers.add(m);
}
}
} catch (SecurityException e) {
}
}
@Override
public void onProviderDisabled(String provider) {
Log.e(TAG, "onProviderDisabled: " + provider);
}
@Override
public void onProviderEnabled(String provider) {
Log.e(TAG, "onProviderEnabled: " + provider);
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
Log.e(TAG, "onStatusChanged: " + provider);
}
}
LocationListener[] mLocationListeners = new LocationListener[]{
new LocationListener(LocationManager.GPS_PROVIDER),
new LocationListener(LocationManager.NETWORK_PROVIDER)
};
private void initializeLocationManager() {
if (mLocationManager == null) {
mLocationManager = (LocationManager)getActivity().getSystemService(Context.LOCATION_SERVICE);
}
}
public void requestLocation() {
try {
mLocationManager.requestLocationUpdates(
LocationManager.NETWORK_PROVIDER, 0,0,
mLocationListeners[1]);
} catch (java.lang.SecurityException ex) {
} catch (IllegalArgumentException ex) {
}
try {
mLocationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,0,0,
mLocationListeners[0]);
} catch (java.lang.SecurityException ex) {
} catch (IllegalArgumentException ex) {
}
}
}
我想获取一次位置并调用异步任务来获取商家列表。获得位置后，我想停止获取位置，现在当我在 onLocationChange 方法中调用异步任务时，它会在位置更改后立即开始调用异步任务。所以经常发生。
这里出了什么问题？请帮忙，谢谢..
【问题讨论】：
标签： java android google-maps android-fragments location