问题
I am not sure were I went wrong, getting a nullPointerException on using googlemap.setMyLocationEnabled(true) in Google Map v2 example.
MainActivity.java File:
package com.example.locationgooglemapsv2;
import java.io.IOException;
import java.util.List;
import android.content.Context;
import android.location.Address;
import android.location.Criteria;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.view.Menu;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.GoogleMap.OnMapClickListener;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
public class MainActivity extends FragmentActivity implements LocationListener {
GoogleMap googleMap;
MarkerOptions markerOptions;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Getting reference to the SupportMapFragment of activity_main.xml
SupportMapFragment fm = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
// Getting GoogleMap object from the fragment
googleMap = fm.getMap();
// Enabling MyLocation Layer of Google Map
googleMap.setMyLocationEnabled(true);
/*======== MAP TYPE ==========*/
googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
RadioGroup rgViews = (RadioGroup) findViewById(R.id.rg_views);
rgViews.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
// TODO Auto-generated method stub
switch(checkedId){
case R.id.normal: googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
break;
case R.id.satellite:googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
break;
case R.id.terrain: googleMap.setMapType(GoogleMap.MAP_TYPE_TERRAIN);
break;
}
}
});
/*======== MARKER AND ONCLICK ==========*/
googleMap.setOnMapClickListener(new OnMapClickListener() {
@Override
public void onMapClick(LatLng latlng) {
// Creating a marker
MarkerOptions markerOption = new MarkerOptions();
// Setting the position for the marker
markerOption.position(latlng);
// Setting the title for the marker.
// This will be displayed on taping the marker
//markerOption.title(latlng.latitude + " : " + latlng.longitude);
// Clears the previously touched position
googleMap.clear();
// Animating to the touched position
googleMap.animateCamera(CameraUpdateFactory.newLatLng(latlng));
// Placing a marker on the touched position
googleMap.addMarker(markerOption);
// Adding Marker on the touched location with address
new ReverseGeocodingTask(getBaseContext()).execute(latlng);
}
});
/*======== LOCATION ==========*/
// Getting LocationManager object from System Service LOCATION_SERVICE
LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
// Creating a criteria object to retrieve provider
Criteria criteria = new Criteria();
// Getting the name of the best provider
String provider = locationManager.getBestProvider(criteria, true);
// Getting Current Location
Location location = locationManager.getLastKnownLocation(provider);
if(location!=null){
onLocationChanged(location);
}
locationManager.requestLocationUpdates(provider, 20000, 0, this);
}
@Override
public void onLocationChanged(Location location) {
// TODO Auto-generated method stub
double lat = location.getLatitude();
double lng = location.getLongitude();
//--maps
LatLng latlng = new LatLng(lat, lng);
googleMap.moveCamera(CameraUpdateFactory.newLatLng(latlng));
googleMap.animateCamera(CameraUpdateFactory.zoomTo(10));
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
/*======== REVERSE GEO CODING ==========*/
class ReverseGeocodingTask extends AsyncTask<LatLng, Void, String>{
Context mContext;
public ReverseGeocodingTask( Context con) {
super();
this.mContext = con;
}
@Override
protected String doInBackground(LatLng... params) {
// TODO Auto-generated method stub
Geocoder geocoder = new Geocoder(mContext);
double lat = params[0].latitude;
double lng = params[0].longitude;
List<Address> addresses = null;
String actualAdress = "";
try {
addresses = geocoder.getFromLocation(lat, lng, 1);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if(addresses != null && addresses.size() > 0){
Address address = addresses.get(0);
actualAdress = String.format("%s, %s, %s", address.getMaxAddressLineIndex() > 0 ? address.getAddressLine(0) : "",
address.getLocality(), address.getCountryName());
}
return actualAdress;
}
@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
// Setting the title for the marker.
// This will be displayed on taping the marker
markerOptions.title(result);
// Placing a marker on the touched position
googleMap.addMarker(markerOptions);
}
}
}
Manifest File:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.locationgooglemapsv2"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="16" />
<permission
android:name="com.example.locationgooglemapsv2.permission.MAPS_RECIEVE"
android:protectionLevel="signature" >
</permission>
<uses-permission android:name="com.example.locationgooglemapsv2.permission.MAPS_RECIEVE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" />
<uses-feature
android:glEsVersion="0x00020000"
android:required="true"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.locationgooglemapsv2.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="API_KEY" />
</application>
</manifest>
Error Log:
01-11 21:11:56.282: E/AndroidRuntime(327): FATAL EXCEPTION: main
01-11 21:11:56.282: E/AndroidRuntime(327): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.locationgooglemapsv2/com.example.locationgooglemapsv2.MainActivity}: java.lang.NullPointerException
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.os.Handler.dispatchMessage(Handler.java:99)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.os.Looper.loop(Looper.java:123)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.ActivityThread.main(ActivityThread.java:4627)
01-11 21:11:56.282: E/AndroidRuntime(327): at java.lang.reflect.Method.invokeNative(Native Method)
01-11 21:11:56.282: E/AndroidRuntime(327): at java.lang.reflect.Method.invoke(Method.java:521)
01-11 21:11:56.282: E/AndroidRuntime(327): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-11 21:11:56.282: E/AndroidRuntime(327): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-11 21:11:56.282: E/AndroidRuntime(327): at dalvik.system.NativeStart.main(Native Method)
01-11 21:11:56.282: E/AndroidRuntime(327): Caused by: java.lang.NullPointerException
01-11 21:11:56.282: E/AndroidRuntime(327): at com.example.locationgooglemapsv2.MainActivity.onCreate(MainActivity.java:46)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-11 21:11:56.282: E/AndroidRuntime(327): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-11 21:11:56.282: E/AndroidRuntime(327): ... 11 more
BTW the source is a good example for those who are trying to play with google map v2 and is well commented.
Any help regarding the error is appreciated.
Thanks in advance.
回答1:
getmap() is returning null. That means the map is not ready. Either because the fragment is not ready or your are running on a device without Google Play services available. See getMap for more info.
回答2:
I was getting something simular due to the Google Play Services API being missing from the device. If you use:
GooglePlayServicesUtil.isGooglePlayServicesAvailable(Context)
It should return ConnectionResult.SUCCESS if available. if it returns
ConnectionResult.SERVICE_MISSING
ConnectionResult.SERVICE_VERSION_UPDATE_REQUIRED
ConnectionResult.SERVICE_DISABLED
you can prompt the user to download it using
GooglePlayServicesUtil.getErrorDialog()
来源：https://stackoverflow.com/questions/14282045/google-maps-v2-error-on-use-of-setmylocationenabled