我正在开发一个带有2个选项卡的应用程序，每个选项卡都会加载其片段。第一个是ListFragment（没关系），第二个应该加载一个地图，但是当我试图将Google Map插入到这个Fragment中时，它会崩溃应用程序并显示错误：
06-11 18:11:52.973 32676-32676/br.com.toyansk.swipeabletabs E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: br.com.toyansk.swipeabletabs, PID: 32676
java.lang.NullPointerException
at br.com.toyansk.swipeabletabs.MapaFragment$HttpGetTask.onPostExecute(MapaFragment.java:100)
at br.com.toyansk.swipeabletabs.MapaFragment$HttpGetTask.onPostExecute(MapaFragment.java:69)
at android.os.AsyncTask.finish(AsyncTask.java:632)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
06-11 18:11:52.980 1037-3188/? W/ActivityManager﹕ Force finishing activity br.com.toyansk.swipeabletabs/.MainActivity
MainActivity.java是：
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
List<Fragment> mFragments;
// Tab titles
private String[] tabs = { "Lista", "Mapa" };
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initilization
viewPager = (ViewPager) findViewById(R.id.pager);
actionBar = getActionBar();
mAdapter = new TabsPagerAdapter(getSupportFragmentManager(), mFragments);
//mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
mFragments = new ArrayList<Fragment>();
mFragments.add(new List_Fragment());
viewPager.setAdapter(mAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
final int[] ICON = new int[] {
R.drawable.ic1,
R.drawable.ic2
};
// Adding Tabs
for (int i=0; i < tabs.length; i++) {
actionBar.addTab(actionBar.newTab()
.setIcon(getResources().getDrawable(ICON[i]))
.setTabListener(this));
}
/**
* on swiping the viewpager make respective tab selected
* */
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// on tab selected
// show respected fragment view
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
}
MapaFragment.java应该加载地图，它还具有使用JSON数据在地图上插入标记的功能，如下所示：
public class MapaFragment extends Fragment {
Context mContext;
private GoogleMap mMap;
private Location location;
private final static String URL = "api that returns maps data in JSON";
public static final String TAG = "MapaFragment";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_mapa, container, false);
new HttpGetTask().execute(URL);
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mContext = activity;
}
private class HttpGetTask extends AsyncTask<String, Void, List<PDVRec>> {
AndroidHttpClient mClient = AndroidHttpClient.newInstance("");
@Override
protected List<PDVRec> doInBackground(String... params) {
HttpGet request = new HttpGet(params[0]);
JSONResponseHandler responseHandler = new JSONResponseHandler();
try {
// Get data in JSON format
return mClient.execute(request, responseHandler);
} catch (ClientProtocolException e) {
Log.i(TAG, "ClientProtocolException");
} catch (IOException e) {
Log.i(TAG, "IOException");
}
return null;
}
@Override
protected void onPostExecute(List<PDVRec> result) {
// Get Map Object
mMap = ((SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
if (null != mMap) {
// Add a marker for every earthquake
for (PDVRec rec : result) {
// Add a new marker for this earthquake
mMap.addMarker(new MarkerOptions()
// Set the Marker's position
.position(new LatLng(rec.getLat(), rec.getLng()))
// Set the title of the Marker's information window
.title(String.valueOf(rec.getNome_PDV()))
// Set the icon for the Marker
.icon(BitmapDescriptorFactory.fromResource(R.drawable.currentlocation_icon)));
}
LocationManager locationManager = (LocationManager) mContext.getSystemService(mContext.LOCATION_SERVICE);
Criteria criteria = new Criteria();
Location location = locationManager.getLastKnownLocation(locationManager.getBestProvider(criteria, false));
if (location != null)
{
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(
new LatLng(location.getLatitude(), location.getLongitude()), 17));
CameraPosition cameraPosition = new CameraPosition.Builder()
// Sets the center of the map to location user
.target(new LatLng(location.getLatitude(), location.getLongitude()))
.zoom(17) // Sets the zoom
//.bearing(90) // Sets the orientation of the camera to east
//.tilt(40) // Sets the tilt of the camera to 30 degrees
.build(); // Creates a CameraPosition from the builder
mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
}
mMap.setMyLocationEnabled(true);
mMap.getUiSettings().setMyLocationButtonEnabled(false);
}
if (null != mClient)
mClient.close();
}
}
}
Map的布局（fragment_mapa.xml）是：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff"
android:orientation="vertical"
android:id="@+id/container">
<fragment
android:id="@+id/map"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
可能有什么不对？提前谢谢！
答案 0 :(得分：1)
根据帖子How to put Google Maps V2 on a Fragment Using ViewPager（参见Brandon Yang的回答），我使用MapView更改了MapaFragment.java代码，并且它有效。像这样：
public class MapaFragment extends Fragment {
Context mContext;
private GoogleMap mMap;
MapView mMapView;
private Location location;
private final static String URL = "api que retorna JSON";
public static final String TAG = "MapaFragment";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_mapa, container, false);
mMapView = (MapView) rootView.findViewById(R.id.mapView);
mMapView.onCreate(savedInstanceState);
mMapView.onResume();// needed to get the map to display immediately
try {
MapsInitializer.initialize(getActivity().getApplicationContext());
} catch (Exception e) {
e.printStackTrace();
}
mMap = mMapView.getMap();
new HttpGetTask().execute(URL);
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mContext = activity;
}
@Override
public void onResume() {
super.onResume();
mMapView.onResume();
}
@Override
public void onPause() {
super.onPause();
mMapView.onPause();
}
@Override
public void onDestroy() {
super.onDestroy();
mMapView.onDestroy();
}
@Override
public void onLowMemory() {
super.onLowMemory();
mMapView.onLowMemory();
}
private class HttpGetTask extends AsyncTask<String, Void, List<PDVRec>> {
AndroidHttpClient mClient = AndroidHttpClient.newInstance("");
@Override
protected List<PDVRec> doInBackground(String... params) {
HttpGet request = new HttpGet(params[0]);
JSONResponseHandler responseHandler = new JSONResponseHandler();
try {
// Get data in JSON format
// Parse data into a list
return mClient.execute(request, responseHandler);
} catch (ClientProtocolException e) {
Log.i(TAG, "ClientProtocolException");
} catch (IOException e) {
Log.i(TAG, "IOException");
}
return null;
}
@Override
protected void onPostExecute(List<PDVRec> result) {
if (null != mMap) {
for (PDVRec rec : result) {
mMap.addMarker(new MarkerOptions()
// Set the Marker's position
.position(new LatLng(rec.getLat(), rec.getLng()))
// Set the title of the Marker's information window
.title(String.valueOf(rec.getNome_PDV()))
// Set the icon for the Marker
.icon(BitmapDescriptorFactory.fromResource(R.drawable.currentlocation_icon)));
}
LocationManager locationManager = (LocationManager) mContext.getSystemService(mContext.LOCATION_SERVICE);
Criteria criteria = new Criteria();
Location location = locationManager.getLastKnownLocation(locationManager.getBestProvider(criteria, false));
if (location != null)
{
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(
new LatLng(location.getLatitude(), location.getLongitude()), 17));
CameraPosition cameraPosition = new CameraPosition.Builder()
// Sets the center of the map to location user
.target(new LatLng(location.getLatitude(), location.getLongitude()))
.zoom(17) // Sets the zoom
.build(); // Creates a CameraPosition from the builder
mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
}
mMap.setMyLocationEnabled(true);
mMap.getUiSettings().setMyLocationButtonEnabled(false);
}
if (null != mClient)
mClient.close();
}
}
}
还有fragment_mapa.xml：
<com.google.android.gms.maps.MapView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/mapView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
也许需要更好地组织代码，但这样就可以在Fragment中完美地加载地图。