主要的Activity类 活动类：
public class MapsActivity extends FragmentActivity implements LocationListener {
GoogleMap mGoogleMap;
Spinner mSprPlaceType;
String[] mPlaceType=null;
String[] mPlaceTypeName=null;
double mLatitude=0;
double mLongitude=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
// Array of place types
mPlaceType = getResources().getStringArray(R.array.place_type);
// Array of place type names
mPlaceTypeName = getResources().getStringArray(R.array.place_type_name);
// Creating an array adapter with an array of Place types
// to populate the spinner
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, mPlaceTypeName);
// Getting reference to the Spinner
mSprPlaceType = (Spinner) findViewById(R.id.spr_place_type);
// Setting adapter on Spinner to set place types
mSprPlaceType.setAdapter(adapter);
Button btnFind;
// Getting reference to Find Button
btnFind = ( Button ) findViewById(R.id.btn_find);
// Getting Google Play availability status
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());
if(status!=ConnectionResult.SUCCESS){ // Google Play Services are not available
int requestCode = 10;
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
dialog.show();
}else { // Google Play Services are available
// Getting reference to the SupportMapFragment
SupportMapFragment fragment = ( SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
// Getting Google Map
mGoogleMap = fragment.getMap();
// Enabling MyLocation in Google Map
mGoogleMap.setMyLocationEnabled(true);
尝试将活动类转换为片段类。 片段类：
public class MapsActivity extends Fragment implements LocationListener{
GoogleMap mGoogleMap;
Spinner mSprPlaceType;
String[] mPlaceType=null;
String[] mPlaceTypeName=null;
double mLatitude=0;
double mLongitude=0;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_main, container, false);
// Array of place types
mPlaceType = getResources().getStringArray(R.array.place_type);
// Array of place type names
mPlaceTypeName = getResources().getStringArray(R.array.place_type_name);
// Creating an array adapter with an array of Place types
// to populate the spinner
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_spinner_dropdown_item, mPlaceTypeName);
// Getting reference to the Spinner
mSprPlaceType = (Spinner) getView().findViewById(R.id.spr_place_type);
// Setting adapter on Spinner to set place types
mSprPlaceType.setAdapter(adapter);
Button btnFind;
// Getting reference to Find Button
btnFind = ( Button ) getView().findViewById(R.id.btn_find);
return rootView;
// Getting Google Play availability status
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity().getBaseContext());
if(status!=ConnectionResult.SUCCESS){ // Google Play Services are not available
int requestCode = 10;
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, getActivity(), requestCode);
dialog.show();
}else { // Google Play Services are available
// Getting reference to the SupportMapFragment
SupportMapFragment fragment = ( SupportMapFragment) getFragmentManager().findFragmentById(R.id.map);
// Getting Google Map
mGoogleMap = fragment.getMap();
// Enabling MyLocation in Google Map
mGoogleMap.setMyLocationEnabled(true);
// Getting LocationManager object from System Service LOCATION_SERVICE
LocationManager locationManager = (LocationManager) getActivity().getSystemService(Context.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 From GPS
Location location = locationManager.getLastKnownLocation(provider);
if(location!=null){
onLocationChanged(location);
}
locationManager.requestLocationUpdates(provider, 20000, 0, this);
// Setting click event lister for the find button
btnFind.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
int selectedPosition = mSprPlaceType.getSelectedItemPosition();
String type = mPlaceType[selectedPosition];
StringBuilder sb = new StringBuilder("https://maps.googleapis.com/maps/api/place/nearbysearch/json?");
sb.append("location="+mLatitude+","+mLongitude);
sb.append("&radius=5000");
sb.append("&types="+type);
sb.append("&sensor=true");
sb.append("&key=AIzaSyBArXqaJg8mngPxdCjt_sckPkKd2GJohmA");
// Creating a new non-ui thread task to download Google place json data
PlacesTask placesTask = new PlacesTask();
// Invokes the "doInBackground()" method of the class PlaceTask
placesTask.execute(sb.toString());
}
});
}
}
/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
HttpURLConnection urlConnection = null;
try{
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while( ( line = br.readLine()) != null){
sb.append(line);
}
data = sb.toString();
br.close();
}catch(Exception e){
Log.d("Exception while downloading url", e.toString());
}finally{
iStream.close();
urlConnection.disconnect();
}
return data;
}
/** A class, to download Google Places */
private class PlacesTask extends AsyncTask<String, Integer, String>{
String data = null;
// Invoked by execute() method of this object
@Override
protected String doInBackground(String... url) {
try{
data = downloadUrl(url[0]);
}catch(Exception e){
Log.d("Background Task",e.toString());
}
return data;
}
// Executed after the complete execution of doInBackground() method
@Override
protected void onPostExecute(String result){
ParserTask parserTask = new ParserTask();
// Start parsing the Google places in JSON format
// Invokes the "doInBackground()" method of the class ParseTask
parserTask.execute(result);
}
}
/** A class to parse the Google Places in JSON format */
private class ParserTask extends AsyncTask<String, Integer, List<HashMap<String,String>>>{
JSONObject jObject;
// Invoked by execute() method of this object
@Override
protected List<HashMap<String,String>> doInBackground(String... jsonData) {
List<HashMap<String, String>> places = null;
PlaceJSONParser placeJsonParser = new PlaceJSONParser();
try{
jObject = new JSONObject(jsonData[0]);
/** Getting the parsed data as a List construct */
places = placeJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
return places;
}
// Executed after the complete execution of doInBackground() method
@Override
protected void onPostExecute(List<HashMap<String,String>> list){
// Clears all the existing markers
mGoogleMap.clear();
for(int i=0;i<list.size();i++){
// Creating a marker
MarkerOptions markerOptions = new MarkerOptions();
// Getting a place from the places list
HashMap<String, String> hmPlace = list.get(i);
// Getting latitude of the place
double lat = Double.parseDouble(hmPlace.get("lat"));
// Getting longitude of the place
double lng = Double.parseDouble(hmPlace.get("lng"));
// Getting name
String name = hmPlace.get("place_name");
// Getting vicinity
String vicinity = hmPlace.get("vicinity");
LatLng latLng = new LatLng(lat, lng);
// Setting the position for the marker
markerOptions.position(latLng);
// Setting the title for the marker.
//This will be displayed on taping the marker
markerOptions.title(name + " : " + vicinity);
// Placing a marker on the touched position
mGoogleMap.addMarker(markerOptions);
}
}
}
public boolean OnCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.activity_main, menu);
return true;
}
@Override
public void onLocationChanged(Location location) {
mLatitude = location.getLatitude();
mLongitude = location.getLongitude();
LatLng latLng = new LatLng(mLatitude, mLongitude);
mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(12));
}
@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
}
} 得到的错误 错误：（82,7）错误：无法访问的语句 错误：（154,2）错误：缺少返回语句
代码：
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity().getBaseContext());
我从活动更改为片段类的内容，为什么应用程序崩溃？
活动类：
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, mPlaceTypeName);
mSprPlaceType = (Spinner) findViewById(R.id.spr_place_type);
btnFind = ( Button ) findViewById(R.id.btn_find);
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
SupportMapFragment fragment = ( SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
片段类：
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.activity_main, container, false);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_spinner_dropdown_item, mPlaceTypeName);
mSprPlaceType = (Spinner) getView().findViewById(R.id.spr_place_type);
btnFind = ( Button ) getView().findViewById(R.id.btn_find);
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getActivity().getBaseContext());
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, getActivity(), requestCode);
SupportMapFragment fragment = ( SupportMapFragment) getFragmentManager().findFragmentById(R.id.map);
LocationManager locationManager = (LocationManager) getActivity().getSystemService(Context.LOCATION_SERVICE);
logcat的：
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{in.wptrafficanalyzer.locationnearby/in.wptrafficanalyzer.locationnearby.MainActivity}: java.lang.ClassCastException: in.wptrafficanalyzer.locationnearby.MainActivity cannot be cast to android.app.Activity
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2515)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5832)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.ClassCastException: in.wptrafficanalyzer.locationnearby.MainActivity cannot be cast to android.app.Activity
at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2505)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
at android.app.ActivityThread.access$900(ActivityThread.java:172)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5832)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
答案 0 :(得分：0)
您需要将return rootView移到onCreateView()的最后一行，因为return语句之后的任何内容都无法访问，因此错误。
您还需要使用rootView.findViewById()代替getView().findViewById()，因为当您使用该方法时尚未创建视图，因此getView()会返回null，并且您的应用程序可能会崩溃。
代码
mSprPlaceType = (Spinner) rootView.findViewById(R.id.spr_place_type);
btnFind = ( Button ) rootView.findViewById(R.id.btn_find);
注意：这不会解决以后可能出现的任何其他问题并导致您的应用崩溃。