Android 谷歌地图 : Unable to start activity ComponentInfo MainActivity}: java. lang.NullPointerException

Question

我在 android 中做应用程序以获取我附近的地方，当我尝试运行时我做了一切但得到了这个异常，我不知道是什么原因导致这个异常

主要 Activity

package com.gas;

public class MainActivity extends Activity implements LocationListener{

    GoogleMap mGoogleMap;
    GoogleMap map;
    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_main);

        mPlaceType = getResources().getStringArray(R.array.place_type);
        mPlaceTypeName = getResources().getStringArray(R.array.place_type_name);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, mPlaceTypeName);
        mSprPlaceType = (Spinner) findViewById(R.id.spr_place_type);
        mSprPlaceType.setAdapter(adapter);

        Button btnFind;
        btnFind = ( Button ) findViewById(R.id.btn_find);
        MapFragment fm=(MapFragment) getFragmentManager().findFragmentById(R.id.map);
        map=fm.getMap();
        map.setMyLocationEnabled(true);
            LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
            Criteria criteria = new Criteria();
            String provider = locationManager.getBestProvider(criteria, true);
            Location location = locationManager.getLastKnownLocation(provider);
            if(location!=null)
                onLocationChanged(location);
            locationManager.requestLocationUpdates(provider, 20000, 0, this);
            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=YOUR_API_KEY");
                    PlacesTask placesTask = new PlacesTask();
                    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);
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.connect();
            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;
    }
    private class PlacesTask extends AsyncTask<String, Integer, String>{
        String data = null;
        @Override
        protected String doInBackground(String... url) {
            try{
                data = downloadUrl(url[0]);
            }catch(Exception e){
                Log.d("Background Task",e.toString());
            }
            return data;
        }
        @Override
        protected void onPostExecute(String result){
            ParserTask parserTask = new ParserTask();
            parserTask.execute(result);
        }
    }

    private class ParserTask extends AsyncTask<String, Integer, List<HashMap<String,String>>>{
        JSONObject jObject;
        @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]);
                places = placeJsonParser.parse(jObject);
            }catch(Exception e){
                Log.d("Exception",e.toString());
            }
            return places;
        }
        @Override
        protected void onPostExecute(List<HashMap<String,String>> list){
            mGoogleMap.clear();

            for(int i=0;i<list.size();i++){
                MarkerOptions markerOptions = new MarkerOptions();
                HashMap<String, String> hmPlace = list.get(i);
                double lat = Double.parseDouble(hmPlace.get("lat"));
                double lng = Double.parseDouble(hmPlace.get("lng"));
                String name = hmPlace.get("place_name");
                String vicinity = hmPlace.get("vicinity");
                LatLng latLng = new LatLng(lat, lng);
                markerOptions.position(latLng);
                markerOptions.title(name + " : " + vicinity);
                mGoogleMap.addMarker(markerOptions);
            }
        }
    }

    @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));
    }
}

list

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.gas"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="15"
        android:targetSdkVersion="15" />

    <permission
        android:name="com.gas.permission.MAPS_RECEIVE"
        android:protectionLevel="signature" />

    <uses-feature
        android:glEsVersion="0x00020000"
        android:required="true" />
    <uses-permission android:name="com.gas.permission.MAPS_RECEIVE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" />
    <uses-permission android:name="android.permission.com.google.android.providers.gsf.permission.READ_GSERVICES" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <uses-feature
        android:name="android.hardware.location"
        android:required="false" />
    <uses-feature
        android:name="android.hardware.location.network"
        android:required="false" />
    <uses-feature android:name="android.hardware.location.gps" />
    <uses-feature
        android:name="android.hardware.wifi"
        android:required="false" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.gas.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="AIzaSyAtg_enu6Ox2l-WMyT-rpk_dUytQvSZaEw" />


    </application>
</manifest> 

放置JasonParser

package com.gas;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

public class PlaceJSONParser {

    /** Receives a JSONObject and returns a list */
    public List<HashMap<String,String>> parse(JSONObject jObject){

        JSONArray jPlaces = null;
        try {
            /** Retrieves all the elements in the 'places' array */
            jPlaces = jObject.getJSONArray("results");
        } catch (JSONException e) {
            e.printStackTrace();
        }
        /** Invoking getPlaces with the array of json object
        * where each json object represent a place
        */
        return getPlaces(jPlaces);
    }

    private List<HashMap<String, String>> getPlaces(JSONArray jPlaces){
        int placesCount = jPlaces.length();
        List<HashMap<String, String>> placesList = new ArrayList<HashMap<String,String>>();
        HashMap<String, String> place = null;

        /** Taking each place, parses and adds to list object */
        for(int i=0; i<placesCount;i++){
            try {
                /** Call getPlace with place JSON object to parse the place */
                place = getPlace((JSONObject)jPlaces.get(i));
                placesList.add(place);

            } catch (JSONException e) {
                e.printStackTrace();
            }
        }

        return placesList;
    }

    /** Parsing the Place JSON object */
    private HashMap<String, String> getPlace(JSONObject jPlace){

        HashMap<String, String> place = new HashMap<String, String>();
        String placeName = "-NA-";
        String vicinity="-NA-";
        String latitude="";
        String longitude="";

        try {
            // Extracting Place name, if available
            if(!jPlace.isNull("name")){
                placeName = jPlace.getString("name");
            }

            // Extracting Place Vicinity, if available
            if(!jPlace.isNull("vicinity")){
                vicinity = jPlace.getString("vicinity");
            }

            latitude = jPlace.getJSONObject("geometry").getJSONObject("location").getString("lat");
            longitude = jPlace.getJSONObject("geometry").getJSONObject("location").getString("lng");

            place.put("place_name", placeName);
            place.put("vicinity", vicinity);
            place.put("lat", latitude);
            place.put("lng", longitude);

        } catch (JSONException e) {
            e.printStackTrace();
        }
        return place;
    }
}

布局

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <Spinner
        android:id="@+id/spr_place_type"
        android:layout_width="wrap_content"
        android:layout_height="60dp"
        android:layout_alignParentTop="true" />

    <Button
        android:id="@+id/btn_find"
        android:layout_width="wrap_content"
        android:layout_height="60dp"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@id/spr_place_type"
        android:text="@string/str_btn_find" />

    <fragment
        android:id="@+id/map"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/spr_place_type"
        class="com.google.android.gms.maps.MapFragment" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

日志猫

05-23 04:19:27.233: D/AbsListView(4213): Get MotionRecognitionManager
05-23 04:19:27.573: D/AndroidRuntime(4213): Shutting down VM
05-23 04:19:27.573: W/dalvikvm(4213): threadid=1: thread exiting with uncaught             exception (group=0x40c18a68)
05-23 04:19:27.573: E/AndroidRuntime(4213): FATAL EXCEPTION: main
05-23 04:19:27.573: E/AndroidRuntime(4213): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gas/com.gas.MainActivity}: java.lang.NullPointerException
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.ActivityThread.access$600(ActivityThread.java:128)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.os.Looper.loop(Looper.java:137)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.ActivityThread.main(ActivityThread.java:4517)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at java.lang.reflect.Method.invokeNative(Native Method)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at java.lang.reflect.Method.invoke(Method.java:511)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at dalvik.system.NativeStart.main(Native Method)
05-23 04:19:27.573: E/AndroidRuntime(4213): Caused by: java.lang.NullPointerException
05-23 04:19:27.573: E/AndroidRuntime(4213):     at com.gas.MainActivity.onLocationChanged(MainActivity.java:375)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at com.gas.MainActivity.onCreate(MainActivity.java:194)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.Activity.performCreate(Activity.java:4470)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
05-23 04:19:27.573: E/AndroidRuntime(4213):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
05-23 04:19:27.573: E/AndroidRuntime(4213):     ... 11 more
05-23 04:21:46.973: D/AbsListView(4760): Get MotionRecognitionManager
05-23 04:21:47.253: D/AndroidRuntime(4760): Shutting down VM
05-23 04:21:47.253: W/dalvikvm(4760): threadid=1: thread exiting with uncaught exception (group=0x40c18a68)
05-23 04:21:47.253: E/AndroidRuntime(4760): FATAL EXCEPTION: main
05-23 04:21:47.253: E/AndroidRuntime(4760): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gas/com.gas.MainActivity}: java.lang.NullPointerException
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.ActivityThread.access$600(ActivityThread.java:128)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.os.Looper.loop(Looper.java:137)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.ActivityThread.main(ActivityThread.java:4517)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at java.lang.reflect.Method.invokeNative(Native Method)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at java.lang.reflect.Method.invoke(Method.java:511)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at dalvik.system.NativeStart.main(Native Method)
05-23 04:21:47.253: E/AndroidRuntime(4760): Caused by: java.lang.NullPointerException
05-23 04:21:47.253: E/AndroidRuntime(4760):     at com.gas.MainActivity.onLocationChanged(MainActivity.java:375)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at com.gas.MainActivity.onCreate(MainActivity.java:194)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.Activity.performCreate(Activity.java:4470)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
05-23 04:21:47.253: E/AndroidRuntime(4760):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
05-23 04:21:47.253: E/AndroidRuntime(4760):     ... 11 more

Answer 1

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mGoogleMap = fragment.getMap();

当您尝试移动相机时，您的 mGoogleMap 在方法 onLocationChanged 中为 null -> MainActivity 中的第 375 行:

mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));