我正在制作一个 map 应用程序，其中显示两点之间的路线(动态)。在这里，我从数据库中检索纬度和经度(可以随时间变化)。这是一个大学项目，所以没有在安全部分工作。这是用于导航的 java 文件:

public class NavigationActivity extends AppCompatActivity implements OnMapReadyCallback,
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener,
        GoogleMap.OnMarkerDragListener,
        GoogleMap.OnMapLongClickListener,
        LocationListener {

    private GoogleMap mMap;
    GoogleApiClient mGoogleApiClient;
    Location mLastLocation;
    Marker mCurrLocationMarker;
    LocationRequest mLocationRequest;
    private double longitude;
    private double latitude;
    private double fromLongitude;
    private double fromLatitude;
    private double toLongitude;
    private double toLatitude;
    private static final String LOGIN_URL = "http://192.168.211.1/xyz/lat.php";
    private static final String LOGIN_URLS = "http://192.168.211.1/xyz/lng.php";
    public static final String KEY_MYNAME = "User";
    public static final String LAT = "lat";
    public static final String LANG = "lang";
    public LocationManager locationManager;
    public Criteria criteria;
    public String bestProvider;
    private static final String TAG = NavigationActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_navigation);
        getLocation();
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            checkLocationPermission();
        }
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
    }
    public static boolean isLocationEnabled(Context context)
    {
        return true;
    }
    protected void getLocation() {
        if (isLocationEnabled(NavigationActivity.this)) {
            locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
            criteria = new Criteria();
            bestProvider = String.valueOf(locationManager.getBestProvider(criteria, true)).toString();
            //You can still do this if you like, you might get lucky:
            Location location = locationManager.getLastKnownLocation(bestProvider);
            if (location != null) {
                Log.e("TAG", "GPS is on");
                latitude = location.getLatitude();
                longitude = location.getLongitude();
//                Toast.makeText(NavigationActivity.this, "latitude:" + latitude + " longitude:" + longitude, Toast.LENGTH_SHORT).show();
                //Trying to send the data to the database
                final StringRequest stringrequest=new StringRequest(Request.Method.POST,LOGIN_URL,new Response.Listener<String>(){
                    @Override
                    public void onResponse(String s) {
                        if (!s.equalsIgnoreCase("updated")) {
                            Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();
                            getPoints();
                        }
                    }
                },
                        new Response.ErrorListener() {
                            @Override
                            public void onErrorResponse(VolleyError volleyError) {
                                Toast.makeText(getApplicationContext(), volleyError.toString(), Toast.LENGTH_LONG).show();
                            }
                        }){
                    protected Map<String,String> getParams(){
                        Map<String,String>params=new HashMap<String, String>();
                        SharedPreferences sharedPreferences = NavigationActivity.this.getSharedPreferences(Config.SHARED_PREF_NAME, Context.MODE_PRIVATE);
                        String KEY_MYUSERNAME = sharedPreferences.getString(Config.EMAIL_SHARED_PREF, "Not Found");
                        params.put(LAT, String.valueOf(latitude));
                        params.put(LANG, String.valueOf(longitude));
                        params.put(KEY_MYNAME, KEY_MYUSERNAME);
                        return params;
                    }
                };
                RequestQueue requestQueue= Volley.newRequestQueue(this);
                requestQueue.add(stringrequest);
            } else {
                //This is what you need:
                if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                    // TODO: Consider calling
                    //    ActivityCompat#requestPermissions
                    // here to request the missing permissions, and then overriding
                    //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
                    //                                          int[] grantResults)
                    // to handle the case where the user grants the permission. See the documentation
                    // for ActivityCompat#requestPermissions for more details.
                    return;
                }
                locationManager.requestLocationUpdates(bestProvider, 1000, 0, this);
            }
        }
        else
        {
            //prompt user to enable location....
            //.................
        }
    }
    @Override
    protected void onStart() {
        mGoogleApiClient.connect();
        super.onStart();
    }
    @Override
    protected void onStop() {
        mGoogleApiClient.disconnect();
        super.onStop();
    }
    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);

        //Initialize Google Play Services
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (ContextCompat.checkSelfPermission(this,
                    Manifest.permission.ACCESS_FINE_LOCATION)
                    == PackageManager.PERMISSION_GRANTED) {
                buildGoogleApiClient();
                mMap.setMyLocationEnabled(true);
            }
        } else {
            buildGoogleApiClient();
            mMap.setMyLocationEnabled(true);
        }
    }
    protected synchronized void buildGoogleApiClient() {
        mGoogleApiClient = new GoogleApiClient.Builder(this)
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
        mGoogleApiClient.connect();
    }
    @Override
    public void onConnected(Bundle bundle) {
        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(1000);
        mLocationRequest.setFastestInterval(1000);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
//        if (ContextCompat.checkSelfPermission(this,
//                Manifest.permission.ACCESS_FINE_LOCATION)
//                == PackageManager.PERMISSION_GRANTED) {
//            LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
//        }
    }
    private void getPoints() {
        //Getting the URL
        fromLatitude = latitude;
        fromLongitude = longitude;
        //To get to latitude
        StringRequest stringRequests = new StringRequest(Request.Method.POST, LOGIN_URL,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        if (response.equalsIgnoreCase("Connection Error")) {
                            Toast.makeText(NavigationActivity.this, response, Toast.LENGTH_SHORT).show();
                        }
                        else {
                            toLatitude = Double.parseDouble(response);
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(NavigationActivity.this, error.toString(), Toast.LENGTH_LONG).show();
                    }
                }) {
            @Override
            protected Map<String, String> getParams() {
                SharedPreferences sharedPreferences = NavigationActivity.this.getSharedPreferences(Config.SHARED_PREF_NAME, Context.MODE_PRIVATE);
                String KEY_MYUSERNAME = sharedPreferences.getString(Config.EMAIL_SHARED_PREF,"Not Found");
                Map<String,String> params = new HashMap<String, String>();
                params.put(KEY_MYNAME,KEY_MYUSERNAME);
                return params;
            }
        };
        RequestQueue requestQueues = Volley.newRequestQueue(this);
        requestQueues.add(stringRequests);
        StringRequest stringRequestss = new StringRequest(Request.Method.POST, LOGIN_URLS,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        if (response.equalsIgnoreCase("Connection Error")) {
                            Toast.makeText(NavigationActivity.this, response, Toast.LENGTH_SHORT).show();
                        }
                        else {
                            toLongitude = Double.parseDouble(response);
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(NavigationActivity.this, error.toString(), Toast.LENGTH_LONG).show();
                    }
                }) {
            @Override
            protected Map<String, String> getParams() {
                SharedPreferences sharedPreferences = NavigationActivity.this.getSharedPreferences(Config.SHARED_PREF_NAME, Context.MODE_PRIVATE);
                String KEY_MYUSERNAME = sharedPreferences.getString(Config.EMAIL_SHARED_PREF,"Not Found");
                Map<String,String> params = new HashMap<String, String>();
                params.put(KEY_MYNAME,KEY_MYUSERNAME);
                return params;
            }
        };
        RequestQueue requestQueuess = Volley.newRequestQueue(this);
        requestQueuess.add(stringRequestss);
        getDirections();
    }
    private void getDirections() {
        double flat = fromLatitude;
        double flong = fromLongitude;
        double tlat = toLatitude;
        double tlong = toLongitude;
        LatLng origin = new LatLng(flat, flong);
        LatLng dest = new LatLng(tlat, tlong);
        String url = getDirectionsUrl(origin, dest);
        DownloadTask downloadTask = new DownloadTask();
        // Start downloading json data from Google Directions API
        downloadTask.execute(url);
    }
    private String getDirectionsUrl(LatLng origin,LatLng dest){
        // Origin of route
        String str_origin = "origin="+origin.latitude+","+origin.longitude;
        // Destination of route
        String str_dest = "destination="+dest.latitude+","+dest.longitude;
        // Sensor enabled
        String sensor = "sensor=false";
        // Building the parameters to the web service
        String parameters = str_origin+"&"+str_dest+"&"+sensor;
        // Output format
        String output = "json";
        // Building the url to the web service
        String url = "https://maps.googleapis.com/maps/api/directions/"+output+"?"+parameters;
        return 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){
        }finally{
            iStream.close();
            urlConnection.disconnect();
        }
        return data;
    }
    // Fetches data from url passed
    private class DownloadTask extends AsyncTask<String, Void, String> {
        // Downloading data in non-ui thread
        @Override
        protected String doInBackground(String... url) {
            // For storing data from web service
            String data = "";
            try{
                // Fetching the data from web service
                data = downloadUrl(url[0]);
            }catch(Exception e){
                Log.d("Background Task",e.toString());
            }
            return data;
        }
        // Executes in UI thread, after the execution of
        // doInBackground()
        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            ParserTask parserTask = new ParserTask();
            // Invokes the thread for parsing the JSON data
            parserTask.execute(result);
        }
    }
    /** A class to parse the Google Places in JSON format */
    private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String,String>>> >{
        // Parsing the data in non-ui thread
        @Override
        protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) {
            JSONObject jObject;
            List<List<HashMap<String, String>>> routes = null;
            try{
                jObject = new JSONObject(jsonData[0]);
                DirectionsJSONParser parser = new DirectionsJSONParser();
                // Starts parsing data
                routes = parser.parse(jObject);
            }catch(Exception e){
                e.printStackTrace();
            }
            return routes;
        }
        // Executes in UI thread, after the parsing process
        @Override
        protected void onPostExecute(List<List<HashMap<String, String>>> result) {
            ArrayList<LatLng> points = null;
            PolylineOptions lineOptions = null;
            MarkerOptions markerOptions = new MarkerOptions();
            // Traversing through all the routes
            for(int i=0;i<result.size();i++){
                points = new ArrayList<LatLng>();
                lineOptions = new PolylineOptions();
                // Fetching i-th route
                List<HashMap<String, String>> path = result.get(i);
                // Fetching all the points in i-th route
                for(int j=0;j<path.size();j++){
                    HashMap<String,String> point = path.get(j);
                    double lat = Double.parseDouble(point.get("lat"));
                    double lng = Double.parseDouble(point.get("lng"));
                    LatLng position = new LatLng(lat, lng);
                    points.add(position);
                }
                // Adding all the points in the route to LineOptions
                lineOptions.addAll(points);
                lineOptions.width(2);
                lineOptions.color(Color.RED);
            }
            // Drawing polyline in the Google Map for the i-th route
                mMap.addPolyline(lineOptions);
        }
    }
        @Override
    public void onConnectionSuspended(int i) {
    }
    @Override
    public void onLocationChanged(final Location location) {
        getLocation();
        mLastLocation = location;
        if (mCurrLocationMarker != null) {
            mCurrLocationMarker.remove();
        }
        //Place current location marker
        LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
        MarkerOptions markerOptions = new MarkerOptions();
        markerOptions.position(latLng);
        markerOptions.title("Current Position");
        markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
        mCurrLocationMarker = mMap.addMarker(markerOptions);
        Toast.makeText(NavigationActivity.this, String.valueOf(location.getLatitude()), Toast.LENGTH_LONG).show();
        //move map camera
        mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
        mMap.animateCamera(CameraUpdateFactory.zoomTo(11));
        //stop location updates
        if (mGoogleApiClient != null) {                LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, (com.google.android.gms.location.LocationListener) this);
        }
    }
    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {
        Toast.makeText(NavigationActivity.this, "Connection Lost", Toast.LENGTH_LONG).show();
    }
    public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;
    public boolean checkLocationPermission() {
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION)
                != PackageManager.PERMISSION_GRANTED) {
            // Asking user if explanation is needed
            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                    Manifest.permission.ACCESS_FINE_LOCATION)) {
                // Show an explanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission
                //Prompt the user once explanation has been shown
                ActivityCompat.requestPermissions(this,
                        new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                        MY_PERMISSIONS_REQUEST_LOCATION);
            } else {
                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(this,
                        new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                        MY_PERMISSIONS_REQUEST_LOCATION);
            }
            return false;
        } else {
            return true;
        }
    }
    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST_LOCATION: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    // permission was granted. Do the
                    // contacts-related task you need to do.
                    if (ContextCompat.checkSelfPermission(this,
                            Manifest.permission.ACCESS_FINE_LOCATION)
                            == PackageManager.PERMISSION_GRANTED) {
                        if (mGoogleApiClient == null) {
                            buildGoogleApiClient();
                        }
                        mMap.setMyLocationEnabled(true);
                    }
                } else {
                    // Permission denied, Disable the functionality that depends on this permission.
                    Toast.makeText(this, "permission denied", Toast.LENGTH_LONG).show();
                }
                return;
            }
        }
    }
}

这是我的日志:

03-24 15:00:51.174 9970-9970/com.xyz.user.xyz E/AndroidRuntime: FATAL EXCEPTION: main
                                                                    Process: com.xyz.user.xyz, PID: 9970
                                                                    java.lang.NullPointerException: PolylineOptions cannot be null.
                                                                        at com.google.maps.api.android.lib6.common.k.a(:com.google.android.gms.DynamiteModulesB:42)
                                                                        at com.google.maps.api.android.lib6.impl.dp.<init>(:com.google.android.gms.DynamiteModulesB:146)
                                                                        at com.google.maps.api.android.lib6.impl.az.a(:com.google.android.gms.DynamiteModulesB:931)
                                                                        at com.google.android.gms.maps.internal.l.onTransact(:com.google.android.gms.DynamiteModulesB:137)
                                                                        at android.os.Binder.transact(Binder.java:380)
                                                                        at com.google.android.gms.maps.internal.IGoogleMapDelegate$zza$zza.addPolyline(Unknown Source)
                                                                        at com.google.android.gms.maps.GoogleMap.addPolyline(Unknown Source)
                                                                        at com.xyz.user.xyz.NavigationActivity$ParserTask.onPostExecute(NavigationActivity.java:474)
                                                                        at com.xyz.user.xyz.NavigationActivity$ParserTask.onPostExecute(NavigationActivity.java:420)
                                                                        at android.os.AsyncTask.finish(AsyncTask.java:636)
                                                                        at android.os.AsyncTask.access$500(AsyncTask.java:177)
                                                                        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:653)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                        at android.os.Looper.loop(Looper.java:135)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:5343)
                                                                        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:905)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)

谁能给我一些解决方案？

我尝试使用下面的代码:

if(lineOptions!=null)
{
mMap.addPolyline(lineOptions);
}

上面的代码有助于避免应用程序崩溃，但它仍然无法帮助我绘制这些点之间的路线。

检索到的数据是正确的，我用toast检查过。

最佳答案

我检查了你的代码，发现了一些导致崩溃的问题，首先你初始化了 null ArrayList<LatLng>points=null和 PolylineOptions lineOptions=null那么如果路径为 null 那么 lineOptions 怎么办？太空了，因此我修复了代码下面的行审查应用它运行它，如果成功享受!

@Override
        protected void onPostExecute(List<List<HashMap<String, String>>> result) {
            ArrayList<LatLng> points = new ArrayList<LatLng>();;
            PolylineOptions lineOptions = new PolylineOptions();;
                lineOptions.width(2);
                lineOptions.color(Color.RED);
            MarkerOptions markerOptions = new MarkerOptions();
            // Traversing through all the routes
            for(int i=0;i<result.size();i++){
                // Fetching i-th route
                List<HashMap<String, String>> path = result.get(i);
                // Fetching all the points in i-th route
                for(int j=0;j<path.size();j++){
                    HashMap<String,String> point = path.get(j);
                    double lat = Double.parseDouble(point.get("lat"));
                    double lng = Double.parseDouble(point.get("lng"));
                    LatLng position = new LatLng(lat, lng);
                    points.add(position);
                }
                // Adding all the points in the route to LineOptions
                lineOptions.addAll(points);

            }
            // Drawing polyline in the Google Map for the i-th route
                if(points.size()!=0)mMap.addPolyline(lineOptions);//to avoid crash
        }

关于android - 折线选项不能为空，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42996662/