mMap.setOnMapClickListener中的空对象错误（this）;

package com.example.mukesh.airpollution;




import android.graphics.Color;
import android.os.Bundle;
 import android.support.v4.app.FragmentActivity;

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.MapFragment;
 import com.google.android.gms.maps.OnMapReadyCallback;
 import com.google.android.gms.maps.model.CameraPosition;
 import com.google.android.gms.maps.model.LatLng;
 import com.google.android.gms.maps.model.LatLngBounds;
 import com.google.android.gms.maps.model.Polygon;
 import com.google.android.gms.maps.model.PolygonOptions;
 import com.google.maps.android.PolyUtil;
 import java.util.List;

 import java.util.ArrayList;

 public class MapsActivity extends FragmentActivity
    implements OnMapClickListener, OnMapReadyCallback {

//final int RQS_GooglePlayServices = 1;
private GoogleMap mMap;
//private GoogleMap googleMap;



boolean markerClicked;
PolygonOptions polygonOptions;
Polygon polygon;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    // 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);



    MapFragment mapFragment = (MapFragment)        getFragmentManager().findFragmentById(R.id.map);
    mapFragment.getMapAsync((OnMapReadyCallback) this);

    mMap.setOnMapClickListener(this);
  //  MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
   // mapFragment.getMapAsync(this);
}

@Override
public void onMapReady(GoogleMap googleMap)
{
    mMap = googleMap;
    ArrayList<Polygon> polygonList = new ArrayList<>();
    Polygon polygon = mMap.addPolygon(new PolygonOptions()
                    .add(new LatLng(28.555335, 76.798553), new LatLng(28.830117, 76.935883), new LatLng(28.882919, 77.080078), new LatLng(28.868489, 77.220154), new LatLng(28.714438, 77.328644), new LatLng(28.519141, 77.3698434), (new LatLng(28.399615, 77.196808)), (new LatLng(28.555335, 76.798553)))
                    .strokeColor(Color.RED)

            //    .fillColor(Color.BLUE)
            //
    );



    // ArrayList<Polygon> polygonList = new ArrayList<>();
    Polygon p1 = mMap.addPolygon(new PolygonOptions()
            .add(new LatLng(28.882919, 77.080078), new LatLng(28.752972,  77.078705), new LatLng(28.714438, 77.328644), new LatLng(28.868489, 77.220154),new LatLng(28.882919, 77.080078))

            .strokeColor(Color.RED)

            .fillColor(Color.BLUE));

    // ArrayList<Polygon> polygonList = new ArrayList<>();
    Polygon p2 = mMap.addPolygon(new PolygonOptions()
                    .add(new LatLng(28.882919, 77.080078), new LatLng(28.752972, 77.078705), new LatLng(28.830117, 76.935883), new LatLng(28.882919, 77.080078))

                    .strokeColor(Color.RED)

            //.fillColor(Color.BLUE)
    );
    Polygon p3 = mMap.addPolygon(new PolygonOptions()
                    .add(new LatLng(28.555335, 76.798553), new LatLng(28.752972, 77.078705), new LatLng(28.830117, 76.935883), new LatLng(28.555335, 76.798553))

                    .strokeColor(Color.RED)

            // .fillColor(Color.BLUE)
    );
    final LatLng SYDNEY = new LatLng(28.6139,77.2090);
    final LatLng MOUNTAIN_VIEW = new LatLng(28.6387, 77.0941);

    final LatLngBounds.Builder bounds;
    final LatLng s=new LatLng(28.643353 ,77.446747);
    bounds = new LatLngBounds.Builder();
    bounds.include(new LatLng(28.643353, 77.446747));
    bounds.include(new LatLng(28.509488, 76.823273));




      mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(SYDNEY, 10));


    mMap.animateCamera(CameraUpdateFactory.zoomIn());


     mMap.animateCamera(CameraUpdateFactory.zoomTo(10), 2000, null);


      CameraPosition cameraPosition = new CameraPosition.Builder()
              .target(MOUNTAIN_VIEW)      
            .zoom(10)                  
            .bearing(90)                
            .tilt(30)                  
            .build();                  
                                                                                       mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));











    mMap.setOnCameraChangeListener(new GoogleMap.OnCameraChangeListener() {

                                       @Override
                                       public void onCameraChange(CameraPosition arg0) {
                                           // Move camera.
                                           // googleMap.moveCamera(CameraUpdateFactory.newLatLngBounds(bounds.build(),
                                           if (arg0.zoom >= 10) ;

                                           else if (arg0.zoom < 9) {
                                               CameraPosition cameraPosition1 = new CameraPosition.Builder()
                                                       .target(MOUNTAIN_VIEW)      // Sets the center of the map to Mountain View
                                                       .zoom(12)                   // Sets the zoom
                                                       .bearing(90)                // Sets the orientation of the camera to east
                                                       .tilt(30)                   // Sets the tilt of the camera to 30 degrees
                                                       .build();                   // Creates a CameraPosition from the builder
                                               mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition1));

                                           }
                                           // Remove listener to prevent position reset on camera move.
                                           //  googleMap.setOnCameraChangeListener(googleMap.moveCamera(CameraUpdateFactory.newLatLngBounds(bounds.build(),12)));


                                           //googleMap.(latlngbounds);
                                       }

                                   }

    );

}



@Override
public void onMapClick(LatLng point) {
    Polygon polygon = mMap.addPolygon(new PolygonOptions()
            .add(new LatLng(0, 0), new LatLng(0, 5), new LatLng(3, 5), new LatLng(0, 0)));

    Polygon p1 = mMap.addPolygon(new PolygonOptions()
            .add(new LatLng(0, 0), new LatLng(0, 5), new LatLng(3, 5), new LatLng(0, 0)));

    Polygon p2 = mMap.addPolygon(new PolygonOptions()
            .add(new LatLng(0, 0), new LatLng(0, 5), new LatLng(3, 5), new LatLng(0, 0)));

    Polygon p3 = mMap.addPolygon(new PolygonOptions()
            .add(new LatLng(0, 0), new LatLng(0, 5), new LatLng(3, 5), new LatLng(0, 0)));


    //CHANGE POLYGON SPECIFICATIONS
    //ADD ALL POLYGONS


    List<LatLng> points = polygon.getPoints();
    List<LatLng> points1 = p1.getPoints();
    List<LatLng> points2 = p2.getPoints();
    List<LatLng> points3 = p3.getPoints();


    if (PolyUtil.containsLocation(point, points, false)) {
        //Do SOMETHING...
    } else if (PolyUtil.containsLocation(point, points1, false)) {
        //Do SOMETHING...
    }
    if (PolyUtil.containsLocation(point, points2, false)) {
        //Do SOMETHING...
    }
    if (PolyUtil.containsLocation(point, points3, false)) {
        //Do SOMETHING...
    }


}

}

在这一行中获得错误
mMap.setOnMapClickListener(this);

java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.mukesh.airpollution / com.example.mukesh.airpollution.MapsActivity}：java.lang.NullPointerException：尝试调用虚方法'void com.google.android android.app.ActivityThread上android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2325）上的空对象引用上的.gms.maps.GoogleMap.setOnMapClickListener（com.google.android.gms.maps.GoogleMap $ OnMapClickListener）' .handleLaunchActivity（ActivityThread.java:2387）在Android.app.Handler.dispatchMessage的android.app.ActivityThread.access $ 800（ActivityThread.java:151）android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1303） （Handler.java:102）在android.app.Looper.loop（Looper.java:135）的android.app.ActivityThread.main（ActivityThread.java:5254）java.lang.reflect.Method.invoke（Native Method） ）在java.lang.reflect.Method.invoke（Method.java:372）的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:90） 3）at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:698）引起：java.lang.NullPointerException：尝试调用虚方法'void com.google.android.gms.maps.GoogleMap.setOnMapClickListener （com.google.android.gms.maps.GoogleMap $ OnMapClickListener）'在android.app.Activity.performCreate上的com.example.mukesh.airpollution.MapsActivity.onCreate（MapsActivity.java:58）上的空对象引用上.java：5990）在Android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2387）的android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1106）android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2278）在android.app.ActivityThread.access $ 800（ActivityThread.java:151）android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1303）在android.os.Handler.dispatchMessage（Handler.java:102）在android .os.Looper.loop（Looper.java:135）位于android.app.ActivityThread.main（ActivityThread.java:5254）的java.lang.reflect.Method.invoke（N （a）方法）在com.android.internal.os的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:903）的java.lang.reflect.Method.invoke（Method.java:372）中 . ZygoteInit.main（ZygoteInit.java:698）