android map初始化時發生錯誤

Question

java.lang.RuntimeException：無法啓動活動ComponentInfo {in.jainrishabh.noteelite/in.jainrishabh.noteelite.MapView}：java.lang.NullPointerException：試圖調用虛擬方法'void com .google.android.gms.maps.GoogleMap.setOnMapClickListener（com.google.android.gms .maps.GoogleMap $ OnMapClickListener）」上一個空對象引用

人知道爲什麼我得到空指針異常

GoogleMap googleMap; 
SharedPreferences sharedPreferences; 
int locationCount = 0; 
private ArrayList<UserDetailsPojo> pojoArrayList; 
private float latia; 
private float longia; 
private Editor editor; 

SharedPreferences prefs; 
float lat; 
float lng; 

String lat_temp; 
String long_temp; 

private ListView userNamesListView; 
private ListAdapter userListAdapter; 

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

    prefs = this.getSharedPreferences("sharedpref", Context.MODE_PRIVATE); 

    latia = prefs.getFloat("latitude", -34); 
    longia = prefs.getFloat("longitude", 151); 

    LatLng myLocation = new LatLng(latia, longia); 

    pojoArrayList = new ArrayList<UserDetailsPojo>(); 

    // For the third argument, we need a List that contains Strings. 
    //We decided to display undergraduates names on the ListView. 
    //Therefore we need to create List that contains undergraduates names 
    userListAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, populateList()); 

    //Toast.makeText(getApplicationContext(), "lati is:"+latia, Toast.LENGTH_LONG).show(); 
    // Getting Google Play availability status 
    int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext()); 

    // Showing status 
    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 of activity_main.xml 
     MapFragment fm = (MapFragment) getFragmentManager().findFragmentById(R.id.map); 

     // Getting GoogleMap object from the fragment 
     googleMap = fm.getMap(); 

     // Enabling MyLocation Layer of Google Map 
     googleMap.setMyLocationEnabled(true); 

     // Opening the sharedPreferences object 
     sharedPreferences = getSharedPreferences("location", -34); 

     // Getting number of locations already stored 
     locationCount = sharedPreferences.getInt("locationCount", 151); 

     // Getting stored zoom level if exists else return 0 
     String zoom = sharedPreferences.getString("zoom", "0"); 

     // If locations are already saved 
     if(locationCount!=0){ 

      String lat = ""; 
      String lng = ""; 

      // Iterating through all the locations stored 
      for(int i=0;i<locationCount;i++){ 

       // Getting the latitude of the i-th location 
       lat = lat_temp; 


       // Getting the longitude of the i-th location 
       lng = long_temp; 

       // Drawing marker on the map 
       drawMarker(new LatLng(Double.parseDouble(lat), Double.parseDouble(lng))); 
      } 

      // Moving CameraPosition to last clicked position 
      googleMap.moveCamera(CameraUpdateFactory.newLatLng(new LatLng(Double.parseDouble(lat), Double.parseDouble(lng)))); 

      //googleMap.moveCamera(CameraUpdateFactory.newLatLngZoom(myLocation, 13)); 
      // Setting the zoom level in the map on last position is clicked 
      googleMap.animateCamera(CameraUpdateFactory.zoomTo(15)); 
     } 
    } 

    googleMap.setOnMapClickListener(new OnMapClickListener() { 

     @Override 
     public void onMapClick(LatLng point) { 
      locationCount++; 

      // Drawing marker on the map 
      drawMarker(point); 

      /** Opening the editor object to write data to sharedPreferences */ 
      SharedPreferences.Editor editor = sharedPreferences.edit(); 

      // Storing the latitude for the i-th location 
      editor.putString("lat"+ Integer.toString((locationCount-1)), Double.toString(point.latitude)); 

      // Storing the longitude for the i-th location 
      editor.putString("lng"+ Integer.toString((locationCount-1)), Double.toString(point.longitude)); 

      // Storing the count of locations or marker count 
      editor.putInt("locationCount", locationCount); 

      /** Storing the zoom level to the shared preferences */ 
      editor.putString("zoom", Float.toString(googleMap.getCameraPosition().zoom)); 

      /** Saving the values stored in the shared preferences */ 
      editor.commit(); 

      Toast.makeText(getBaseContext(), "Marker is added to the Map", Toast.LENGTH_SHORT).show(); 

     } 
    }); 

    googleMap.setOnMapLongClickListener(new OnMapLongClickListener() { 
     @Override 
     public void onMapLongClick(LatLng point) { 

      // Removing the marker and circle from the Google Map 
      googleMap.clear(); 

      // Opening the editor object to delete data from sharedPreferences 
      SharedPreferences.Editor editor = sharedPreferences.edit(); 

      // Clearing the editor 
      editor.clear(); 

      // Committing the changes 
      editor.commit(); 

      // Setting locationCount to zero 
      locationCount=0; 

     } 
    }); 
} 

private void drawMarker(LatLng point){ 
    // Creating an instance of MarkerOptions 
    MarkerOptions markerOptions = new MarkerOptions(); 

    // Setting latitude and longitude for the marker 
    markerOptions.position(point); 

    // Adding marker on the Google Map 
    googleMap.addMarker(markerOptions); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 

public List<String> populateList(){ 

    // We have to return a List which contains only String values. Lets create a List first 
    List<String> userNamesList = new ArrayList<String>(); 

    // First we need to make contact with the database we have created using the DbHelper class 
    AndroidOpenDbHelper openHelperClass = new AndroidOpenDbHelper(this); 

    // Then we need to get a readable database 
    SQLiteDatabase sqliteDatabase = openHelperClass.getReadableDatabase(); 

    // We need a a guy to read the database query. Cursor interface will do it for us 
    //(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy) 
    Cursor cursor = sqliteDatabase.query(AndroidOpenDbHelper.TABLE_USER, null, null, null, null, null, null); 
    // Above given query, read all the columns and fields of the table 

    startManagingCursor(cursor); 

    // Cursor object read all the fields. So we make sure to check it will not miss any by looping through a while loop 
    while (cursor.moveToNext()) { 
     // In one loop, cursor read one undergraduate all details 
     // Assume, we also need to see all the details of each and every undergraduate 
     // What we have to do is in each loop, read all the values, pass them to the POJO class 
     //and create a ArrayList of undergraduates 



     //int Time = cursor.getInt(cursor.getColumnIndex(AndroidOpenDbHelper.COLUMN_TIME)); 
     double latia = cursor.getDouble(cursor.getColumnIndex(AndroidOpenDbHelper.COLUMN_LATI)); 
     double longia = cursor.getDouble(cursor.getColumnIndex(AndroidOpenDbHelper.COLUMN_LONGI)); 

     // Finish reading one raw, now we have to pass them to the POJO 
     UserDetailsPojo ugPojoClass = new UserDetailsPojo(); 
     ugPojoClass.setLati(latia); 
     ugPojoClass.setLongi(longia); 

// Lets pass that POJO to our ArrayList which contains undergraduates as type 
     pojoArrayList.add(ugPojoClass); 

     lat_temp = Double.toString(latia); 
     long_temp = Double.toString(longia); 
     Log.d("latis1",lat_temp); 
     Log.d("longis1",long_temp); 


    } 

    // If you don't close the database, you will get an error 
    // sqliteDatabase.close(); 

    return userNamesList; 
} 

}

Blockquote

<fragment 
    android:id="@+id/map" 
    android:layout_width="wrap_content" 
    android:layout_height="700dp" 
    android:layout_weight="4" 
    android:name="com.google.android.gms.maps.MapFragment" 
    /> 

這是我的MapView XML

Answer 1

你可能會引用GoogleMap的變量它被實例化之前。嘗試更改第一行
GoogleMap googleMap;
來代替。
GoogleMap googleMap = new GoogleMap（）;
此外，請務必在else案例中設置setOnMapClickListener，使其按預期工作。如果地圖對象不存在（也就是說，如果Google Play服務不可用），則不需要設置事件偵聽器。