轉換setOnCameraChangeListener至3個新的相機聽衆

Question

在播放服務，地圖9.4.0版本的API，他們更換GoogleMap.OnCameraChangeListener（）有三個攝像聽衆：

1.GoogleMap.OnCameraMoveStartedListener

2 .GoogleMap.OnCameraMoveListener

3.GoogleMap.OnCameraIdleListener

我想改變我下面的代碼與播放服務，映射到工作9.4.0版本的API，因爲我得到this.How NullPointerException異常我應該這樣做嗎？

googlemap.setOnCameraChangeListener(new OnCameraChangeListener() { 
// try{ 

@Override 
public void onCameraChange(CameraPosition arg0) { 

    LatLongDetails.user_latitude = arg0.target.latitude; 
    LatLongDetails.user_longitude = arg0.target.longitude; 
    if(LatLongDetails.user_latitude!=0||LatLongDetails.user_longitude!=0) 
    new ConversionTaskLatLonLoc(contextFix).execute(); 
    else{ 
      googlemap.clear(); 
      Toast.makeText(context,"error occured, please_wait", Toast.LENGTH_SHORT) 
        .show(); 
      user_latlongobj = findLocation(); 
      animatecamera(user_latlongobj); 
      getCabData(); 
     } 
    MapUtil.clearMarkers(googlemap); 
    MapUtil.dropPin(googlemap, arg0.target.latitude, 
      arg0.target.longitude, R.drawable.marker, 
      LoginDetails.Address).showInfoWindow(); 

    } 
}); 

這裏是logcat的

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.GoogleMap.setOnCameraChangeListener(com.google.android.gms.maps.GoogleMap$OnCameraChangeListener)' on a null object reference 
Authentication failed on the server. 
Google Maps Android API: Authorization failure. Please see https://developers.google.com/maps/documentation/android-api/start for how to correctly set up the map 
In the Google Developer Console (https://console.developers.google.com) 
Ensure that the "Google Maps Android API v2" is enabled. 
Ensure that the following Android Key exists: 
API Key: ************************************ 
Android Application (<cert_fingerprint>;<package_name>): ************** 

Answer 1

googlemap是null。在給googlemap賦值之前，不要致電setOnCameraChangeListener()。 onMapReady()將是一個可能的候選人，因爲我證明this sample app：

/*** 
    Copyright (c) 2012 CommonsWare, LLC 
    Licensed under the Apache License, Version 2.0 (the "License"); you may not 
    use this file except in compliance with the License. You may obtain a copy 
    of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless required 
    by applicable law or agreed to in writing, software distributed under the 
    License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS 
    OF ANY KIND, either express or implied. See the License for the specific 
    language governing permissions and limitations under the License. 

    From _The Busy Coder's Guide to Android Development_ 
    https://commonsware.com/Android 
*/ 

package com.commonsware.android.mapsv2.camera; 

import android.os.Bundle; 
import android.util.Log; 
import android.widget.Toast; 
import com.google.android.gms.maps.CameraUpdate; 
import com.google.android.gms.maps.CameraUpdateFactory; 
import com.google.android.gms.maps.GoogleMap; 
import com.google.android.gms.maps.GoogleMap.OnCameraIdleListener; 
import com.google.android.gms.maps.GoogleMap.OnCameraMoveCanceledListener; 
import com.google.android.gms.maps.GoogleMap.OnCameraMoveListener; 
import com.google.android.gms.maps.GoogleMap.OnCameraMoveStartedListener; 
import com.google.android.gms.maps.GoogleMap.OnInfoWindowClickListener; 
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.Marker; 
import com.google.android.gms.maps.model.MarkerOptions; 

public class MainActivity extends AbstractMapActivity implements 
    OnMapReadyCallback, OnInfoWindowClickListener, 
    OnCameraMoveStartedListener, 
    OnCameraMoveListener, 
    OnCameraMoveCanceledListener, 
    OnCameraIdleListener { 
    private boolean needsInit=false; 
    private GoogleMap map; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    if (readyToGo()) { 
     setContentView(R.layout.activity_main); 

     MapFragment mapFrag= 
      (MapFragment)getFragmentManager().findFragmentById(R.id.map); 

     if (savedInstanceState == null) { 
     needsInit=true; 
     } 

     mapFrag.getMapAsync(this); 
    } 
    } 

    @Override 
    public void onMapReady(final GoogleMap map) { 
    this.map=map; 

    if (needsInit) { 
     CameraUpdate center= 
      CameraUpdateFactory.newLatLng(new LatLng(40.76793169992044, 
                -73.98180484771729)); 
     CameraUpdate zoom=CameraUpdateFactory.zoomTo(15); 

     map.moveCamera(center); 
     map.animateCamera(zoom); 
    } 

    addMarker(map, 40.748963847316034, -73.96807193756104, 
       R.string.un, R.string.united_nations); 
    addMarker(map, 40.76866299974387, -73.98268461227417, 
       R.string.lincoln_center, 
       R.string.lincoln_center_snippet); 
    addMarker(map, 40.765136435316755, -73.97989511489868, 
       R.string.carnegie_hall, R.string.practice_x3); 
    addMarker(map, 40.70686417491799, -74.01572942733765, 
       R.string.downtown_club, R.string.heisman_trophy); 

    map.setInfoWindowAdapter(new PopupAdapter(getLayoutInflater())); 
    map.setOnInfoWindowClickListener(this); 

    map.setOnCameraMoveStartedListener(this); 
    map.setOnCameraMoveListener(this); 
    map.setOnCameraMoveCanceledListener(this); 
    map.setOnCameraIdleListener(this); 
    } 

    @Override 
    public void onInfoWindowClick(Marker marker) { 
    Toast.makeText(this, marker.getTitle(), Toast.LENGTH_LONG).show(); 
    } 

    @Override 
    public void onCameraIdle() { 
    CameraPosition position=map.getCameraPosition(); 

    Log.d("onCameraIdle", 
     String.format("lat: %f, lon: %f, zoom: %f, tilt: %f", 
     position.target.latitude, 
     position.target.longitude, position.zoom, 
     position.tilt)); 
    } 

    @Override 
    public void onCameraMoveCanceled() { 
    CameraPosition position=map.getCameraPosition(); 

    Log.d("onCameraMoveCanceled", 
     String.format("lat: %f, lon: %f, zoom: %f, tilt: %f", 
     position.target.latitude, 
     position.target.longitude, position.zoom, 
     position.tilt)); 
    } 

    @Override 
    public void onCameraMove() { 
    CameraPosition position=map.getCameraPosition(); 

    Log.d("onCameraMove", 
     String.format("lat: %f, lon: %f, zoom: %f, tilt: %f", 
     position.target.latitude, 
     position.target.longitude, position.zoom, 
     position.tilt)); 
    } 

    @Override 
    public void onCameraMoveStarted(int i) { 
    CameraPosition position=map.getCameraPosition(); 

    Log.d("onCameraMoveStarted", 
     String.format("lat: %f, lon: %f, zoom: %f, tilt: %f", 
     position.target.latitude, 
     position.target.longitude, position.zoom, 
     position.tilt)); 
    } 

    private void addMarker(GoogleMap map, double lat, double lon, 
         int title, int snippet) { 
    map.addMarker(new MarkerOptions().position(new LatLng(lat, lon)) 
     .title(getString(title)) 
     .snippet(getString(snippet))); 
    } 
}