零地图组件在Android中初始化时的指针

Question

我有一个应用程序，我一直在努力。主要活动显示使用Android版Google地图类（v2）的地图。有时，并不总是，当我启动我的应用时，我会得到一个空指针。上次发生这种情况时，一天后停止发生，代码没有任何变化。我预感到地图对象在查看logcat（下面发布）后仍然不可用。

所以我看了这个页面：https://developers.google.com/maps/documentation/android/map（验证地图可用性部分），并且我已经确定地图对象在onCreate中不为null。

由于此问题是间歇性的，我只能猜测它与Google服务有关。我最近强制停止并清除了Google服务框架应用程序的数据，以尝试更新到4.2.2（起诉我）。任何想法 - 有没有人听说过这个，还是有人知道如何解决它？

编辑：此代码现在再次工作，完全如您在这里看到的。我没有改变任何东西。

所以我的问题是：什么会导致这种行为？我正在使用直接来自Google Maps for Android v2文档的代码检查地图对象（下面第142行的NPE）是否在onCreate（），onStart（）和onResume（）中为null。

列入的onCreate（），在onStart（）和的onResume（）不应该允许这种...：

// Do a null check to confirm that we have not already instantiated the map. 
    if (mMap == null) { 
    mMap = ((MapFragment) getFragmentManager().findFragmentById(R.id.mainMap)) 
         .getMap(); 
    // Check if we were successful in obtaining the map. 
    if (mMap != null) { 
     // The Map is verified. It is now safe to manipulate the map. 

logcat的：

02-14 13:33:03.190: E/AndroidRuntime(5448): Caused by: java.lang.NullPointerException 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at maps.ar.b.a(Unknown Source) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at maps.y.h.a(Unknown Source) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at maps.y.au.a(Unknown Source) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at maps.y.ae.moveCamera(Unknown Source) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at com.google.android.gms.maps.internal.IGoogleMapDelegate$Stub.onTransact(IGoogleMapDelegate.java:83) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at android.os.Binder.transact(Binder.java:310) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at com.google.android.gms.maps.internal.IGoogleMapDelegate$a$a.moveCamera(Unknown Source) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at com.google.android.gms.maps.GoogleMap.moveCamera(Unknown Source) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at com.tyler.ioio.MainActivity.onStart(MainActivity.java:142) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1164) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at android.app.Activity.performStart(Activity.java:5114) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2153) 
02-14 13:33:03.190: E/AndroidRuntime(5448):  ... 11 more 

MainActivity：

protected void onStart() { 
    super.onStart(); 

    // This verification should be done during onStart() because the system 
    // calls this method when the user returns to the activity, which 
    // ensures the desired location provider is enabled each time the 
    // activity resumes from the stopped state. 
    mLocMan = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 

    final boolean gpsEnabled = mLocMan.isProviderEnabled(LocationManager.GPS_PROVIDER); 

    if (!gpsEnabled) { 
     new EnableGpsDialogFragment().show(getFragmentManager(), 
       "enableGpsDialog"); 
    } 

    // Optimized code to go to location as fast as possible 
    Location firstLoc = mLocMan.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
    updateNewFix(getBetterLocation(firstLoc, currentLoc)); 
    // THIS IS LINE 142 : FORCE CLOSES 
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(currentLatLng, DEFAULT_ZOOM)); 
    mMap.setOnMapClickListener(this); 

Answer 1

我建议你像下面一样修改你的代码;

@Override 
protected void onCreate(Bundle savedInstanceState) { 

mMap.setOnMapClickListener(this); 

} 

protected void onStart() { 
    super.onStart(); 

// This verification should be done during onStart() because the system 
// calls this method when the user returns to the activity, which 
// ensures the desired location provider is enabled each time the 
// activity resumes from the stopped state. 
    mLocMan = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 

    final boolean gpsEnabled = mLocMan.isProviderEnabled(LocationManager.GPS_PROVIDER); 

    if (!gpsEnabled) { 
     new EnableGpsDialogFragment().show(getFragmentManager(), 
      "enableGpsDialog"); 
    } 


@Override 
protected void onResume() { 
    super.onResume(); 
    setup(); 

private void setup() { 

// Optimized code to go to location as fast as possible 
Location firstLoc = mLocMan.getLastKnownLocation(LocationManager.GPS_PROVIDER); 
updateNewFix(getBetterLocation(firstLoc, currentLoc)); 
// THIS IS LINE 142 : FORCE CLOSES 

mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(currentLatLng, DEFAULT_ZOOM)); 

我认为在onStart（）中添加toomany方法并不合适。