零地圖組件在Android中初始化時的指針

Question

我有一個應用程序，我一直在努力。主要活動顯示使用Android版Google地圖類（v2）的地圖。有時，並不總是，當我啓動我的應用時，我會得到一個空指針。上次發生這種情況時，一天後停止發生，代碼沒有任何變化。我預感到地圖對象在查看logcat（下面發佈）後仍然不可用。

所以我看了這個頁面：https://developers.google.com/maps/documentation/android/map（驗證地圖可用性部分），並且我已經確定地圖對象在onCreate中不爲null。

由於此問題是間歇性的，我只能猜測它與Google服務有關。我最近強制停止並清除了Google服務框架應用程序的數據，以嘗試更新到4.2.2（起訴我）。任何想法 - 有沒有人聽說過這個，還是有人知道如何解決它？

編輯：此代碼現在再次工作，完全如您在這裏看到的。我沒有改變任何東西。

所以我的問題是：什麼會導致這種行爲？我正在使用直接來自Google Maps for Android v2文檔的代碼檢查地圖對象（下面第142行的NPE）是否在onCreate（），onStart（）和onResume（）中爲null。

列入的onCreate（），在onStart（）和的onResume（）不應該允許這種...：

// 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

我建議你像下面一樣修改你的代碼;

@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)); 

我認爲在onStart（）中添加toomany方法並不合適。