SQLite中的Android

Question

將數據添加到容器類我有一個contailer類ServiceMeasureCollection：

import java.util.ArrayList; 

public class ServiceMeasureCollection { 
public String service_id=""; 
public String service_type=""; 
public String service_measure=""; 

public static ArrayList<ServiceMeasureCollection> data_arr=null; 
public ServiceMeasureCollection(String service_id,String service_type, String service_measure){ 

     this.service_id=service_id; 
     this.service_type=service_type; 
     this.service_measure=service_measure; 
    } 
} 

我想從一個ArrayList調用這個類並填寫qith sqlite的數據如下：

public ArrayList<ServiceMeasureCollection> getServiceProviderServices() { 
    ServiceMeasureCollection.data_arr = new ArrayList<ServiceMeasureCollection>(); 

    Log.d("test", "testing if getServProv Services works "); 
    String selectQuery = "SELECT * FROM " + TABLE_SERVICEPROVSERVICE; 

    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 
    Log.d(TAG, "testing if getServProv Services works "); 
    // Move to first row 
    cursor.moveToFirst(); 

     if (cursor.getCount() > 0) { 
      do { 
       ServiceMeasureCollection.data_arr.add(new ServiceMeasureCollection(cursor.getString(0), 
       cursor.getString(8),cursor.getString(1))); 

      } while (cursor.moveToNext()); 
     } 

    cursor.close(); 
    db.close(); 
    // return user 
    Log.d(TAG, "Fetching user from Sqlite: " +ServiceMeasureCollection.data_arr.toString()); 

    return ServiceMeasureCollection.data_arr; 
} 

每次我嘗試通過我的主叫db.getServiceProviderServices()我得到一個空指針異常。我猜這是因爲我初始化了data_arr=Null。 有誰知道如何解決這個問題或真正的問題是什麼？

堆棧跟蹤：

E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: de.monobono.monobonoapp, PID: 4458 
        java.lang.NullPointerException 
         at de.monobono.monobonoapp.activity.ProviderServiceListFragment.onViewCreated(ProviderServiceListFragment.java:78) 
         at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086) 
         at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252) 
         at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742) 
         at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617) 
         at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517) 
         at android.os.Handler.handleCallback(Handler.java:733) 
         at android.os.Handler.dispatchMessage(Handler.java:95) 
         at android.os.Looper.loop(Looper.java:136) 
         at android.app.ActivityThread.main(ActivityThread.java:5147) 
         at java.lang.reflect.Method.invokeNative(Native Method) 
         at java.lang.reflect.Method.invoke(Method.java:515) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:611) 
         at dalvik.system.NativeStart.main(Native Method) 

編輯：

public class ProviderServiceListFragment extends Fragment { 

View myView; 
public String stampid; 
private ListView listView; 
private ListView listView2; 
private ListView listView3; 
public TextView dr_name; 
private ProgressDialog pDialog; 
private SQLiteHandler connection; 
private SQLiteHandler db; 
private ServiceMeasureAdapter list_adapter; 
private ListView lv_android; 

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    myView = inflater.inflate(R.layout.service_measure_list_section, container, 
false); 
     return myView; 

} 

@Override 
public void onViewCreated(View view, Bundle savedInstanceState) { 
    stampid = getArguments().getString("stampID"); 
    super.onViewCreated(view, savedInstanceState); 

    db.getServiceProviderServices(); 

} } 

Answer 1

你的成員變量private SQLiteHandler db是由時間onViewCreated被稱爲空。這是造成你的NullPointerException。您必須添加這樣的事情是你的片段

db = new SQLiteHandler(/*Required parameters*/);