NullPointerException异常SQLiteAssetHelper

Question

我想从我的数据库中获取信息列表并将其显示到自定义列表视图中。我已经有了我的DatabaseHelper，Fragment和Adapter安装程序。下面是我收到的错误：

04-29 13:36:52.539: E/AndroidRuntime(8135): FATAL EXCEPTION: main 
04-29 13:36:52.539: E/AndroidRuntime(8135): java.lang.NullPointerException 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:110) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:130) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at com.rcd.mypr.Workouts.WorkoutsDatabaseHelper.<init>(WorkoutsDatabaseHelper.java:35) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at com.rcd.mypr.Workouts.WorkoutsFragment.onCreateView(WorkoutsFragment.java:36) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:828) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1032) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.app.BackStackRecord.run(BackStackRecord.java:622) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1382) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.app.FragmentManagerImpl$1.run(FragmentManager.java:426) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.os.Handler.handleCallback(Handler.java:605) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.os.Handler.dispatchMessage(Handler.java:92) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.os.Looper.loop(Looper.java:137) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at android.app.ActivityThread.main(ActivityThread.java:4424) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at java.lang.reflect.Method.invoke(Method.java:511) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
04-29 13:36:52.539: E/AndroidRuntime(8135):  at dalvik.system.NativeStart.main(Native Method) 

这里是我的WorkoutsDatabaseHelper.java

package com.rcd.mypr.Workouts; 

import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 

import com.readystatesoftware.sqliteasset.SQLiteAssetHelper; 

public class WorkoutsDatabaseHelper extends SQLiteAssetHelper { 


    // All Static variables 
    // Database Version 
    private static final int DATABASE_VERSION = 1; 

    // Database Name 
    private static final String DATABASE_NAME = "workoutsDatabase.sqlite"; 
    private static final String WORKOUTS_TABLE = "workouts"; 

    // Workouts Table Columns names 
    private static final String KEY_ID = "_id"; 
    private static final String KEY_WORKOUT_NAME = "workout_name"; 
    private static final String KEY_HERO_LAST_NAME = "hero_last_name"; 
    private static final String KEY_HERO_FIRST_NAME = "hero_first_name"; 
    private static final String KEY_HERO_MIDDLE_NAME = "hero_middle_name"; 
    private static final String KEY_HERO_DESCRIPTION = "hero_description"; 
    private static final String KEY_DATE_ADDED = "date_added"; 
    private static final String KEY_WORKOUT = "workout"; 
    private static final String KEY_MEASUREMENT = "measurement"; 
    private static final String KEY_PHOTO = "photo"; 



    public WorkoutsDatabaseHelper(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    public Cursor getWorkoutNames() { 

     SQLiteDatabase db = getReadableDatabase(); 
     Cursor cursor = db.query(WORKOUTS_TABLE, new String[] {"_id", "workout_name"}, null, null, null, 
       null, KEY_WORKOUT_NAME + " ASC"); 
     return cursor; 

    } 


} 

，最后，这是我WorkoutsFragment.java

package com.rcd.mypr.Workouts; 

import android.app.Fragment; 
import android.content.Context; 
import android.database.Cursor; 
import android.os.Bundle; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ListView; 

import com.rcd.mypr.R; 


public class WorkoutsFragment extends Fragment { 

    WorkoutsDatabaseHelper db; 
    SimpleCursorAdapter adapter; 
    ListView listContent; 
    private int position; 
    Cursor cursor; 
    private Context mContext; 
    WorkoutsAdapter workoutsAdapter; 

    public WorkoutsFragment(){} 


    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 

     db = new WorkoutsDatabaseHelper(mContext); 
     mContext = getActivity(); 
     View rootView = inflater.inflate(R.layout.activity_workouts, container, false); 

     listContent = (ListView) rootView.findViewById(android.R.id.list); 

     // Create the Adapter 
     workoutsAdapter = new WorkoutsAdapter(mContext, cursor); 

     // Set the adapter to ListView 
     listContent.setAdapter(workoutsAdapter); 
     return rootView; 
    } 



    private void initViews(){ 
     //Typeface tf = Typeface.createFromAsset(mContext.getAssets(),"Roboto-Light.ttf"); 
    } 

    private void addItemsToList(){ 
     Cursor cursor = db.getWorkoutNames(); 
     Log.d("history.java", "finished Cursor cursor = db.getAllLogs();"); 
     String[] from = {"_id", "workouts_name"}; 
     int[] to = {R.id.tv_id, R.id.tv_label}; 
     adapter = new SimpleCursorAdapter(mContext, R.layout.single_item, cursor, from, to, 0); 
     listContent.setAdapter(adapter); 

    } 

    public void onResume(){ 
     super.onResume(); 
     workoutsAdapter = new WorkoutsAdapter(mContext, cursor); 
     listContent.setAdapter(workoutsAdapter); 
    } 


} 

如果有其他任何你需要看看请让我知道。

Answer 1

错误出现在您的Fragment的onCreateView()-方法中。 您使用nullContext初始化您的WorkoutsDatabaseHelper。

db = new WorkoutsDatabaseHelper(mContext); 
    mContext = getActivity(); 

开关这两条线，然后再试一次......