android.database.CursorIndexOutOfBoundsException ...再次

Question

所以，我的应用程序在用户崩溃报告中出现此错误。以下是报告：

android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0 
at android.database.AbstractCursor.checkPosition(AbstractCursor.) 
at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.) 
at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50) 
at rs.androidaplikacije.zastaveigradovi.Kviz10Hard.nextQuestionGrad(Kviz10Hard.) 
at rs.androidaplikacije.zastaveigradovi.Kviz10Hard.access$1(Kviz10Hard.) 
at rs.androidaplikacije.zastaveigradovi.Kviz10Hard$2.run(Kviz10Hard.java:68) 
at android.os.Handler.handleCallback(Handler.) 
at android.os.Handler.dispatchMessage(Handler.java:92) 
at android.os.Looper.loop(Looper.) 
at android.app.ActivityThread.main(ActivityThread.) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.) 
at dalvik.system.NativeStart.main(Native Method) 

而这里提到的代码：

private void nextQuestionGrad() { 

    flag.setVisibility(View.GONE); 
    dodatnoPitanje.setVisibility(View.VISIBLE); 

    TestAdapter mDbHelper = new TestAdapter(this); 
    DataBaseHelper myDbHelper = new DataBaseHelper(this); 

    if(!myDbHelper.checkDataBase()){ 
     mDbHelper.createDatabase(); 
    } 

    try{ 

     mDbHelper.open(); 

     Cursor c = mDbHelper.getTestDataGradovi(mCurrentID); 

     List<Answer> labels = new ArrayList<Answer>(); 

     labels.add(new Answer(c.getString(2), true)); 
     labels.add(new Answer(c.getString(3), false)); 
     labels.add(new Answer(c.getString(4), false)); 
     labels.add(new Answer(c.getString(5), false)); 

     tacanOdg = c.getString(2); 

     Collections.shuffle(labels); 

     dodatnoPitanje.setText(c.getString(1)); 

     bOdgovor1.setText(labels.get(0).option); 
     bOdgovor1.setTag(labels.get(0)); 
     bOdgovor1.setOnClickListener(clickListenerGrad); 

     bOdgovor2.setText(labels.get(1).option); 
     bOdgovor2.setTag(labels.get(1)); 
     bOdgovor2.setOnClickListener(clickListenerGrad); 

     bOdgovor3.setText(labels.get(2).option); 
     bOdgovor3.setTag(labels.get(2)); 
     bOdgovor3.setOnClickListener(clickListenerGrad); 

     bOdgovor4.setText(labels.get(3).option); 
     bOdgovor4.setTag(labels.get(3)); 
     bOdgovor4.setOnClickListener(clickListenerGrad); 

     score.setText("Score: " + brojacTacnihOdgovora); 

    }finally{ 
     mDbHelper.close(); 
    } 
} 

及部分我的适配器类的我使用这个类：

public Cursor getTestDataGradovi(long id){ 
    try{ 
     String sql ="SELECT * FROM tblGradovi WHERE _ID = " + id; 

     Cursor c = mDb.rawQuery(sql, null); 
     if (c!=null){ 
      c.moveToNext(); 
     } 
     return c; 
    }catch (SQLException mSQLException){ 
     Log.e(TAG, "getTestData >>"+ mSQLException.toString()); 
     throw mSQLException; 
    } 
} 

有人能告诉我在哪里问题？错误行（Kviz10Hard。）在这里：

labels.add(new Answer(c.getString(2), true)); 

Answer 1

在尝试从Cursor对象获取任何数据之前，如果光标只包含一个值，则需要迭代结果或获取第一个数据。例如所有的结果之间的迭代，你应该做这样的事情：

String sql = "SELECT * FROM myTable"; 
Cursor cursor = mDbHelper.rawQuery(sql, null); 
if(cursor != null){ 
    if(cursor.getCount() > 0){ 
     for(cursor.move(0);cursor.moveToNext();cursor.isAfterLast()){ 
      // get your data here 
     } 
    } 
    cursor.close(); // close your cursor when you don't need it anymore 
} 

或另一种方式来做到这一点：

String sql = "SELECT * FROM myTable"; 
Cursor cursor = mDbHelper.rawQuery(sql, null); 
if(cursor != null){ 
    if(cursor.getCount() > 0){ 
     do { 
      // get value 
     } while(cursor.moveToNext()); 
    } 
    cursor.close(); // close your cursor when you don't need it anymore 
} 

，或者如果你是相当肯定的结果应该是只有一个对象这取决于你的SQL语句，你应该从你的Cursor访问这样的事之前调用cursor.moveToFirst();：

String sql = "SELECT * FROM myTable"; 
Cursor cursor = mDbHelper.rawQuery(sql, null); 
if(cursor != null){ 
    cursor.moveToFirst(); 
    String myString = cursor.getString(cursor.getColumnIndex("title")); 
    cursor.close(); // close your cursor when you don't need it anymore 
} 

编辑：

如果你真的想在你的数据库类来创建这样的功能，我会做这样的事情：

public static Cursor getUserTitles(int userId){ 
     String sql = "SELECT * FROM myTable WHERE userId=?"; 
     return mDbHelper.rawQuery(sql, new String[]{Integer.toString(userId)}); 
} 

第二个编辑：

更改getTestDataGradovi到：

public Cursor getTestDataGradovi(long id){ 
    String sql ="SELECT * FROM tblGradovi WHERE _ID=?"; 
    return mDb.rawQuery(sql, new String[]{Integer.toString(id)}); 
} 

and add c.moveToFirst();，aft呃Cursor c = mDbHelper.getTestDataGradovi(mCurrentID);

Answer 2

您不检查游标是否包含任何结果。你需要检查返回值c.moveToNext()，或检查c.getCount()或类似的东西。