所有元素都被hashmap的arraylist中的last元素替换

Question

我有价值观

问题Q-id
Q1 1
Q2 2
......依此类推

我想通过调用函数来检索它们.所以我使用了HashMaps的arraylist如下..

public ArrayList<HashMap<String,String>> getAllQuestions(Integer id)
 {
     try
     {
         HashMap<String,String> QuesList = new HashMap<String,String>();
         ArrayList<HashMap<String, String>> QuestionArrayList = new ArrayList<HashMap<String, String>>();
         // Select All Query
         String selectQuery = <some query here>;

          cursor = mDb.rawQuery(selectQuery, null);

         // looping through all rows and adding to list
         if (cursor.moveToFirst()) 
         {
             do 
             {

                 QuesList.put("ques_id", cursor.getString(2));
                 QuesList.put("ques_text", cursor.getString(8));
                 QuestionArrayList.add(QuesList);
                 Log.i("ques",cursor.getString(8) );
             } while (cursor.moveToNext());
         }


         Log.i("check"," Ques list returned");
         return QuestionArrayList;

     }
     catch (SQLException mSQLException) 
     {
         Log.e(TAG, "getTestData >>"+ mSQLException.toString());
         throw mSQLException;
     }
 }

现在,Logcat显示在单个提取时成功检索所有问题(如Log.i语句所示),但是当我在结束时运行以下循环时,所有元素都被最后提取的问题替换.任何帮助深表感谢.

   for(HashMap<String, String> t : QuesList )
    {
        Log.d("out there", "count" + t.getString());
        Log.i("mapping....",t.get("ques_id"));
     }

Answer 1

调用add方法时,仅添加对对象的引用.因此,下次修改对象时,引用会引用已修改的对象,并且不会保留对象的旧状态.

在您的情况下,每次要将它们添加到以下内容时,您都必须创建新对象List:

     // looping through all rows and adding to list
     if (cursor.moveToFirst()) 
     {
         do 
         {
             //Create a new object instance of the Map
             HashMap<String,String> QuesList = new HashMap<String,String>();

             QuesList.put("ques_id", cursor.getString(2));
             QuesList.put("ques_text", cursor.getString(8));
             QuestionArrayList.add(QuesList);
             Log.i("ques",cursor.getString(8) );
         } while (cursor.moveToNext());
     }