所有元素都被 hashmap 的数组列表中的最后一个元素替换 [英] All elements are replaced by last element in an arraylist of hashmap

问题描述

我的价值观是

问题Q-id
Q1 1
Q2 2
...等等

Question Q-id
Q1 1
Q2 2
...and so on

我想通过调用一个函数来检索它们.所以我使用了一个 HashMaps 的数组列表，如下所示..

I want to retrieve them by calling a function. So i used an arraylist of HashMaps as follows..

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 显示在单独提取时成功检索了所有问题(如 Log.i 语句所示)，但是当我在最后运行以下循环时，所有元素都被最后提取的问题替换.非常感谢任何帮助.

Now the Logcat shows that all questions are retrieved successfully at the time of individual fetch (as shown by the Log.i statement) but whe i run the following loop at the end all the elements are replaced by the last fetched question. Any help is much appreciated.

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

推荐答案

调用 add 方法时，只会添加对对象的引用.所以下次修改对象时，引用指向修改后的对象，不保留对象的旧状态.

When you call the add method, only the reference to the object is added. So next time you modify the object, the reference refers to the modified object and the old state of the object is not retained.

在您的情况下，每次要将新对象添加到 List 时，您都必须创建新对象:

In your case, you will have to create new objects every time you want to add them to the 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());
     }

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