如何将HashMap添加到ArrayList

Question

有人可以告诉我为什么下面的代码用ArrayList中的最新条目覆盖ArrayList中的每个元素？或者如何正确地将新的hashmap元素添加到我的ArrayList中？

ArrayList<HashMap<String, String>> prodArrayList = new ArrayList<HashMap<String, String>>();

HashMap<String, String> prodHashMap = new HashMap<String, String>();

public void addProd(View ap)
{
    // test arraylist of hashmaps
    prodHashMap.put("prod", tvProd.getText().toString());

    prodArrayList.add(prodHashMap);

    tvProd.setText("");

    // check data ///

    Log.e("myLog","Data prodArrayList in ADD Method Size = "+prodArrayList.size());

    for(int i=0; i< prodArrayList.size();i++)
    {
         Log.e("myLog","Data prodArrayList in ADD Method = "+prodArrayList.get(i).toString());
    }
}

Answer 1

问题:

prodHashMap.put("prod", tvProd.getText().toString());

每次向arraylist添加元素时都使用相同的键,并HashMap对其值进行相同的引用.

解:

HashMap每次要将其添加到其中时创建一个新实例,ArrayList以避免在调用时更改其值addProd

public void addProd(View ap)
{
    // test arraylist of hashmaps
    HashMap<String, String> prodHashMap = new HashMap<String, String>();
    prodHashMap.put("prod", tvProd.getText().toString());

    prodArrayList.add(prodHashMap);

    tvProd.setText("");

    // check data ///

    Log.e("myLog","Data prodArrayList in ADD Method Size = "+prodArrayList.size());

    for(int i=0; i< prodArrayList.size();i++)
    {
         Log.e("myLog","Data prodArrayList in ADD Method = "+prodArrayList.get(i).toString());
    }
}