android ListView简单的适配器，重复项目 [英] android ListView Simple Adapter, item repeating

问题描述

我创建了一个自定义的 ListView ，并在java中用 SimpleAdapter填充了 ListView / code>。这是我的代码：



  setContentView（R.layout.activity_my）; 
 list =（ListView）findViewById（R.id.lvList）; 
 
 itemList = new ArrayList< HashMap< String，String>>（）; 
 itemMap = new HashMap< String，String>（）; 
 
 for（int i = 0; i< songs.length; i ++）{
 itemMap.put（song，songs [i]）; 
 itemMap.put（artist，artists [i]）; 
 System.out.println（歌曲[i] ++ artists [i]）; 
 itemList.add（itemMap）; 
} 
 
 SimpleAdapter adapter = new SimpleAdapter（this，itemList，
 android.R.layout.simple_list_item_2，new String [] {song，
artist }，new int [] {android.R.id.text1，
 android.R.id.text2}）; 
 list.setAdapter（adapter）; 
  

现在我创建了两个字符串数组 Artist分别放入 HashMap 中，然后将 HashMap 放入 ArrayList 称为 itemList 。之后，我在参数中设置了默认列表项ID的适配器。

我遇到的问题是当我运行应用程序时，列表视图仅显示字符串数组的最后一项和子项重复。这是供参考的图片。
我的ListView

<我想知道为什么会发生这种情况。我尝试在（）循环中将 itemList.add（itemMap）; 放在之外，但它仍然不起作用。帮助将真正赞赏与一个适当的解释，因为我有点新的这一点。谢谢！

解决方案

您可以通过重新创建您的 itemMap 对象在每一次迭代。尝试以下方法。

  itemMap = new HashMap< String，String>（）; 
 
 for（int i = 0; i< songs.length; i ++）{
 itemMap.put（song，songs [i]）; 
 itemMap.put（artist，artists [i]）; 
 System.out.println（歌曲[i] ++ artists [i]）; 
 itemList.add（itemMap）; 
 
 $ / code> 

更改为



  for（int i = 0; i< songs.length; i ++）{
 itemMap = new HashMap< String，String>（）; 
 itemMap.put（song，songs [i]）; 
 itemMap.put（artist，artists [i]）; 
 System.out.println（歌曲[i] ++ artists [i]）; 
 itemList.add（itemMap）; 
 
  

解释：



请参阅此处。注意 HashMap 是一个键 值对，这意味着它会为钥匙存储一些价值。所以 HashMap 将不允许重复键。从你的代码中，你已经添加了歌曲和艺术家的值。所以你不能再添加这些键的值。但是 itemlist 在每次迭代中添加 itemMap 。这就是重复相同记录的列表的原因。为了避免这个问题，只需重新初始化 itemMap 对象。

我希望这会对你有帮助。

I created a custom ListView and in java filled that ListView with a SimpleAdapter. Here's my code:

setContentView(R.layout.activity_my);
list = (ListView) findViewById(R.id.lvList);

itemList = new ArrayList<HashMap<String, String>>();
itemMap = new HashMap<String, String>();

for (int i = 0; i < songs.length; i++) {
    itemMap.put("song", songs[i]);
    itemMap.put("artist", artists[i]);
    System.out.println(songs[i] + "     " + artists[i]);
    itemList.add(itemMap);
}

SimpleAdapter adapter = new SimpleAdapter(this, itemList,
            android.R.layout.simple_list_item_2, new String[] {"song",
                    "artist"}, new int[] { android.R.id.text1,
                    android.R.id.text2 });
list.setAdapter(adapter);

Now I created two String Arrays Song and Artist respectively and put them in a HashMap and then put the HashMap in a ArrayList called itemList. After that i set up the adapter with the default list item id's in the parameter.

The problem I am facing is that when i run the application, the list view shows only the last item and subItem of the String Arrays repeatedly. Here's the image for reference. My ListView

I'd like to know why this is happening. I tried putting the itemList.add(itemMap); outside the for() loop but it still didn't work. Help would really be appreciated with a proper explanation, cause i'm kinda new to this. Thank You!

解决方案

You can achieve this by recreating your itemMap object at every iteration. Try the following way.

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

for (int i = 0; i < songs.length; i++) {
    itemMap.put("song", songs[i]);
    itemMap.put("artist", artists[i]);
    System.out.println(songs[i] + "     " + artists[i]);
    itemList.add(itemMap);
}

Change this to

for (int i = 0; i < songs.length; i++) {
    itemMap = new HashMap<String, String>();
    itemMap.put("song", songs[i]);
    itemMap.put("artist", artists[i]);
    System.out.println(songs[i] + "     " + artists[i]);
    itemList.add(itemMap);
}

Explaination:

Refer here. Note HashMap is a key value pair which means it will store some value for a key. So HashMap will not allow duplicate key. From your code already youe have added the value for song and artist. So you can not add the value for these keys again. But the itemlist add the itemMap at every iteration. That is why the list repeating the same record. To avoid this problem simply re instantiate the itemMap object.

I hope this will help you.

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