Question

情况：我从服务器获得了包含用户播放列表的JSONObject。我想在ListView中显示这些数据，在我的测试用例中有288个音频文件。 JSON被正确解析，大小等于288.我创建了一个帮助类，并使用其对象对ArrayList进行参数化。问题：我的ListView中只有288个项目但是正确的条目艺术家 - 标题上升到索引13（不知道原因）然后他们得到重复。所以我在列表中没有288个不同的条目，但我只有14个条目重复到列表结尾。

更新：我删除了if语句并解决了问题，但RAM消耗增加了3MB。有什么优化建议吗？

   public class AudioList extends ListActivity {

private ListView lv;
private JSONObject usersPlaylist, singleJSONItem;
private JSONArray responseJSONArray;
private SharedPreferences prefs;
private PlaylistItem audioList;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_audio_list);
    init();

    ArrayList<PlaylistItem> playlist = new ArrayList<PlaylistItem>();
    try {
        usersPlaylist = Utils.retrieveJsonObjectFromUrl(new URL(
                APP_CONSTANTS.REQUEST_AUDIO_LIST(prefs)), this);
        responseJSONArray = usersPlaylist.getJSONArray("response");

        for (int i = 0; i < responseJSONArray.length(); i++) {
            singleJSONItem = responseJSONArray.getJSONObject(i);
            audioList = new PlaylistItem(singleJSONItem);
            playlist.add(audioList); 
        }

        Toast.makeText(getApplicationContext(),
                Integer.toString(playlist.size()), Toast.LENGTH_LONG)
                .show(); //there are 288 entries, JSONArray parsed correctly

    } catch (MalformedURLException e) {

        e.printStackTrace();
    } catch (JSONException e) {

        e.printStackTrace();
    } catch (IOException e) {

        e.printStackTrace();
    }

    AudioListAdapter adapter = new AudioListAdapter(this,
            R.layout.playlist_item, playlist);
    lv.setAdapter(adapter);

}

private void init() {
    lv = getListView();
    lv.setTranscriptMode(0x00000000);
    lv.setDividerHeight(1);
    lv.setSmoothScrollbarEnabled(true);
    prefs = PreferenceManager.getDefaultSharedPreferences(this);

}

PlayListItem类：

     public class PlaylistItem {

private String artist, title;
private JSONObject obj;

public PlaylistItem(JSONObject obj) {
    this.obj = obj;
}
public PlaylistItem(){

}

public String getArtist() {
    try {
        artist = obj.getString("artist");
    } catch (JSONException e) {

        e.printStackTrace();
    }
    return artist;

}

public String getTitle() {
    try {
        title = obj.getString("title");
    } catch (JSONException e) {

        e.printStackTrace();
    }
    return title;
}
    }

适配器：

     public class AudioListAdapter extends ArrayAdapter<PlaylistItem> {

private Context context;
private int layoutResourceId;
private PlaylistItem aud;
private ArrayList<PlaylistItem> data = null;

public AudioListAdapter(Context context, int layoutResourceId,
        ArrayList<PlaylistItem> data) {
    super(context, layoutResourceId, data);
    this.layoutResourceId = layoutResourceId;
    this.context = context;
    this.data = data;

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View row = convertView;
    ViewHolder holder = new ViewHolder();
    aud = data.get(position);
            //it's giving a CORRECT position if I hardcode the index, like data.get(99);
    if (row == null) {

        LayoutInflater inflater = ((Activity) context).getLayoutInflater();
        row = inflater.inflate(layoutResourceId, parent, false);
        holder.play = (Button) row.findViewById(R.id.btn_list_play);
        holder.imgSaved = (ImageView) row
                .findViewById(R.id.img_list_audio_saved);
        holder.tvArtist = (TextView) row
                .findViewById(R.id.tvListItemArtist);
        holder.tvTitle = (TextView) row.findViewById(R.id.tvListItemSong);

        holder.tvArtist.setText(aud.getArtist());
        holder.tvTitle.setText(aud.getTitle());

    }

    return row;
}

static class ViewHolder {
    Button play;
    ImageView imgSaved;
    TextView tvArtist, tvTitle;

}

    }

Answer 1

在getView方法中，如果它是循环使用的，则不会再次填充View。因此，一旦您在屏幕外滚动它将开始显示旧的。您也没有设置/检索ViewHolder。请尝试以下实施（未经测试）。

@Override
public View getView(int position, View convertView, ViewGroup parent) {
   View row = convertView;
   ViewHolder holder = null;
   aud = data.get(position);
        //it's giving a CORRECT position if I hardcode the index, like data.get(99);
   if (row == null) {
       holder = new ViewHolder();
       LayoutInflater inflater = ((Activity) context).getLayoutInflater();
       row = inflater.inflate(layoutResourceId, parent, false);
       holder.play = (Button) row.findViewById(R.id.btn_list_play);
       holder.imgSaved = (ImageView) row
            .findViewById(R.id.img_list_audio_saved);
       holder.tvArtist = (TextView) row
            .findViewById(R.id.tvListItemArtist);
       holder.tvTitle = (TextView) row.findViewById(R.id.tvListItemSong);          
       row.setTag(holder);
} else {
    holder = (ViewHolder)row.getTag();
}
holder.tvArtist.setText(aud.getArtist());
holder.tvTitle.setText(aud.getTitle());

return row;
}

Answer 2

如果您要删除此行：

 View row = convertView;

每次都给视图充气，然后这个问题就会消失。我这样做了很多次，如下所述：

How to save state of changed ImageView in Listview row, after it' has disappeared from screen?

实际上我不知道为什么会这样，因为建议使用convertView。

<强>更新

试试这个：

@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row;
ViewHolder holder = new ViewHolder();
LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
row = inflater.inflate(layoutResourceId, parent, false);
holder.play = (Button) row.findViewById(R.id.btn_list_play);
holder.imgSaved = (ImageView) row.findViewById(R.id.img_list_audio_saved);
holder.tvArtist = (TextView) row.findViewById(R.id.tvListItemArtist);
holder.tvTitle = (TextView) row.findViewById(R.id.tvListItemSong);
holder.tvArtist.setText(aud.getArtist());
holder.tvTitle.setText(aud.getTitle());

return row;

}

Answer 3

我在你的getView方法中做了一些修改。放置并检查它。

  @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View row = convertView;
            ViewHolder holder;
            aud = data.get(position);
                    //it's giving a CORRECT position if I hardcode the index, like data.get(99);
            if (row == null) {
                holder = new ViewHolder();
                LayoutInflater inflater = ((Activity) context).getLayoutInflater();
                row = inflater.inflate(layoutResourceId, parent, false);
                holder.play = (Button) row.findViewById(R.id.btn_list_play);
                holder.imgSaved = (ImageView) row.findViewById(R.id.img_list_audio_saved);
                holder.tvArtist = (TextView) row .findViewById(R.id.tvListItemArtist);
                holder.tvTitle = (TextView) row.findViewById(R.id.tvListItemSong);
                row.setTag(holder);
        }
    else
    {
                    holder = (ViewHolder ) row.getTag();

    }
                holder.tvArtist.setText(aud.getArtist());
                holder.tvTitle.setText(aud.getTitle());



            return row;
        }

Answer 4

      if (convertView == null)// if null

       {
        convertView = mInflater.inflate(R.layout.list, null);//inflate view
       } else 
       {
        holder = (ViewHolder) convertView.getTag();// set tag to holder.
       }

进行这些更改。

android - 使用来自JSONArray的数据填充ListView

4 个答案: