android-用来自JSONArray的数据填充ListView

Question

Situation: I'm getting a JSONObject containing user's playlist from the server. I want to display this data in a ListView , there are 288 audio files in my test case. The JSON is parsed correctly, the size equals to 288. I created a help class and parametrized the ArrayList with its Objects. The problem: there're exactly 288 items in my ListView BUT the correct entries Artist - Title go up to index 13 (don't know why) and then they get repeated . So I don't have 288 different entries in the List, but I have only 14 entries which are repeated until the end of the List.

UPDATE: I removed the if statement and it solved the issue but RAM consumption has increased by 3MB. Any suggestions for optimizing?

   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);

}

The PlayListItem class:

     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;
}
    }

The adapter:

     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

In getView method you are not populating the View again if it's a recycled one. Therefore once you scroll outside the screen it will start displaying the old ones. You are also not setting/retrieving the ViewHolder. Please try the following implementation (not tested).

@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

If you will remove this line:

 View row = convertView;

and inflate the view every time, then this problem will go away. I did as well encountered this affect a couple of times as described here:

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

actualy i dont know why this happens because using the convertView is recommended.

Update:

try this one:

@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

I have done some modifications in your getView method.Replace it and check it.

  @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.
       }

Make those changes.