创建列表视图适配器没有开始传递数组 [英] Creating an adapter for listview without passing an array initially

问题描述

我有AA客户适配器（ SongsAdapter ）扩展 ArrayAdapter ，它包含<$ C $的数组C>歌曲的对象。在我片段 onCreateView 方法，我想初始化该适配器。

 适配器=新SongsAdapter（的getContext（），arrayOfSongs）;
 

问题是， arrayOfSongs 最初为null。用户应搜索数据库的iTunes上的歌曲，当我得到回应，我解析JSON并创建歌曲对象，然后将它们添加到我的适配器

  adapter.addAll（听歌）;
 

然后

  adapter.notifyDataSetChanged（）;
 

但我发现了一个异常

 显示java.lang.NullPointerException在android.widget.ArrayAdapter.getCount
 

如何隐藏在ListView直到用户第一次搜索，然后取消隐藏它来显示结果。我将如何正确初始化适配器？

下面是我的适配器

 公共类SongsAdapter扩展ArrayAdapter＆LT;宋＆GT; {
    公共SongsAdapter（上下文的背景下，ArrayList的＆LT;宋＆GT;歌曲）{        超（背景下，0，歌）;
    }    @覆盖
    公共查看getView（INT位置，查看convertView，父母的ViewGroup）{
        宋歌=的getItem（位置）;        如果（convertView == NULL）
            convertView = LayoutInflater.from（的getContext（））膨胀（R.layout.item_song，父母，假的）。        TextView的ARTISTNAME =（TextView中）convertView.findViewById（R.id.artistName）;
        TextView的TRACKNAME =（TextView中）convertView.findViewById（R.id.trackName）;        artistName.setText（song.getArtist（））;
        trackName.setText（song.getTitle（））;        返回convertView;
    }
}
 

解决方案

您可以检查ArrayList是在getCount将方法无效，并返回相应的数据。

 公共类SongsAdapter延伸BaseAdapter {ArrayList的＆LT;宋＆GT; mList;
上下文mContext;公共SongsAdapter（上下文的背景下，ArrayList的＆LT;宋＆GT;歌曲）{    mList =歌曲;
    mContext =背景;}@覆盖
公众诠释的getCount（）{
    如果（mList == NULL）
    {        返回0;
    }
    其他{        返回mList.size（）;
    }
}@覆盖
公共对象的getItem（INT位置）{
    返回mList.get（位置）;
}@覆盖
众长getItemId（INT位置）{
    返回0;
}@覆盖
公共查看getView（INT位置，查看convertView，父母的ViewGroup）{
      宋歌=的getItem（位置）;    如果（convertView == NULL）
        convertView = LayoutInflater.from（的getContext（））膨胀（R.layout.item_song，父母，假的）。    TextView的ARTISTNAME =（TextView中）convertView.findViewById（R.id.artistName）;
    TextView的TRACKNAME =（TextView中）convertView.findViewById（R.id.trackName）;    artistName.setText（song.getArtist（））;
    trackName.setText（song.getTitle（））;    返回convertView;
}
}
 

标记此，如果它可以帮助别人让我知道如果你需要任何说明。快乐编码。

I have a a customer adapter (SongsAdapter) that extends ArrayAdapter and it contains an array of Song objects. In my fragments onCreateView method I'm trying to initialize this adapter.

adapter = new SongsAdapter(getContext(), arrayOfSongs);

the problem is that arrayOfSongs is initially null. The user should search for a song on the iTunes database and when I get a response, I parse the JSON and create song objects and then add them to my adapter

adapter.addAll(songs); 

and then

adapter.notifyDataSetChanged();

but I'm getting an exception

java.lang.NullPointerException at android.widget.ArrayAdapter.getCount

How can I hide the listview until the first search by the user, and then unhide it to display the results. How would I properly initialize the adapter?

Here is my adapter

public class SongsAdapter extends ArrayAdapter<Song> {


    public SongsAdapter(Context context, ArrayList<Song> songs) {

        super(context, 0, songs);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Song song = getItem(position);

        if (convertView == null)
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.item_song, parent, false);

        TextView artistName = (TextView) convertView.findViewById(R.id.artistName);
        TextView trackName = (TextView) convertView.findViewById(R.id.trackName);

        artistName.setText(song.getArtist());
        trackName.setText(song.getTitle());

        return convertView;
    }
}

解决方案

You can check if the arraylist is null in getCount method and return the data accordingly.

  public class SongsAdapter extends BaseAdapter {

ArrayList<Song> mList;
Context mContext;

public SongsAdapter(Context context, ArrayList<Song> songs) {

    mList = songs;
    mContext = context;

}



@Override
public int getCount() {
    if(mList==null)
    {

        return 0;
    }
    else {

        return mList.size();


    }
}

@Override
public Object getItem(int position) {
    return mList.get(position);
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
      Song song = getItem(position);

    if (convertView == null)
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.item_song, parent, false);

    TextView artistName = (TextView) convertView.findViewById(R.id.artistName);
    TextView trackName = (TextView) convertView.findViewById(R.id.trackName);

    artistName.setText(song.getArtist());
    trackName.setText(song.getTitle());

    return convertView;
}
}

Mark this up if it helps else let me know if you need any description. Happy coding.

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