Creating an adapter for listview without passing an array initially

问题

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;
    }
}

回答1:

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.

来源：https://stackoverflow.com/questions/36157482/creating-an-adapter-for-listview-without-passing-an-array-initially

标签

android

listview

android-adapter