Android：如何将数据从适配器传递到OnClickListener的Main Activity

Question

I am really stuck here, I am new to Programming. I achieved a lot in my Music App, but now I made a button in my listViewAdapter with a OnClickListener and I want to add a Song to the favList ArrayList in my MainActivity. With this code I have the Song I want, but how do I get it into the List?

Here is my code for this:

class SongAdapter extends ArrayAdapter<Song> {

    SongAdapter(Context context, ArrayList<Song> songs) {
        super(context, 0, songs);
    }

    @NonNull
    @Override
    public View getView(final int position, View convertView, @NonNull ViewGroup parent) {
        // Check if the existing view is being reused, otherwise inflate the view
        View listItemView = convertView;
        if (listItemView == null) {
            listItemView = LayoutInflater.from(getContext()).inflate(R.layout.list_item, parent, false);
        }
        Song currentSong = getItem(position);

        TextView songNameTextView = (TextView) listItemView.findViewById(R.id.song_name);
        assert currentSong != null;
        songNameTextView.setText(currentSong.getSongName());
        TextView songArtistTextView = (TextView) listItemView.findViewById(R.id.song_artist);
        songArtistTextView.setText(currentSong.getArtist());

        ImageButton addToPlaylistButton = (ImageButton) listItemView.findViewById(R.id.addToPlaylist);
        addToPlaylistButton.setTag(position);
        addToPlaylistButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int position = (Integer) view.getTag();
                Song song = getItem(position);
                Toast.makeText(view.getContext(), song.getAlbum().toString(), Toast.LENGTH_LONG).show();
            }
        });

        return listItemView;
    } }

And here are the parts from my MainActivity:

final ArrayList<Song> songs = new ArrayList<>();  final ArrayList<Song> favSongs = new ArrayList<>();

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.song_list);
         //Setup the Listview for the Songs
            SongAdapter adapter = new SongAdapter(this, songs);
            ListView listView = (ListView) findViewById(R.id.list);
            listView.setItemsCanFocus(true);
            listView.setAdapter(adapter); 
            }

Answer 1

You should create own OnItemClickListener in activity, set it to adapter and then dispatch onClick event with position to that custom listener.

interface OnItemClickListener {
    void onItemClicked(int position);
}

in activity:

private OnItemClickListener listener = new OnItemClickListener() {
    public void onItemClicked(int position) {
        Song song = adapter.get(position);
        //do whatever you want with song
    }
}

//creation of adapter
SongAdapter adapter = new SongAdapter(this, songs, listener);

in adapter:

private OnItemClickListener onClickListener;

SongAdapter(Context context, ArrayList<Song> songs, OnItemClickListener onClickListener) {
    super(context, 0, songs);
    this.onClickListener = onClickListener;
}

//in getView
addToPlaylistButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (onClickListener != null) {
                onClickListener.onItemClicked(position);
            }
        }
    });

Answer 2

You can just use the reference to the songs that you pass to the adapter when you create it. Something like this:

class SongAdapter extends ArrayAdapter<Song> {

    private ArrayList<song> songs;

    SongAdapter(Context context, ArrayList<Song> songs) {
        this.songs = songs
        super(context, 0, songs);
    }

    (snip...)

        @Override
        public void onClick(View view) {
            int position = (Integer) view.getTag();
            Song song = getItem(position);

            songs.add(song);
            (...)
        }
    }); // end of listener

}
}

And your ArrayList will now contain your Song .

Another, simpler way to do this would be to make the ArrayList in the main Activity static , so you can refer to it from anywhere, however, this is not recommended on Android.