Android: Store ListView data in an ArrayList of Hashmap<String, String>

Question

I am making a small MP3 Player for android. For my project I wrote a class (MP3Finder) that returns the located songs in an ArrayList of HashMap.

Until now, my app just displays the songs located on the sdcard in a listview from which an user can start playing a song.

Now I would like that a user should be able to add different songs to a playlist. For this reason I made a songlist activity with a listview that contains all the songs as checkedTextView items. The problem is that I don't know, how to store the checked (selected by the user) songs from the songlist back into an ArrayList of HashMap, which is to be send to the playlist activity. I hope you understand what I want to do.

Here is the source code of my SongListActivity:

public class SongListActivity extends AppCompatActivity {

// List of mp3 files
ArrayList<HashMap<String, String>> MP3List = new ArrayList<>();

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

    Button isChecked = (Button) findViewById(R.id.btn_is_checked);
    final ListView listView = (ListView) findViewById(R.id.list_view);

    MP3Finder mp3Finder = new MP3Finder();

    // Get all mp3's from sdcard
    this.MP3List = mp3Finder.getMP3List();

    // Add items to ListView
    ListAdapter adapter = new SimpleAdapter(this, MP3List, R.layout.activity_item, new String[] { "mp3Title" }, new int[] {
          R.id.mp3_title});

    listView.setAdapter(adapter);
    listView.setOnItemClickListener(new CheckBoxClick());
    listView.setChoiceMode(AbsListView.CHOICE_MODE_MULTIPLE);

    isChecked.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            SparseBooleanArray checked = listView.getCheckedItemPositions();

            int len = listView.getCount();

            for (int i = 0; i < len; i++) {
                if (checked.get(i)) {
                    // ...here is the part, where I want to store the selected songs back
                    // in an ArrayList of HashMap...
                }
            }
        }
    });
}

public class CheckBoxClick implements AdapterView.OnItemClickListener {

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        CheckedTextView checkedTextView = (CheckedTextView) view;

        if (checkedTextView.isChecked()) {
            Toast.makeText(MainActivity.this, "checked", Toast.LENGTH_SHORT).show();

        } else {
            Toast.makeText(MainActivity.this, "unchecked", Toast.LENGTH_SHORT).show();
        }
    }
}

Any help or suggestions would be appreciated.

Answer 1

First of all you need to declare your ArrayList as static so that it could persist across activities.

 static ArrayList<HashMap<String, String>> MP3List = new ArrayList<>();

Now on button click, you need to create a new HashMap and put it inside MP3List

isChecked.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            HashMap<String,String> hashmap = new HashMap();

            SparseBooleanArray checked = listView.getCheckedItemPositions();

            int len = listView.getCount();

            for (int i = 0; i < len; i++) {
                if (checked.get(i)) {
                   String path = //Get your path here;
                   String title = // Get your title here;
                   hashmap.put(path,title);
                }
            }
          MP3list.add(hashmap);
        }
    });

So as soon as you click a button in SongListActivity, it will go through all the items in a for loop and put checked items in the HashMap. When the loop is over, you can add the HashMap inside the ArrayList.