Cria uma lista que exibe os mp3 disponíveis no Storage.

Mp3Fragment.java

package tl.domacoski;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import android.annotation.SuppressLint;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

/**
 * {@link Fragment} que exibe a lista de mp3 disponiveis no Storage.
 *
 */
public class Mp3Fragment extends Fragment {


	private MediaPlayer mPlayer;
	private ListView listView;

	@Override
	public View onCreateView(LayoutInflater inflater, ViewGroup container,
			Bundle savedInstanceState) {
		final View rootView = inflater.inflate(R.layout.mp3_fragment, container, false);

		this.listView = ListView.class.cast(rootView.findViewById(R.id.lista));

		final List<TabSom3> list = getPlayList();
		final Adapter adapter = new Adapter(this, list);
		this.listView.setAdapter(adapter);
		this.listView.refreshDrawableState();
		return rootView;
	}




	/**
	 * Retona a lista de objetos comforme arquivos existentes.
	 * @return {@link List}
	 */
	public  List<TabSom3> getPlayList(){
		final List<TabSom3> list = new ArrayList<TabSom3>(0);
		final List<File> files = getMp3File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC));

		for(final File mp3 :files){
			final TabSom3 som3 = new TabSom3();
			som3.ArqSom = mp3.getAbsolutePath();
			som3.NomeSom = mp3.getName();
			list.add(som3);
		}
		return list;
	}


	/**
	 * Retorna todos os arquivos que contem mp3 no nome.
	 * @param file
	 * @return {@link List}
	 */
	public List<File> getMp3File(final File file){
		final List<File> lst = new ArrayList<File>(0);
		for(final File child : file.listFiles()){
			if(child.isDirectory()){
				final List<File> lst2 = getMp3File(child);
				if(null != lst2){
					lst.addAll(lst2);
				}
			}else{
				if(isMp3(child)){
					lst.add(child);
				}
			}
		}


		return lst;
	}
	/**
	 * Retorna true se contem mmp3 no nome do arquivo
	 * @param file
	 * @return boolean
	 */
	private boolean isMp3(final File file){
		if(null == file) return false;
		return file.getName().contains("mp3");
	}


	/**
	 * Toca um arquivo atraves do {@link MediaPlayer} 
	 * @param tabSom3
	 */
	public void play(final TabSom3 tabSom3){
		if(null == tabSom3) return;
		if(null != mPlayer){
			mPlayer.stop();
		}
		try {
			mPlayer = new  MediaPlayer();
			mPlayer.setDataSource(getActivity(), Uri.parse(tabSom3.ArqSom));
			mPlayer.prepare();   
			mPlayer.start();
		} catch (Exception e) {
			e.printStackTrace();
		}


	}

	/**
	 * Classe controlada pelo {@link Adapter}
	 */
	static class TabSom3{
		public String NomeSom;
		public String ArqSom;
	}
	/**
	 *Controla a {@link ListView}.
	 *Gerencia o click sobre um elemento da lista.
	 */
	@SuppressLint("ResourceAsColor")
	static class Adapter extends ArrayAdapter<TabSom3> implements View.OnClickListener{

		private final LayoutInflater inflater;
		final Mp3Fragment fragment;

		public Adapter(Mp3Fragment context, final List<TabSom3> list) {
			super(context.getActivity(), R.layout.audio_item, list);
			this.inflater = LayoutInflater.from(context.getActivity());
			this.fragment = context;
		}


		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			TabSom3 tab = null;
			if(convertView == null){
				convertView = inflater.inflate(R.layout.audio_item, null);
				tab = getItem(position);
				convertView.setTag(tab);
				convertView.setOnClickListener(this);
			}else{
				if(null != convertView.getTag()){
					tab = TabSom3.class.cast(convertView.getTag());
				}
			}

			if(null != tab){
				TextView.class.cast(convertView.findViewById(R.id.nameSom)).setText(tab.NomeSom);
			}
			return convertView;
		}



		@Override
		public void onClick(final View v) {
			if(null == v || null == v.getTag()) return;
			fragment.play(TabSom3.class.cast(v.getTag()));
			v.setBackgroundColor(android.R.color.darker_gray);

		}

	}

}