play the pressed song

app/src/main/AndroidManifest.xml

@@ -3,6 +3,9 @@
     package="musicplayer.simplemobiletools.com"
     xmlns:android="http://schemas.android.com/apk/res/android">
 
+    <uses-permission android:name="android.permission.WAKE_LOCK"/>
+    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
+
     <application
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
@@ -18,5 +21,8 @@
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
         </activity>
+
+        <service android:name="musicplayer.simplemobiletools.com.MusicService"/>
+
     </application>
 </manifest>

app/src/main/java/musicplayer/simplemobiletools/com/MainActivity.java

@@ -1,9 +1,14 @@
 package musicplayer.simplemobiletools.com;
 
+import android.content.ComponentName;
 import android.content.ContentResolver;
+import android.content.Context;
+import android.content.Intent;
+import android.content.ServiceConnection;
 import android.database.Cursor;
 import android.net.Uri;
 import android.os.Bundle;
+import android.os.IBinder;
 import android.provider.MediaStore;
 import android.support.v7.app.AppCompatActivity;
 import android.view.View;
@@ -21,8 +26,11 @@ import butterknife.ButterKnife;
 import butterknife.OnClick;
 
 public class MainActivity extends AppCompatActivity {
-    private static final int MIN_DURATION_SECS = 20;
+    private static final int MIN_DURATION_MS = 20000;
     private ArrayList<Song> songs;
+    private MusicService musicService;
+    private boolean isMusicBound;
+
     @Bind(R.id.playPauseBtn) ImageView playPauseBtn;
     @Bind(R.id.songs) ListView songsList;
     @Bind(R.id.songTitle) TextView titleTV;
@@ -45,9 +53,14 @@ public class MainActivity extends AppCompatActivity {
                 songPicked(position);
             }
         });
+
+        final Intent intent = new Intent(this, MusicService.class);
+        bindService(intent, musicConnection, Context.BIND_AUTO_CREATE);
+        startService(intent);
     }
 
     private void songPicked(int pos) {
+        musicService.setSong(pos, true);
         updateSongInfo(songs.get(pos));
     }
 
@@ -76,7 +89,7 @@ public class MainActivity extends AppCompatActivity {
             final int artistIndex = musicCursor.getColumnIndex(MediaStore.Audio.Media.ARTIST);
             final int durationIndex = musicCursor.getColumnIndex(MediaStore.Audio.Media.DURATION);
             do {
-                if (musicCursor.getInt(durationIndex) > MIN_DURATION_SECS) {
+                if (musicCursor.getInt(durationIndex) > MIN_DURATION_MS) {
                     final long id = musicCursor.getLong(idIndex);
                     final String title = musicCursor.getString(titleIndex);
                     final String artist = musicCursor.getString(artistIndex);
@@ -87,6 +100,31 @@ public class MainActivity extends AppCompatActivity {
         }
     }
 
+    private ServiceConnection musicConnection = new ServiceConnection() {
+        @Override
+        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
+            MusicService.MyBinder binder = (MusicService.MyBinder) iBinder;
+            musicService = binder.getService();
+            musicService.setSongs(songs);
+            isMusicBound = true;
+        }
+
+        @Override
+        public void onServiceDisconnected(ComponentName componentName) {
+            isMusicBound = false;
+        }
+    };
+
+    @Override
+    protected void onDestroy() {
+        if (isMusicBound) {
+            isMusicBound = false;
+            unbindService(musicConnection);
+        }
+
+        super.onDestroy();
+    }
+
     @OnClick(R.id.previousBtn)
     public void previousClicked() {
         if (isPlaylistEmpty())

app/src/main/java/musicplayer/simplemobiletools/com/MusicService.java

@@ -1,13 +1,89 @@
 package musicplayer.simplemobiletools.com;
 
 import android.app.Service;
+import android.content.ContentUris;
 import android.content.Intent;
+import android.media.AudioManager;
+import android.media.MediaPlayer;
+import android.net.Uri;
 import android.os.Binder;
 import android.os.IBinder;
+import android.os.PowerManager;
+import android.provider.MediaStore;
 import android.support.annotation.Nullable;
+import android.util.Log;
 
-public class MusicService extends Service {
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Random;
+
+public class MusicService extends Service
+        implements MediaPlayer.OnPreparedListener, MediaPlayer.OnErrorListener, MediaPlayer.OnCompletionListener {
+    private static final String TAG = MusicService.class.getSimpleName();
+    private ArrayList<Song> songs;
     private final IBinder musicBind = new MyBinder();
+    private MediaPlayer player;
+    private ArrayList<Integer> playedSongIDs;
+    private Song currSong;
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        songs = new ArrayList<>();
+        playedSongIDs = new ArrayList<>();
+
+        initMediaPlayer();
+    }
+
+    public void initMediaPlayer() {
+        player = new MediaPlayer();
+        player.setWakeMode(getApplicationContext(), PowerManager.PARTIAL_WAKE_LOCK);
+        player.setAudioStreamType(AudioManager.STREAM_MUSIC);
+        player.setOnPreparedListener(this);
+        player.setOnCompletionListener(this);
+        player.setOnErrorListener(this);
+    }
+
+    public void playNext() {
+        setSong(getNewSongId(), true);
+    }
+
+    private int getNewSongId() {
+        final int cnt = songs.size();
+        if (cnt == 0) {
+            return -1;
+        } else if (cnt == 1) {
+            return 0;
+        } else {
+            final Random random = new Random();
+            int newSongIndex = playedSongIDs.size() - 1;
+            // make sure we do not repeat the same song
+            while (newSongIndex == playedSongIDs.size() - 1) {
+                newSongIndex = random.nextInt(cnt - 1);
+            }
+            return newSongIndex;
+        }
+    }
+
+    public void setSong(int songId, boolean addNewSong) {
+        if (player == null)
+            initMediaPlayer();
+
+        player.reset();
+        if (addNewSong)
+            playedSongIDs.add(songId);
+
+        currSong = songs.get(songId);
+
+        try {
+            final Uri trackUri = ContentUris.withAppendedId(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, currSong.getId());
+            player.setDataSource(getApplicationContext(), trackUri);
+        } catch (IOException e) {
+            Log.e(TAG, "setSong IOException " + e.getMessage());
+        }
+
+        player.prepareAsync();
+    }
 
     @Nullable
     @Override
@@ -15,6 +91,49 @@ public class MusicService extends Service {
         return musicBind;
     }
 
+    @Override
+    public boolean onUnbind(Intent intent) {
+        if (player != null && !player.isPlaying()) {
+            destroyPlayer();
+        }
+        return false;
+    }
+
+    public void setSongs(ArrayList<Song> songs) {
+        this.songs = songs;
+    }
+
+    @Override
+    public void onCompletion(MediaPlayer mp) {
+        if (player.getCurrentPosition() > 0) {
+            player.reset();
+            playNext();
+        }
+    }
+
+    @Override
+    public boolean onError(MediaPlayer mp, int what, int extra) {
+        player.reset();
+        return false;
+    }
+
+    @Override
+    public void onPrepared(MediaPlayer mp) {
+        mp.start();
+    }
+
+    @Override
+    public void onDestroy() {
+        super.onDestroy();
+        destroyPlayer();
+    }
+
+    private void destroyPlayer() {
+        player.stop();
+        player.release();
+        player = null;
+    }
+
     public class MyBinder extends Binder {
         MusicService getService() {
             return MusicService.this;