My android application cannot play again when clicking button - android-mediaplayer

Question

I'm new in android programming. My first application is an android mediaplayer.
I built two buttons : one to play a song, and another to stop it.
My application is running correctly ; the problem is that i can play and stop it, but I cant play the song again.
I tried to use setDataSource() but it triggers an error.
Here's the code ; the file is in raw/song.mp3
package com.example.test6;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
MediaPlayer mp;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mp = MediaPlayer.create(this,R.raw.song);
setContentView(R.layout.activity_main);
final Button btnPlay = (Button)this.findViewById(R.id.button1);
final Button btnStop = (Button)this.findViewById(R.id.button2);
btnPlay.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
mp.start();
}
});
btnStop.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
mp.stop();
mp.reset();
if(mp.isPlaying()){
mp.stop();
}else{
mp.setDataSource("res/raw/song.mp3");
mp.prepare();
mp.start();
}
});
}
}

Answer 1

First of all, you don't need to set the data source manually if you're doing the creation like this: MediaPlayer.create(this, R.raw.song); Also, in that case, you don't need to call prepare() because MediaPlayer.create() does that for you.
I would suggest this kind of approach (assuming you don't want the start button to do anything if it's already playing):
Start button listener:
if (mp==null) {
mp = MediaPlayer.create(this, R.raw.song);
}
if (!mp.isPlaying()) {
mp.start();
}
Stop button listener:
if (mp!=null) {
if (mp.isPlaying()) {
mp.stop();
}
mp.release();
mp = null;
}
I didn't test this, so I'm looking forward to your response