Android - Controlar volumen de Mediaplayer desde MainActivity

package com.increasedecreasemediaplayervolume_android_examples.com;

import android.app.Activity;

import android.content.Context;

import android.media.AudioManager;

import android.os.Bundle;

import android.widget.SeekBar;

import android.widget.SeekBar.OnSeekBarChangeListener;

import android.widget.TextView;

public class MainActivity extends Activity {

 SeekBar seekbar;

 TextView textview;

 AudioManager audioManager;

 @Override

 protected void onCreate(Bundle savedInstanceState) {

 super.onCreate(savedInstanceState);

 setContentView(R.layout.activity_main);

 seekbar = (SeekBar)findViewById(R.id.seekBar1);

 textview = (TextView)findViewById(R.id.textView1);

 audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

 seekbar.setMax(audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC));

 seekbar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {

 @Override

 public void onProgressChanged(SeekBar seekBar, int i, boolean b) {

 textview.setText("Media Volume : " + i);

 audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, i, 0);

 }

 @Override

 public void onStartTrackingTouch(SeekBar seekBar) {

 }

 @Override

 public void onStopTrackingTouch(SeekBar seekBar) {

 }

 });

 }

}