Android MusicPlayer 4

MainActivity.java

        // Media Playerの初期化
        mp = MediaPlayer.create(this, R.raw.music);
        mp.setLooping(true);
        mp.seekTo(0);
        mp.setVolume(0.5f, 0.5f);

        // 音量調節
        volumeBar = findViewById(R.id.volumeBar);
        volumeBar.setOnSeekBarChangeListener(
                new SeekBar.OnSeekBarChangeListener() {
                    @Override
                    public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
                      
                    }

                    @Override
                    public void onStartTrackingTouch(SeekBar seekBar) {

                    }

                    @Override
                    public void onStopTrackingTouch(SeekBar seekBar) {

                    }
                }
        );
    }

    public void playBtnClick(View view) {