使用硬件后退按钮在返回时结束 MediaPlayer

在我的应用程序中，在查看幻灯片时实现了声音播放。当我更改幻灯片或使用主页按钮退出活动时，媒体播放器将终止。但是，如果我使用手机/平板电脑的硬件“返回”按钮退出幻灯片视图，MediaPlayer 仍然在后台运行，这与应用程序的逻辑不对应。
告诉我如何将 MediaPlayer 的停止“固定”到按下硬件“返回”按钮？

public class SliderActivity extends AppCompatActivity implements CompoundButton.OnCheckedChangeListener {
    static final String TAG = "myLogs";
    ViewPager viewPager;
    CustomSwipeAdapter adapter;
    ToggleButton toggleButton;
    ImageButton imageButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setContentView(R.layout.activity_slider);
        imageButton = (ImageButton) findViewById(R.id.imageButtonHome);
        View.OnClickListener clickHome = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(mp !=null && mp.isPlaying()){
                    mp.stop();
                }
                GoHome();
            }
        };

        imageButton.setOnClickListener(clickHome);
/*
 * Читаем json и создаем из него объект книги bookFiles
 */
        Gson gson = new Gson();
        int bookId = GetBookId();
        String fileName = "book_" + bookId + ".json";
        String gsResult = MyJSON.getData(getApplicationContext(), fileName);
        BookFiles bookFiles = gson.fromJson(gsResult, BookFiles.class);

        final String folderB = "bookfiles_" + bookId;
        /*
        Получаем из объекта bookFiles массивы путей к файлам книги
         */
        ArrayList<String> pagesFiles = bookFiles.getPagesPath();
        final ArrayList<String> soundsFiles = bookFiles.getSoundsPath();

        viewPager = (ViewPager) findViewById(R.id.view_pager);
        viewPager.setPageTransformer(true, new ZoomOutPageTransformer());
        adapter = new CustomSwipeAdapter(this, pagesFiles);
        viewPager.setAdapter(adapter);
        toggleButton = (ToggleButton) findViewById(R.id.imageButtonPlay);

        //слушаем номер слайда при перелистывании
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            Boolean first = true;
            @Override
            public void onPageScrolled(final int position, float positionOffset, int positionOffsetPixels) {
                if (first && positionOffset == 0 && positionOffsetPixels == 0){
                    onPageSelected(0);
                    first = false;
                }
                mp.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    int pagen = position+1;
                    @Override
                    public void onCompletion(MediaPlayer mp) {
                        viewPager.setCurrentItem(pagen, true);
                    }
                });

            }

            @Override
            public void onPageSelected(int position) {
                String nameS = Uri.parse(soundsFiles.get(position)).getLastPathSegment();
                if(mp != null){
                    mp.stop();
                }
                getMedia(nameS, folderB);
                toggleButton.setOnCheckedChangeListener(SliderActivity.this);

                if (toggleButton.isChecked()){
                    mp.start();

                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

    }

    public int GetBookId() {
        Intent intent = getIntent();
        int bookId = intent.getIntExtra("bookId", 1);
        return bookId;
    }

    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if (isChecked) mp.start();
        else if (mp.isPlaying()) {
            mp.pause();
        }

    }

    public void getMedia(String nameS, String folderB) {
        try {
            final String soundPath = String.valueOf(getApplicationContext().getExternalFilesDir(folderB));
            final Uri souF = Uri.fromFile(new File(soundPath, nameS));
            final MediaPlayer mp = MyPlayer.getMp(getApplicationContext(), souF);
            mp.setAudioStreamType(AudioManager.STREAM_MUSIC);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void GoHome() {

        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Intent intent = new Intent(SliderActivity.this, MainActivity.class);
                startActivity(intent);
                finish();
            }
        }, 10);
    }

}