Android如何监听Home键和Back键？

protected static ArrayList sVisibleActivities = new ArrayList();

private static Boolean isExit = false;
private static Boolean hasTask = false;
Timer tExit = new Timer();
TimerTask task = new TimerTask() {

@Override
public void run() {
isExit = false;
hasTask = true;
}
};
protected void onPause() {  
if (!sVisibleActivities.contains(MusicActivity.this))
{
sVisibleActivities.add(MusicActivity.this);
}
super.onPause();
};
protected void onStop(){
if (sVisibleActivities.contains(MusicActivity.this))
{   
sVisibleActivities.remove(MusicActivity.this);
Intent intent = new Intent(MusicActivity.this, LocalMusicService.class);
intent.putExtra("cards", cards);
intent.putExtra("index", index);
intent.putExtra("count", count);
intent.putExtra("id", id);
intent.putExtra("play", "stop");
startService(intent);
btnPlay.setBackgroundResource(R.drawable.select_a_3_1_press);
seekBar.setProgress(0);
finish();

}
super.onStop();
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK
&& event.getAction() == KeyEvent.ACTION_DOWN) {
} 
Intent intent = new Intent(MusicActivity.this, LocalMusicService.class);
stopService(intent);
finish();
Toast.makeText(MusicActivity.this, "音乐已停止！",
Toast.LENGTH_LONG).show();
return false;
}