android中关闭返回键

public boolean onKeyDown(int keyCode,KeyEvent event){
switch(keyCode){
case KeyEvent.KEYCODE_HOME:return true;
case KeyEvent.KEYCODE_BACK:return true;
case KeyEvent.KEYCODE_CALL:return true;
case KeyEvent.KEYCODE_SYM: return true;
case KeyEvent.KEYCODE_VOLUME_DOWN: return true;
case KeyEvent.KEYCODE_VOLUME_UP: return true;
case KeyEvent.KEYCODE_STAR: return true;
}
return super.onKeyDown(keyCode, event);
}