@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
       if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
              // 杀死本进程
              android.os.Process.killProcess(android.os.Process.myPid());
              return true;
       }
  return super.onKeyDown(keyCode, event);
}