/*****************************************************/
//add by xxnan
Runnable mBackLongPress = new Runnable() {
  public void run() {
   mBackPressed = false;
    performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false);
    sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
    showGlobalActionsDialog();
  }
 };
/*****************************************************/

performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false);
sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);

/*****************************************************/
  //add by xxnan
  if ((keyCode == KeyEvent.KEYCODE_BACK) && !down) {
   mHandler.removeCallbacks(mBackLongPress);//应该是取消长按
  }
  if (mBackPressed) {
  if (keyCode == KeyEvent.KEYCODE_BACK)
   {
    if (!down) {
     mBackPressed = false;
    }
   }
  }
  if ((keyCode == KeyEvent.KEYCODE_BACK))
  {
     if (down && repeatCount != 0) {//如果按下back键而且repeatCount不等于0，(只按一下back键repeatCount的值为0，长按repeatCount的值就会随时间的增加而增加，而且当长按back键repeatCount>10才会弹出关机框)
      if (!keyguardOn) {//不管长按还是短按keyguardOn都等于false
      Log.i("longpressback","longpressback");
      mHandler.postDelayed(mBackLongPress, ViewConfiguration.getGlobalActionKeyTimeout());//调用长按back的线程mBackLongPress
      }
      mBackPressed = true;
    }
  }
  /*****************************************************/