cocos2dx 3.3 quick lua 实现返回键退出程序

<span style="font-size:18px;">    local layer = display.newLayer()        self:addChild(layer,-10)      layer:setKeypadEnabled(true)      layer:addNodeEventListener(cc.KEYPAD_EVENT, function (event)          if event.key == "back" then  --返回键            print("back")  --弹出一个对话框，点击yes退出程序            device.showAlert("Confirm Exit", "Are you sure exit game ?", {"YES", "NO"}, function (event)                if event.buttonIndex == 1 then                      cc.Director:getInstance():endToLua()                else                      device.cancelAlert()  --取消对话框                 end              end)                   elseif event.key == "menu" then  --菜单键            print("menu")                       end            end) </span>