请教一个ccui.Button loadTextureNormal的问题

Cocos2d-x Lua
#1

请教大虾

local IMG_BUTTON_UPGRADEOPT    = "images/button/UpgradeOpt.png";
local btnUpgrade = ccui.Button:create(IMG_BUTTON_UPGRADEOPT)
btnUpgrade.loadTextureNormal(IMG_BUTTON_UPGRADEOPT)


```


结果提示
 error in function 'lua_cocos2dx_ui_Button_loadTextureNormal'. argument #1 is 'string'; 'ccui.Button' expected.
#2

第3行 用冒号