Listview 设置默认选中项

Cocos2d-x
#1 
function ServantWindow:onEnter()
    self._list:addEventListener(function(sender, eventType)
        if eventType == ccui.ListViewEventType.ONSELECTEDITEM_END then

            local index = sender:getCurSelectedIndex()

        end
    end)
    for i = 1, 4 do
        local img = "servantinfo/yongbingtouxiang0"..i..".png"
        local custom_button = ccui.Button:create(img, img)
        self._list:addChild(custom_button) 
    end
end


```
各位大神，请问怎么设置listview的默认选中项，也就是第一次加载的时候自动选中一项，或者在加载的时候进行一次模拟点击？？？？:6::6::6::6::6: