添加UICollectionView作为UICollectionReusableView的子视图reloadData不起作用，我想念的是什么？

I'm try to add UICollectionView to my custom UICollectionReusableView in runtime, in main form I have a UICollectionView(named mainView) to show first-level menus to user, when user did select cell in mainView it will expand second-level menus in foot section(and call FolderContentView::loadSubMenus method), following is my wont work code, please help.I'm try to add UICollectionView to my custom UI