如图：
屏幕快照 2018-09-26 下午2.29.47.png
代码：
private typealias DidSelectedItemBlock = (_ atIndexPath:IndexPath, _ modelGroup:BGGroup,_ modelBGImage:BGImage) -> ()
var didSelectedItemBlock:DidSelectedItemBlock!
报错：
error：Property must be declared private because its type uses a private type
说明类型是私有的声明的该类型的变量也必须是私有的。
