dummy

bug I meeted: use self.addShadow(.black, sRadius: 2, sOpacity: 0.2, offset: (-1, -1)) not works, addShadow is below

however, I added it after snp constrains wrote, but when I break at this line, I found that it's frame is equal to .zero. After about a hr struggling with articles, I knowed that it's frame changes after layoutSubviews is called

so I wrote like this

which works perfectly.