let maskPath = UIBezierPath(roundedRect: bounds,
byRoundingCorners: [.topLeft, .topRight], cornerRadii:CGSize(width:10, height:10))
let masklayer = CAShapeLayer()
masklayer.frame = bounds
masklayer.path = maskPath.cgPath
cell?.layer.mask = masklayer
*bounds是重點,賦值錯誤會有UI上的bug