IOS View outer layer of strange black line

Recently, a problem was encountered in order to build a Label that automatically adapts to the content. Based on the content, I calculate the required size and then set the new size to the Label.

But when displayed, a strange phenomenon appears, and the top of the Label always has a shallow black line. It's not obvious, it's a bit like adding a border.

The reason I was very hard to find, the reason is actually very simple:

-The calculated size is a floating-point number with several decimal places, and UIView seems to be uncomfortable with the size of such a precision. I converted the floating-point number directly to int, solving the problem.

IOS View outer layer of strange black line