In the drawing update process "For some reason it is not reflected" I have encountered the scene several times.
At such times, the "life cycle" is generally involved. Classes such as UIViewController and UIView have something called ** processing flow **.
Super.viewDidLoad (), which you always see when creating a file, is just one part of it.
Below, the life cycle of UIViewController https://qiita.com/motokiee/items/0ca628b4cc74c8c5599d
Let's compare the life cycle to architecture. When building a house, first make a foundation and then build a skeleton. Then bring in walls, roofs, and then furniture. At this time, it is not possible to build a framework without creating a foundation. You will also need a wall to paint the wall.
A story similar to this is the life cycle. If you do not process at the right time, it will not be reflected.
That is the phenomenon that "drawing is not reflected". If you fall into such a case, first check the inheriting class and life cycle, Let's insert the drawing update process at an appropriate timing.