I tried the tutorial from raywenderlich.com but the behavior was incorrect. The canvas or
UIImageView seems to move after lifting my finger.
It tried to run the official project from raywenderlich.com but it has the same strange behavior.
Luckily I found a solution, you need to change this line inside
// from UIGraphicsBeginImageContext(mainImageView.frame.size) // change to UIGraphicsBeginImageContext(view.frame.size)
And that’s it.