As you probably notices, simple screen drawing is useless if it comes to OpenGL view. So is it possible to generate UIImage from such? Of course, lets suppose your custom drawing class extends UIView, then just add:

This code works in XCode 9 and Swift 3.x.

Sooner or later, you will face the problem with object which are not deallocating. How to check if object gets deallocated? Just use deinit method like below:

If you won’t see such message when you think you class should be gone, the easiest way is to debug allocations. Because the most common reason for such behavior are strong references, you can print allocation counter this way:

But where to put this? First of all, in all you initialization methods. Just add some those prints after each few lines, and you should see where counter is growing. The same in cleanup methods, or if you dont have any, you can put this somewhere when your view controller is closing, like:

And how to avoid strong references? The most common mistake, is using self in blocks, this is the place where you should use [unowned self], this way:

If you were using NSCoder in Swift 2, I’m pretty sure you used such code:

decoder.decodeObject(forKey: "name") as! String
decoder.decodeObject(forKey: "number") as! Int

Now, in Swift 3, using such construction, will cause:

fatal error: unexpectedly found nil while unwrapping an Optional value

So is there any solution for this? Yes, you need to use explicit methods to integers, floats, bools and some other types. Just rewrite this code as:
decoder.decodeObject(forKey: "name") as! String
decoder.decodeInteger(forKey: "number")

And this error will be gone. Available methods below:
decodeBool
decodeInteger
decodeCInt (returns Int32)
decodeInt32
decodeInt64
decodeFloat
decodeDouble
decodeBytes