What you learned

Project 29 was a serious game with a lot going on, not least the dynamically rendered buildings with destructible terrain, the scene transitions and the UIKit/SpriteKit integration.

And in project 30 we took our first steps outside of Xcode and into Instruments. I could write a whole book on Instruments, partly because it’s extremely powerful, but also because it’s extremely complicated. As per usual, I tried to cherrypick things so you can see useful, practical benefits from what I was teaching, and certainly you have the skills now to be able to diagnose and result a variety of performance problems on iOS.

Here are some of the things you learned in this milestone:

• How to access the keychain using SwiftKeychainWrapper.
• How to force the keyboard to disappear by calling resignFirstResponder() on a text view. (And remember: it also works on text fields.)
• How to detect when your app is moving to the background by registering for the UIApplication.willResignActiveNotification notification.
• How to use LAContext from the LocalAuthentication framework to require Touch ID authentication.
• Using the stride() function to loop across a range of numbers using a specific increment, e.g. from 0 to 100 in tens.
• Creating colors using the hue, saturation, and brightness. As I said, keeping the saturation and brightness constant while choosing different hues helps you create similar color palettes easily.
• SpriteKit texture atlases. These are automatically made by Xcode if you place images into a folder with the .atlas extension, and are drawn significantly quicker than regular graphics.
• Using usesPreciseCollisionDetection to make collisions work better with small, fast-moving physics bodies.
• Transitioning between scenes with the presentScene() method and passing in a transition effect. We’ll be using this again in project 36, so you’ll have ample time to practice transitions.
• Using the blend mode .clear to erase parts of an image. Once that was done, we just recalculated the pixel-perfect physics to get destructible terrain.
• Adding dynamic shadows to views using layer.shadowRadius and other properties – and particularly how to use the layer.shadowPath property to save shadow calculation.
• The importance of using dequeueReusableCell(withIdentifier:) so that iOS can re-use cells rather than continually creating new ones.
• How the UIImage(named:) initializer has an automatic cache to help load common images. When you don’t need that, use the UIImage(contentsOfFile:) initializer instead.

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