Cocoa-Touch-Best-Practices.md

Cocoa Touch Best Practices

📅 2020.1.30 (THU)

WWDC 2015 | Session : 231| Category : UIKit

🔗 Cocoa Touch Best Practices - WWDC 2015 - Videos - Apple Developer

App Lifecycle

First best practice is launch quickly. That's how you appear responsive when the user taps on your icon and right away they get your app ready to interact with.

Launch Quickly

• Return quickly from applicationDidFinishLaunching
  • Defer long running work
  • App killed if too much time passes

Beyond App Launch

Being responsive to every input

• Not just about asynchrony
• Move long running work to background queues

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]?) -> Bool {
    	globalDataStructure = MyCoolDataStructure()
    
    	// defer work until later
    	DispatchQueue.global().async {
    		globalDataStructure.fetchDataFromDatabase()
    	}
    
    	return true
    }

Whenever it does run, user interface continues to happen, and your application seems responsive all the time. So this technique, putting the work on background queues, can be applied anytime in your app.

Launch Quickly Again

That app is the first on that's going to die when the foreground app needs additional memory.

⬇️

Leverage Frameworks

Properly manage version change

• Target two most recent major release
• Include version fallbacks
• Have an else clause

Views and View Controllers

Layout on Modern Devices

No longer makes sense to build layouts that are built specific for a particular dimension that your ViewController expects to be in.

Instead, layout in general wants to think of itself as being done to proportions, and we do that by specifically avoiding hard-coded values in the layout of Views and ViewControllers.

Layout to Proportions

• Avoid hard-coded layout values
• Either or both dimensions may scale

Size Classes

• Some size thresholds trigger major change
• Packaged in UITraitCollection

Properties, No Tags!

Avoid setTag: and viewWithTag:

• Possible collisions with other code
• No compiler warnings
• No runtime errors

Instance variables and properties provide better alternative

    class ViewController: UIViewController {
    	var imageView: UIImageView
    
    	overrride func viewDidLoad() {
    		super.viewDidLoad()
    
    		imageView = UIView(frame: CGRect(x: 0, y :0, widht: 50, height: 50))
    		view.addSubview(imageView)
    	}
    }

Keep real reference to that view, also has better type information because viewWithTag: only is a type UIView.

Make Timing Deterministic

Leverage UIViewControllerTransitionCoordinator

(to know what the timings are for the animations that you have)

• Animate alongside a transition
• Get accurate completion timing
• Support interactive and cancelable animations

Auto Layout

Modify Constraints Efficiently

• Identify constraints that get changed, added, or removed
• Unchanged constraints are optimized
• Avoid removing all constraints
• Use explicit constraint references

❌❌❌

    override func updateViewConstraints() {
    	super.updateViewConstraints()
    
    	view.removeConstraints(view.constraints())
    	view.addConstraints(self.genereatdConstraints())
    }

✅✅✅

    override func updateViewConstraints() {
    	super.updateViewConstraints()
    
    	view.removeConstraints(imageViewHorizontalConstraint)
    	imageViewHorizontalConstraints = self.generatedImageViewHorizontalConstraint()
    	view.addConstraint(imageViewHorizontalConstraint)
    }

Constraint Specificity

De-duplicating constraints

• Duplicates are implied by existing constraints
• Duplicates causes excess work in layout engine It's solving for these constraints because they are there, but didn't actually need to solve for them.

This view hierarchy would have laid out exactly the same if I hadn't specified the left margin of the bottom view.

Get rid of that we'll be faster.

Create flexible constraints

• Avoid hard-coded values
• Describe constraints using bounds

Fully specify constraints

• Underspecification generates ambiguity
• Ambiguity is undefined View might come out different ways different times I run my app.

Testing and debugging

-[UIView hasAmbiguousLayout] It will let you know if there's ambiguity in you view.

• When called on UIWindow, returns result for entire view tree

-[UIView _autolayoutTrace]

• Both can be used for unit testing

Table and Collection View

Self-Sizing Cells

• Fully specify constraints
• Width = input, height = output

Animation Height Changes

• tableView.beginUpdates
• Update model
• Update cell contents
• tableView.endUpdates

Fast Collection View Layout Invalidation

Modify only what is needed

1. Invalidate on bounds change
2. Build targeted invalidation context
3. Repeat as necessary