WWDC Notes

Cocoa Touch Best Practices

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Small improvements can make a big impact on your iOS app's performance and launch time. Learn best practices to optimize your UIKit-based applications. See how to future-proof your app for what may be next, and walk through numerous real world examples for more responsive and dynamic collection and table views.

App Lifecycle

Beyond App Launch, Being responsive to every input

  • Put on the work to the background queue, when you are done with it, put it back to main queue.

Leverage Frameworks

  • Target two most recent major releases

Views and View Controllers

Layout to Proportions

  • Avoid hard-coded layout values

Size Classes

  • Some size thresholds trigger major change
  • Properties, not Tags. Keep a property instead.

Leverage UIViewControllerTransitionCoordinator

  • 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

Constraint Specificity

  • De-duplicating constraints
    • Duplicates are implied by existing constraints
    • Duplicates cause excess work in layout engine
  • Create flexible constraints
    • Avoid hard-coded values
    • Describe constraints using bounds
  • Fully specify constraints
  • Testing and debugging
    • -[UIView hasAmbiguousLayout], when called on UIWindow, returns result for entire view tree
    • -[UIView _autolayoutTrace], Call this method on a view. It returns a string with diagnostic information about the entire view hierarchy containing that view. Ambiguous views are labeled, and so are views that have translatesAutoresizingMaskIntoConstraints set to YES.
    • This could be used in Unit Test, try call -[UIView hasAmbiguousLayout] first, if it returns YES, then call -[UIView _autolayoutTrace] to help figure out the cause.

Table and Collection Views

Self-Sizing Cells

  • Fully specify constraints
  • Width = input; height = output.
  • Tip: add a constraint to cell's content view, height

Animating Height Changes

Naive way: update the model, then call tableView.reloadData()

Promoted way:

  • tableView.beginUpdates
  • Update model
  • Update cell contents, might just call tableView.cellForRowAtIndexPath and update the content with corresponding model.
  • tableView.endUpdates ### Fast CollectionView Layout Invalidation
  • Invalidate on bounds change
  • Build targeted invalidation context
  • Repeat as necessary

This note was originally published at https://github.com/antonio081014/WWDC_Learning_Review

Missing anything? Corrections? Contributions are welcome 😃

Written by

antonio081014

Yi Ding

Write the Code, Change the World.