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WWDC2015_Session231_Cocoa_Touch_Best_Practices.md

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WWDC2015 Session 231 Cocoa Touch Best Practices

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
  • Propertyeis, 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