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

• 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