Adding Delight to Your iOS App

WWDC 2018

External Display Support

• Add a custom UI for external displays
• Consider the different display contexts
• Handle connection changes gracefully

Designing for Multiple Displays

How to support External Display

Handling Connectivity

• Is there an external display connected ?

• What happens when the display is connected or disconnected ?

• How to set up ?

• When you receive didDisconnectNotification

Change Your App’s Behavior

Handle connection changes with graceful transitions

3 Cores in iOS App

Recipe for Layout-Driven UI

• Find and track state that affects UI
• Dirty layout when state changes with setNeedsLayout()
• Update UI with state in layoutSubViews()

Animations with Layout-Driven Updates

• .beginFromCurrentState 👍👍👍

Animation API

• UIViewPropertyAnimator
• UIView closure API

UIGestureRecognizer

Discrete Gesture

• Start in the Possible state
• If they don’t pass go, they move immediately into the Recognized state
• These are useful for fire and forget interactions in your app
• But won’t tell you at every phase during the interaction ⚠️

Continuous Gestures

• Start in the Possible state
• They begin to be recognized, they move to the Begin state
• Receiving a continuous stream of events as the gesture moves around
• When the gesture is complete, it moves to the Ended state

UIPanGestureRecognizer

• Use translationInView( ) for dragging
• Use velocityInView( ) for animation handoffs

Get your app responsive quickly

Anatomy of a Launch

• Process Forking
• Dynamic Linking
• UI Construction
• First Frame
• Extended Launch Actions

Process Forking

• Man pages for fork and exec with POSIX ?? 😱
• iOS will take care of process forking for you 😆

Dynamic Linking

• 40~50 % of typical app launch time
  1. Allocating memory for execution
  2. Linking libraries and frameworks
  3. Initialization of Swift, Objective-C, Foundations, etc
  4. Static object initialization
• Best Practice ⭐️
  - Avoid code duplication
  - Limit use of 3rd-party libraries
  - Avoid static initializers

UI Construction

• Return quickly from 
  application(_:willFinishLaunchingWithOptions:)
application(_:didFinishLaunchingWithOptions:)
applicationDidBecomeActive(_:)
• Because UIKit waits for you to return from these functions 
  before we can mark your app as active 😱
• Avoid writing to disk & Avoid loading very large data sets
  Blocking, require a sys call
• Check database hygiene
  Clean data (core data), when you update your app 🛁

First Frame

• Core Animation renders your first frame
• Text drawing
• Image loading and decompression
• Only prepare the UI you need ⚠️
• Avoid hiding views and layer ⚠️
  Even when views and layers are hidden, they still have a cost.

Extended Launch Actions

• Prioritize loading content that should be visible at launch
• Design for poor network conditions

ABM (Always Be Measuring )

• Use Time Profiler to measure your launch
• Measure regularly
• Use statistical averages

Laser-Fast Launches

• Get responsive fast
• Use only what you need
• Measure, measure, measure

Why Is My App Slow ?

• 2 Solutions ( Computation, Graphics )

Solution 1: Computation

• UICollectionView and UITableview prefetching
• Push more work to background queues
  - Network and file system access
  - Image drawing
  - Text sizing

Solution 2: Graphics

• Complex Graphics
  - Visual effects (blur, vibrancy are expensive)
  - Masking

Smooth Scrolling

• Run Time Profiler and Core Animation instruments on your app
• Keep work off the main thread
• Use visual effects and masking sparingly

Continuing with Continuity

• Implement Handoff
• Delight your users
• Integrate with Spotlight search, Siri Shortcuts, and more

A Magical Experience

• Seamlessly transition activities between devices
• Work between iOS, macOS, and watchOS
• Doesn’t require an Internet connection
• It’s easy to set up !

How could you use Handoff ?

NSUserActivity

• Originating Device

• Continuing device
  - App must declare support for activity type
  - Implement these UIApplicationDelegate functions

Continuation Streams

• Set supportsContinuationStreams = true
• Call on the continuing device

• Call back on the originating device

Document-Based Apps

• Get this for free !
• UIDocument / NSDocument automatically create NSUserActivity objects
• Supports documents in iCloud
• Configure your Info.plist

Native App-to-Web Browser Handoff

• Set webpageURL property on the user activity
• Configure list of approved app IDs on web server
• Continuing app must opt in with an associated-domains entitlement

Web Browser-to-Native App Handoff

• Configure list of approved app IDs on web server
• Continuing app must opt in with an associated-domains entitlement

Debugging like a Pro

• The Detective Mindset
• Misplaced Views and view Controllers
• State issues
• Memory issues
• Xcode View Debugger and Memory Debugger
• LLDB expr and dump

Think like a Detective

• Verify your assumptions
• Look for clues
• Test your hunches
• Example

Loading a View or View Controller