Performance on iOS and watchOS

Why should I think about performance?

It’s a feature in your app that you should have on your mind all the time:

• Responsiveness delights and engages users

• Be a good neighbor, especially in Multitasking on iPad

• Efficient apps extend battery life

• Supports the whole range of iOS 9 hardware

Thinking About Performance

• Choosing technologies

  • Know the technologies

  • Pick the best ones for your app

  • Apple technologies are optimized (we use them)

  • Benifit from updating

• Taking measurements

  • Animations: Instruments: Core Animation

  • Responsiveness: Core instrumentation, Instruments: System Trace - Don’t ship your instrumentation: Create a copy of release scheme in Xcode, and define one additional define, so you could build a release version of the app with performance instrumentation quickly and easily. - Collect start and end times: CFAbsoluteTimeGetCurrent - Taps and button presses: IBAction, touchesEnded, UIGestureRecognizer target - Tabs and modal views: viewWillAppear, viewDidAppear, will show how long it takes to display a the view.

• • Memory: Xcode debugger, Instruments Allocations, Instruments Leaks

    • Allocate, Reallocate memory takes time.

      • Ref: iOS App Performance: Memory, WWDC12

      • Ref: Improving Your App with Instruments, WWDC14

      • Ref: Optimzing Your App Multitasking on iPad in iOS 9

• Setting goals

  • 60fps scrolling and animations.

  • Respond to user actiosn in 100ms

• Performance Workflow

  • Reproduce -> Profil -> Measure -> Change code -> Reproduce

  • Profiling vs Measuring

    • Profiling: Unsderstanding overall app activity

      • Xcode debugger

      • Instruments: Time Profiler

• • • Measuring: Instrumenting a specific action

      • CGAbsoluteTimeGetCurrent

      • Instruments: System Trace

• • Avoid Using the Main Thread for

    • CPU-intensive work

    • Tasks that depend on external resource

• • Common Blocking Calls

    • Any code path that ends up making a syscall

    • Accessing resources not currently in memory: Disk I/O, Network access

    • Waiting for work to complete on another thread

• • • Networking: NSURLConnection and friends

      • Use asynchronous API

      • Use GCD, Ref: Building Responsive and Efficient Apps with GCD

      • NSURLSession background session

• • • Foundation initializers

      • contentsOfFile:

      • contentsOfURL:

• • • Core Data

      • Move some Core Data work to different concurrency modes. Ref: What’s New in Core Data, Mission.