IPhone Tech Talks/Advanced UIKit and Device Features

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Matt Drance (mdrance@apple.com)


  • Animation, text input, interruptions, URL communication
  • Address book, movie player, camera and photo library

Contents

[edit] Animation

  • everywhere on iphone, each UIView has a Core Animation layer
  • size and pos, opacity, and transitions

[edit] Animation blocks 

[UIView beginAnimations:@"scaleDown" context:nil];
[UIView setAnimationDuration:1.0];
// view changes are done here
[UIView commitAnimations];

[edit] Text input/output

  • output is easy, use UILabel, UIWebView, NSString (UIStringDrawing)
  • input easy too! use UITextField, UITextView

[edit] Keyboard

  • customize in Interface Builder or UITextInputTraits
  • shown programmatically with becomeFirstResponder (if you, say, wanted it to show up on viewDidAppear)
  • hide with resignFirstResponder call (focus/blur from JavaScript, essentially)
  • UIWindow notifications
    • UIKeyboardWillShowNotification
    • UIKeyboardWillHIdeNotification
    • they include keyboard dimensions, use this to place stuff right next to keyboard etc.
  • powerful delegate model
  • autocorrection occurs very late - wait for textFieldDidEndEditing
  • have an exit strategy
    • cancel/done button
    • implement textFieldShouldReturn
    • built in UISearchBar support - showsCancelButton = YES


[edit] Handling interruptions

  • can come at any time
  • phone call, SMS, Calendar alert
  • applicationWillResignActive:
  • preserve application state, pause audio/graphics/animations
  • if user dismisses, applicationDidResumeActive: fires
  • if user accepts interruption, applicationWillTerminate: fires (like home button press) - potential data loss! deal with this!!!

[edit] URL Communication

Opening External URLs: 

NSURL *url = [NSURL URLWithString:urlString];
[[UIApplication sharedApplication] openURL:url];
  • will quit when called, as another app will handle the URL
  • http, https, feed - Safari
  • mailto - Mail
  • Google Maps
  • YouTube
  • Phobos.apple.com for appstore/itunes

Can declare your own URL types

  • done via Info.plist - CFBundleURLTypes array

Receive URLs via application delegate - handleOpenURL, then get and parse the query string

  • secure your URL handlers! don't provide an API for everything under the sun!

[edit] Address Book

  • full read/write access!
  • reusable view controllers too
  • ABPeoplePickerNavigationController
  • ABPersonViewController
  • ABNewPersonViewController
  • ABUnknownPersonViewController

[edit] Presentation

  • present modally, as is a navigation controller - will have two nav bars if you push on top of existing
  • add person controllers to a navigation controller

[edit] Movie Player

  • H.264 Baseline @ 640x480 max
  • always in landscape orientation
  • start/stop with loaded/finished notifications
  • static only, no streaming via RTSP :-(

[edit] Camera and Photo Library

  • UIImagePickerController
  • access camera and photo library
  • check for camera via isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera (iPod touch doesn't have one)
  • present modally ([self presentModalViewController:picker animated:YES];)
  • didFinishPickingImage with editingInfo (original image, rectangle that was selected via crop/zoom)
  • see Photo Tagger app! useful!
  • load images on demand
    • use imageWithContentsOfFile: instead of imageNamed: - allows direct control of image memory allocation (imageNamed system caches it)
  • use PNGs, if at all possible
  • scale to optimal size using drawInRect: to reduce memory load (camera images are 1600x1200!)

[edit] Saving images

  • can save any image to the photos album
  • UIImageWriteToSavedPhotosAlbum
    • adds to Camera Roll on iPhone, Saved Photos on iPod touch
  • can save locally, too, for caching etc. in sandbox
  • can use renderInContext:UIGraphicsGetCurrentContext() to take screenshot of a view

[edit] Multi-touch

  • one of the few cases you'll subclass UIView

[edit] single-touch

  • implement touchesBegan:withEvent: (get array with all UITouch sources)
  • implement touchesMoved:withEvent: (fires repeatedly on moving)
  • implement touchesEnded:withEvent: (when lift finger)

[edit] single-tap / double-tap

  • UITouch has a Tap Count (1/2)

[edit] multiple-touch

  • same implementation, just more information
  • second finger calls touchesBegan again, now get two UITouch objects (if one finger isn't moving, phase is 'Stationary')
  • see Touches sample code

[edit] detecting a swipe

  • get starting point in touchesBegan
  • track motion in touchesMoved
    • straightish?
    • dragged far enough?
    • dragged quickly enough?

[edit] Accelerometer

[edit] three-axis data

  • x-axis is counterintuitive, left is positive
  • use for interface orientation, device orientation, analog user input (games!)

[edit] analog data

  • 10-100 hertz approx range
  • 30-60 for games, generally
  • callbacks should be lean, so queuing doesn't happen
  • use filters to remove noise (see BubbleLevel sample)

[edit] Core Location

[edit] Location Sources

  • cell triangulation
  • wireless access points
  • GPS
  • single API
  • CILocationManager
  • set up distanceFilter and desiredAccuracy ('let me know when I've moved 3km')
  • location updates give previous and current location
  • check timestamps to avoid cached data (think Twinkle thinking you're still in Rochester when you're in Buffalo)
  • new in 2.2 - direction and speed updates

[edit] Privacy

  • location prompt on first use of startUpdatingLocation (and every other use unless say OK)
  • plan for kCLErrorDenied
    • locationManager:didFailWithError:
    • kCLErrorDenied - user said don't allow, stop asking until next launch?
    • kCLErrorLocationUnknown - often temporary, keeps trying until stopUpdatingLocation

[edit] Battery life

  • use a 30 second timeout
  • try to use minimum accuracy possible - saves battery
  • stop updating and release when finished
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