iOSDev UK: Building Custom Controls with UIView

Rory Prior, ThinkMac Software, @roryprior

• generally subclass UIView directly
  • can subclass other controls, but things might not happen how you expect since lots of things happen in the background
  • and you may need to use private APIs…
• override methods:
  • initWithFrame for programmatic creation
  • initWithCoder for IB-created views
  • drawRect for actual drawing
• UIKit uses top left as origin
  • but CoreGraphics uses bottom left…
• adding UIImageView is easy
  • but quite heavyweight
  • instead can draw a UIImage directly
• similarly, can use UILabel or draw string directly
  • NSString drawAtPoint:withFont:
  • NSString drawInRect:withFont:
  • NSString sizeWithFont:
• drawing shapes:
  • CoreGraphics (nasty low-level C stuff :-) )
  • UIBezierPath (introduced in iOS 3.2)
• complicated graphics often still done better by using bitmaps — UIBezierPath can be processor-intensive for lots of lines
• UIColor can fill in patterns as well as flat colour

user interaction

• override UIResponder methods to detect touches
• you’ll need UIGestureRecognizers to detect swipes, pinches, etc
• but use sub-views of UIButton etc to make thins much easier
• see slides for nice example of adding UIResponder and UIGestureRecognizer
• use the delegate pattern to send feedback from your view to the rest of your app