iOS dev notes

iOS dev notes

WWDC 2013 - #???: What's new in Foundation Networking
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. NSURLConnection, configured through NSURLRequest. Has a global storage for cookies, cache, etc.
. NSURLSession, replaces NSURLConnection, per object configurable.
. Uploads/Downloads through the filesystem. Can be done Out-of-process, but not a regular data request.
. NSURLSessionTask per request, represents the status and progress. Cancel, Suspend, Resume.
. Per session policies: cache, cookies, credentials.
. backgroundSessionConfiguration
. Background Transfers


WWDC 2013 - #203: What's new in Cocoa Touch
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. NSURLSession replaces NSURLConnection.
. UIView tintColor, affects all subviews.
. new key frame animation: animateKeyFramesWithDuration:...
. UIViewController.wantsFullScreenLayout deprecated! is YES all the time.
. UIExtendedEdge is UIExtendedEdgeAll by default.
. preferredContentSize, will be used all over in iOS 7, useful for subViewControllers.
. UIStatusBarStyle only affects text, since background will be always transparent.
. Custom Transitions, check transitionDelegate, called when/how.
. State Restoration...
. UIDynamicBehavior: fluid responsive animations, behaves like a tree, they can be nested. Attachment, collision, gravity, push, snap.
. Dynamic Text, preferredFontForTextStyle: THIS method is very very important.
. NSTextContainer, NSLayoutManager, NSTextStorage.


WWDC 2013 - #206: Getting Started with UIKit Dynamics
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. content is king.
. core animation, UIView, motion effects (parallax).
. UIDynamicBehavior contains views.
. UIDynamicAnimator contains UIDynamicBehavior (which are composable and subclassable).
. translatesReferenceBoundsIntoBoundaries.
. addBoundaryWithIdentifier:fromPoint:toPoint:.
. snap: move interpolating to a position and leave it without rotation.
. friction, resistance, elasticity, density, allowsRotation.
. add angular or linear velocities from a gesture.
. UIDynamicItem protocol: center, bounds, transform.
. CollectionViewLayoutAttributes.
. you can initialize an animator with a layout.


WWDC 2013 - #202: Advanced Techniques with UIKit Dynamics
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. UIDynamicAnimator detects when the system rests and stop computing.
. UIDynamicAnimator just changes 'center', will not be aware if center, bounds or transform changes externally. In this later case, remove and add the behavior again.
. CollectionViews... 3 ways to use dynamics:
	- specific animation: create an animator and discard it later.
	- animate a subset.
	- build an entire layout: use it for small data sources!
. UIDynamicAnimator:layoutAttributesForCellAtIndexPath
. continue on min 23...


WWDC 2013 - #210: Introducing Text Kit
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. Fast modern text layout and rendering engine.
. Built on top of Core Text.
. All text-components were re-written on top of text kit.
. paginated layouts, texts in columns, rich text, exclusion paths.
. text folding, custom truncation.
. Kerning and Ligature ON by default!
. Dynamic Type: small, medium, large
. Font descriptors.
. Symbolic traits: regular, bold, italic, expanded, constraint, line spacing, etc.
. NSTextContainer: coordinate system and geometry.
. NSLayoutManager...
. Glyph: one or more characters on screen.
. Any kind of custom links on the texts!
. Text attachments... you can add photos and text will adapt.
. [myFont lineHeight] whole line.
. [myFont capHeight] from the base (no cuenta el palito de la 'g' por ejemplo).
. [myFont leading] space between lines.
. UIContentSizeCategoryDidChangeNotification: invalidate intrinsic content size by resetting the font if using auto-layout.


WWDC 2012 - #219: Advanced Collection Views and Building Custom Layouts
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. UICollectionViewLayoutAttributes: one per view and has the attributes: center, size, alpha, transform, zIndex
. The Extensible Delegate: UICollectionViewDelegateFlowLayout extends UICollectionViewDelegate, you can set the delegate to the view collection, and it will call the appropriate new methods.
. -invalidateLayout when the model changes or implicit invalidations with performBatchUpdates:completion:
. pinch resizing gesture.
. going fully custom (no FlowLayout subclass), when you want something no grid like.
. order of operations (fully custom): prepareLayout, collectionViewContentSize, layoutAttributesForElementsInRect


WWDC 2012 - #202: Introduction to Auto Layout
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. constraint-based layout system.
. Visual Format Language: constraintsWithVisualFormat:
. constraints has priorities!
. layout process is bottom-up.
. po [[UIWindow keyWindow] _autoLayout] to see if there is something AMBIGUOUS.
. translatesAutoresizingMaskIntoConstraints


WWDC 2011 - #121: Understanding UIKit Rendering
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. CoreAnimation uses pixels (640x960), not points! so try to do calculations on UIKit.
. Frame changes with transformation! but not the bounds nor center. This happens because frame is a calculated property.
. view.center = layer.position
. view.center = layer.affineTransform
. layer.transform is for 3D.
. layer.anchorPoint ;)
. view.layer.contents should not be touched directly.
. drawRect: consumes memory because it needs to generate a drawing buffer, be careful and try to use UIImageView instead.
. CATransaction is implicit used when changing properties of views and commit when run loop is complete.
. Avoid offscreen rendering: it's when can't draw directly to the framebuffer.
. Layer rasterization: when doing offscreen rendering BUT you're sure the view's content won't change and you tell the system to cache the drawing.


WWDC 2012 - #238: iOS App Performance: Graphics and Animations
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. drawRect: string and image drawing is slow.
. call setNeedsDisplay only when needed.
. avoid overriding drawRect: for instance UIRectFill is slower and consumes more memory than view.backgroundColor.
. try to use drawRect: with the rect and setNeedsDisplayInRect: in the same way.
. when using images, try to use UIImageView since it can use CGImage data directly, not the case for drawRect: that has to create a backing store for it.
. image decoding or drawing, try to do it in the background.
. PNG and JPEG, not other formats, they are not optimized for iOS.
. view.layer.drawsAsynchronously, GPU drawing, high setup cost, high memory hit, good for lots of drawing into a single view.
. when drawing over and over above a background, you can merge each new draw to the background and reuse that view to use for the next draw, kind of accumulative drawing. Core Graphics to the rescue.
. when having a performance problem, you have to see if it's CPU bound or GPU bound.
. 100% device usage is a sign of GPU bound.
. to reduce view composition, use flattening, which means reducing hierarchies and use more CPU than GPU.
. flattening hurts responsiveness because of the up-front CPU usage.
. flattening means to implement drawRect: and avoid view hierarchies and that way increase smoothness at the cost of responsiveness.
. view.layer.shouldRasterize: another way to decrease usage of GPU.
. offscreen rendering: when doing masking and clipping, it will happen.
. check 'Color hits Green and Misses Red' to see if shouldRasterize is working.


WWDC 2012 - #242: iOS App Performance: Memory
---------------------------------------------

. avoid running long tasks on main thread, because memory warnings happens there, and that way they can't be delivered.
. UIViewController viewDidUnload -> use that no more.
. avoid spikes of memory, you can use autoreleasepool to avoid that.
. take heap snapshots (Mark Heap) and see how heap grows when repeating actions. e.g: going back and forward into a view controller.
. take a look a reference counting history.
. zombies template on iOS simulator, intercept messages to deallocated objects.

WWDC 2012 - #236: Evolution of View Controllers
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. add: first add child VC to parent, then subview to view, then tell child it was moved to parent.
. remove: first tell child it was moved to parent 'nil', then remove subview, then remove child VC from parent.
. parents make the rules and children follows.
. layout is independent of interface orientation *.
. VC containment: many VC on the screen at once.
. VC containment forwards appearance methods.
. * VC containment allows child VC not to rotate if they do not want, even if parent rotates.
. view*unload is deprecated since is not needed for performance reasons anymore, you can use didReceiveMemoryWarnings in case of unloading resources.
. updateViewConstraints: to layout views...
. VCs have state restoration in case they are killed.
. [window setRootViewController:] to receive rotation calls...
. a VC should never set its own frame.


#409: Learning Instruments
#706: Networking Best Practices
#506: Optimizing 2D Graphics and Animation Performance
#601: Optimizing Web Content in UIWebViews and Websites on iOS


AutoLayout
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. setTranslatesAutoresizingMaskIntoConstraints is used when creating UIViews manually
. self.edgesForExtendedLayout = UIRectEdgeNone not to go full screen
. topLayoutGuide and bottomLayoutGuide to indicate top and bottom offsets of areas that should not overlap


Core Data
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. one context per thread
. OR context + store per thread, more memory but less locking code areas and harder to communicate changes between contexts.
. if using != context, you must pass objects by the ID and the request the whole object from that thread.
. @synchronized(self) {}

Drawing
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. CALayers do not have touch support
. CALayers:setContentsScale must be used for self created layers
. (CGSize)intrinsicContentSize (which should call systemLayoutSizeFittingSize:) is very important with auto layout


Foundation
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. do not use isKindOfClass: for class clusters, an inmutable class could report is mutable and things like that.


iPad version
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universal -> 1 target and 2 resources dir
specific -> 2 targets

auto-sizing! essential, use anchor or proportional size increase

on ipad -> UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad

user availability macros to target lower iphone sdks and if ([newerClass class]) {} (must-use LLVM and Clang) or NSClassFromString (prior 4.1 sdk). Also instancesRespondToSelector:

Default-Landscape.jpg and Default-Portrait.jpg

UISupportedInterfaceOrientations in Info.plist

CFBundleIconFiles in Info.plist

Support both variants of an orientation!!! si solo corre en landscape, que corra en la otra variante tambien (arriba/abajo)


Error Handling
--------------

domain -> posix, mach, cocoa, webkit, xmlparser, etc.
code -> specific domain code error (search for headers)

NSError for user level errors.
NSException for programming errors.


Views
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UINib to load views made with IB that are not associated to a view controller.
LayoutSubviews should be used when autosizemasks are not enough


Threads
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. NSOperation can cancel, set number of concurrent operations and create dependencies.
. GCD queues should use dispatch_retain/dispatch_release when are passed around.
. GCD queues can be suspended.
. semaphores to to specify certain amount of resources available.
. group of queues so you can wait for all of them to finish.