^3.0 coming which will deprectate some of this ^Work on 3.0 was in progress when Swift was introduced, the new 3.0 will see most reimplemented in Swift, with bridging headers for use from Objective-C
- Functional reactive programming framework for ObjC
- Currently 2.3.1
- Inspired by Reactive Extensions
- Alternative to traditional KVO paradigm / completion block as last argument
- Created by GitHub & used in GitHub for Mac (Hi Coby!)
^Macros help with short-handing common patterns as we'll see
^Categories on existing classes, including UIKit
^Signals conform to ARC etc
- Handy macros
- Handy categories
- Good memory management semantics
- Tuples!
- Handle asynchronous / event-driven data sources
- Chain dependent operations
- Parallelise independent work
- Simplify collection transformations
- Manage and minimise state
^ We'll build a simple login form with validation and show how the UI can respond dynamically to user input, then submit the form via a network request.
- Login form
- Field validation
- Dynamic UI
- Network request
Represents an event source, or stream of values delivered over time.
Three types of event:
- Next (Value)
- Error
- Completed
^ Mention subscribeNext:
^ Discouraged to explicitly subscribe - use RAC macro
^ Wide selection of operators that often can accomplish what you want instead
Each event for a signal is delivered to its subscribers.
Most often used is subscribeNext:
It takes a block which is executed for every value received
^ UIKit is mostly not KVO compliant, RAObserveing the text property on UITextField won't work
This is like KVO but for common UIKit elements!
ReactiveCocoa provides categories to help like rac_textSignal for UITextField
Let's see how this works...
^ tag: 1
^ Form validation
^ Signals are lazy (or cold), so you can compose everything before running it
Lots of signal operations available (map, filter, skip, take, ignore, collect, to name a few)
We can use map: to help with form validation
^ Map takes a transformation block which is applied to each value sent on the signal ^ In our example we'll examine the content of the email text field and map it to a BOOL representing its validity
Map NSString to an NSNumber representing a BOOL
- UI state management
- User feedback
- Compact logic
^ RAC is a shortcut macro which allows updating a property on an object with values sent on a signal ^ RACObserve performs KVO on a property and returns a signal of all values resulting from property changes
Macros like RAC() are handy shortcuts for UI state management
Logic automatically updates UI
Like CocoaBindings for iOS and Mac
^ tag: 2
But what about validating the form as a whole?
The operator combineLatest:reduce: helps
^ combineLatest: takes an array of inputs signals, and returns a signal that when any input signal sends a value sends a tuple containing the latest value sent by each.
^ Could use map: and receive and unpack a tuple to operate on.
^ This is a common use case though, combineLatest:reduce: will take a block with as many arguments as input signals
The combineLatest: operator takes an array of signals
So, reduce: maps a tuple to block arguments
^ tag: 3
Combined validation is a common pattern
ReactiveCocoa offers methods for boolean signals
Let's rewrite our form validation...
^ if:then:else
ReactiveCocoa offers lots of logic as signals
- and
- or
- not
- switch:cases:default:
- if:then:else:
^ tag: 4
^Ok, so notification center has blocks but still...
-
UIControlEvent
[UIControl rac_signalForControlEvents:] -
RACCommand
UIButton,UIBarButtonItem,UIRefreshControl,rac_commandproperty
-
Timers
[RACSignal interval:onScheduler:][RACSignal delay:] -
NSNotificationCenter
[NSNotificationCenter rac_addObserverForName:object:] -
@weakify/@strongifymacros are helpful
^Many more available, e.g. action sheets ^We'll probably get a solution for the return-value-delegate-type issue in 3.0
For example:
- UIGestureRecogniser (
rac_gestureSignal) - UIAlertView (
rac_buttonClickedSignal) - Note: can't be used if delegate method returns a value 😔
^ tag: 5
^Or a background process that must write files, delete duplicates and then upload
Chaining dependent, asynchronous operations allows for streamlining complex tasks
E.g. a network operation that needs to do a number of fetches
^ tag: 6
^ Disposables are related to subscriptions ^ They encapsulate any clean-up necessary when a signal is being torn down (through error, completion or unsubscription) ^ From the previous examples, removing KVO or notification observers added. ^ A signal delivering the results of a network request would cancel the request
A subscription wraps a number of disposables
Can be useful for cancelling any ongoing work.
E.g. cancelling an ongoing network request.
^ tag: 7
^ Underscore AND RAC - Why not use both?
- Some other libs provide collection operations, e.g. Underscore
- Working with signals allows for chaining though
- Filtering, mapping etc.
- Collections are treated as streams
- Lazily executed
^Timers: the timing aspect seems well suited but not for precision
Some places, ReactiveCocoa doesn't offer huge benefit as it requires additonal management
E.g. table view cell reuse & timers
And no Swift support... yet.
^ Many efforts to bring existing frameworks into the reactive world, replacing delegates with signals, etc
^ Core Data - ReactiveCoreData ^ HTTP client - AFNetworking-RACExtensions ^ ReactiveCocoaLayout - A work in progress with an interesting approach / alternative to auto layout, using signals and operations to express layout changes, animations etc
- HTTP (AFNetworking-RACExtensions)
- Core Data (ReactiveCoreData)
- Core Bluetooth (ReactiveCoreBluetooth)
- Layout (ReactiveCocoaLayout)