Reactive cocoa 101改

ReactiveCocoa 101改
Hai Feng Kao
1

Object-Oriented Programming
● 封裝、繼承、多型

Functional Programming
● Lambda Calculus
● Functions without side effects
● Programs as function
compositions (y = f(g(h(x))))

Functional Reactive Programming
● In functional programming, things get hard
because functions can’t have side-effects
o Every time a function is called, it must
return the same y for same x
o y = f(x)
● In functional reactive programming, time is
an implicit parameter (no monads)
o y = f(x, t)

ReactiveCocoa
● A open source FRP framework developed
by Github
o iOS / OSX
o MIT License
o 3.0 supports swift
o https://github.com/ReactiveCocoa/Reacti
veCocoa

Signals
● Primary data source of FRP
● Signals send values over time until they
complete
o A signal never sends anything after
completing or erring
o A signal either completes, or errors out,
but never both

Signals(cont.)
● A signal has no concept of a “current
value” or “past value”
● It’s like a pipe
● Signals can be chained to transform the
values
o This is core to FRP: data transformation
of values sent over time
o y = f(g(h(x)))

RACSignals
● always send id, not primitives
o NSInteger -> NSNumber
o CGRect -> NSValue

● The building blocks of functional world
o map, reduce, filter

Map
● Mapping performs a value transformation
on the given signal
o It ”maps” each value sent along the
signal to a new value
o It then passes that new value along,
creating a new signal

● Combines two or more signals’ values into
one
o Useful for waiting for conditions to be
met
o Useful for deciding between values
Reduce

Filter
● Filtering allows values that pass some test
to “pass through”

● The building blocks of functional world
o map, reduce, filter
USELESS?

Bindings
● Bindings can bind a property to the latest
value sent on a signal
● All bindings created with the RAC macro
are one-way
● Bindings are the secret sauce that hold
apps together

Imperative vs Functional
Imperative:
Functional:

MVC (Model View Controller)
26
ModelView Controller
Input
Update
Update
Notify

MVC (Model View Controller)
• Pros :
• Independent module
• Reusable model
• Cons:
• too may files
• hard to write unit test
• controller need to access view&model
27

MVVM(Model View ViewModel)
29
ModelView ViewModel
Input Update

• Pros:
• ViewModel can be unit tested
• ViewModel has no access to view
• Model has no access to ViewModel
• View is simple
• UI logic moved to ViewModel
• Cons:
• hard to debug
• performance hit!!! 30

31
ModelView ViewController ViewModel
ReactiveCocoa

Reference
● Ash Furrow Reactive Cocoa 101
o https://www.youtube.com/watch?v=TlgU
WYrQ0sc
● Functional Reactive Programming on iOS
o https://leanpub.com/iosfrp/

Reactive cocoa 101改

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