iOS  Best  Prac-ces:  Avoid  the  Bloat  

Twi7er:  @JAgostoni  h7p://jason.agostoni.net  

h7p://bit.ly/SportsApp  

Jason  Agostoni  

•  Sr.  SoBware  Architect  at  CEI  – Lead  for  Integra-on  and  Mobile  Areas  

•  14+  Years  in  MicrosoB  and  Mobile  PlaMorms  •  Apps  in  the  App  Store:  – Pi7sburgh  Code  Camp  – Sports  Schedules  (give  me  a  good  review?)  

•  h"p://bit.ly/SportsApp  – Several  clients’    apps  

•  Clients  of  all  sizes  

Challenges  

•  We  have  learned  to  apply  best  prac-ces  and  design  pa7erns  for  RIA/Rich/Web  apps  

•  Why  is  mobile  different?  – Symptom  of  learning  on-­‐the-­‐side?  

– Feeling  that  it  doesn’t  ma7er?  – Less  experienced  developers?  

•  It  may  be  even  more  important  to  apply  best  prac-ces  in  mobile  development  

DO  YOU  BELIEVE  IN  BEST  PRACTICES  AND  DESIGN  PATTERNS?  

Ra-onale:  Best  Prac-ces  

•  Avoid  common  mistakes  •  Consistency  •  Security  •  Maintainability  

•  Etc.  

WE  ALL  KNOW  ABOUT  BEST  PRACTICES  IN  SOFTWARE  DEVELOPMENT:  WHY  DO  WE  SEE  THEM  ONLY  IN  POWER  POINT  PRESENTATIONS?  –  Prakash  J  

Ra-onale:  Design  Pa7erns  

•  Most  problems  have  already  been  solved  •  Easy  to  recognize  by  developers  •  Nearly  all  frameworks  embrace  pa7erns  

•  Tested  over  and  over  again  •  Not  just  reusable  code  but  reusable  ideas  •  Reduce  implementa-on  -me  

Big  Ball  Of  Mud  

•  Very  common    an--­‐pa7ern  in  Objec-ve-­‐C  

•  Makes  code  un-­‐maintainable  

•  High  code  risk  •  Insecure  •  Ugly  

The  Ugly  App  

•  It  ain’t  pre7y  •  It  has  lots  of  problems  •  It’s  unmaintainable  

•  It’s  fragile  •  It’s  full  of  risk  •  Worst  yet:  It’s  not  atypical  

•  It  can’t  be  that  bad  …  can  it?  

 

Complexity  Indicators  

•  More  than  one  protocol  in  a  class  •  Large  number  of  proper-es  (not  a  model)  

•  Direct  references  between  views/controllers  •  Lots  …  and  lots  …  of  scrolling  •  Long  list  of  #import  statements  

•  Really  long-­‐winded  methods  

Problem  #1:  Responsibili-es  

•  AppDelegate  has  TOO  many  responsibili-es  – Holds  a  reference  to  the  Data  Model  – Responsible  for  loading  the  data  model  

– Responsible  for  parsing  the  XML  – Responsible  for  being  the  AppDelegate  

•  Each  class  has  to  reference  the  delegate  and  has  control  over  the  data  source  (NSMutableArray)  and  can  corrupt  it  

Solu-on:  Two  Pa7erns  

Singleton  

•  Encapsulate  control,  life-me,  scope,  crea-on  of  an  object  

•  Ensure  only  one  copy  of  an  object  exists  

•  Perfect  replacement  for  “global  variables”  in  the  App  Delegate  

•  Ugly  App:  the  data  source  

Single-­‐Responsibility  Principle  •  Any  class  should  have  at  

most  ONE  purpose  •  A  class  should  completely  

encapsulate  that  purpose  •  A  class  should  have  only  

one  “reason  to  change”  •  Cohesiveness  •   Ugly  App:  Split  the  XML  

parsing  from  the  data  model    

Singleton  in  Objec-ve-­‐C  •  Shared  Manager  

•  Instance  Variables  

•  Convenience  Methods  

FIX  #1:  SPLIT  OUT  THE  DATA  AND  XML  RESPONSIBILITIES  

Problem  #2:  Class  Coupling  

•  Too  many  classes  have  direct  references  •  All  classes  rely  on  AppDelegate  making:  changes  are  HIGH  impact  

•  Different  views/ViewControllers    refer  to  each  other  (BAD)  

•  Change  is  DIFFICULT  

AppDelegate  -­‐  Model  -­‐  XML  

Dash  View  /  Controller  

List  View  /  Controller  

Solu-on:  Observer  Pa7ern  

•  Model  updates  are  coordinated  through  events  bubbled  to  concerned  views  

•  “Publisher”  pushes  event  to  a  central  framework  –  publish/subscribe  

•  “Observers”  listen  for  specific  events  to  take  ac-on,  data  are  frequently  packaged  in  event  

•  No  direct  coupling  is  necessary  between  publishers  and  observers  

Observer  in  Objec-ve-­‐C  

NSNoMficaMonCenter  •  Broadcast  between  objects  

within  an  applica-on  •  Each  NSNo-fica-on  as  a  

name,  sender  and  info  dic-onary  

•  Observers  use  the  addObserver  method  to  route  no-fica-ons  to  a  given  method/selector  

•  By  default,  no-fica-ons  are  routed  synchronously  

Observer  in  Objec-ve-­‐C  

Key-­‐Value  Observing  

•  Observers  are  automa-cally  no-fied  when  a  property  changes  on  an  object  

•  Subject  must  be  “KVO”  compliant  

•  Subject  can  be  single  object  or  collec-on  

h7p://developer.apple.com/library/mac/#documenta-on/cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html    

FIX  #2:  DECOUPLE  THE  VIEWS  USING  AN  OBSERVER  PATTERN  

Improvements  

•  Using  these  design  pa7erns:  – The  applica-on  is  more  maintainable  – Code  risk  is  greatly  reduced  – The  code  is  easy  to  follow  and  understand  – There  is  less  impact  to  change  

•  Other  Developers  will  appreciate  it  – The  code  is  intui-ve  – The  design  pa7erns  are  recognizable  

Built-­‐in  Design  Pa7erns  

•  Model  View  Controller  –  Presenta-on  pa7ern  na-ve  within  CocoaTouch  

•  Category  –  Provides  ability  to  extend  func-onality  of  a  class  without  subclassing  

•  Delega-on  (Protocols)  –  Same  as  interfaces  in  other  languages  

•  Proxy  (NSProxy)  –  Stand-­‐in  object  which  forwards  calls  to  another  object  

•  Factory  –  Object  which  creates  other  objects  

–  Interes-ng  in  Objec-ve-­‐C  where  the  Classes  themselves  have  factories  

Resources  

•  Books  –  Cocoa  Design  Pa7erns  Buck,  Yacktman  Addison  Wesley  

–  Pro  Objec-ve-­‐C  Design  Pa7erns  Carlo  Chung  Apress  

•  Online  – My  Blog  

h7p://jason.agostoni.net  

–  Objec-ve-­‐C  Design  Pa7erns  h7p://www.informit.com/ar-cles/ar-cle.aspx?p=1566875  

– Wikipedia  •  Has  some  good  examples  in  the  general  design  pa7ern  pages  

Thanks!  

•  Twi7er:  @JAgostoni  •  Blog:  h7p://jason.agostoni.net  

•  Sports  Schedules:  h7p://bit.ly/SportsApp  

•  Code  samples:  h7ps://github.com/JAgostoni/iOS-­‐Best-­‐Prac-ces