Apresentação feita no barcamppt em Coimbra sobre as dificuldades encontradas na criação de uma aplicação para o iphone.

1. mekwa
from the web to the iPhone
@bncoelho

2. wtf is mekwa?

3. • a social network
• designed to meet new people
• flirting and dating

4. • http://www.youtube.com/watch?v=5Fbiu0FUoSk
designed to meet new people

5. • http://www.youtube.com/watch?v=PpLOud6OplQ
can be used for flirting and dating

6. how does it work?

7. • create a mekwa
• tell it your wishes
• you set off fulfilling other peoples wishes
• you feel good and meet new people

8. fulfill wishes?

9. • choose a desire to fulfill (ex: sushi on the
beach)
• take a bunch of pictures and text
• create an entry
• the owner of the mekwa decides if the
wish was fulfilled

10. why the iPhone?

11. • mobile was an original goal for the mekwa
project
• it was a good tech showcase
• could play a bit further with localization
• we all had iPhones

12. goals on the iphone

13. • fulfill desires on the go
• check other mekwas around me

14. what we needed
• to know the current location
• to create an entry(pictures + text)
• search for new wishes

15. everybody is doing it
how hard can it be?

16. really hard...
at least for us...

17. our background

18. • web developers
• no mobile experience
• no objective-c or cocoa experience
• nda just had been lifted, barely no
documentation

19. • application was ambitious
• maps, camera, network, website integration
• and... we had a month and a half to do it

20. how we did it...

21. mekwa api

22. • rails is api friendly
• used xml as a hash bag
• geokit made location aware functionality
easy

23. what? no xml?

24. • no easy way to parse an xml document
• we’re used to see objects as bags of
properties

25. libxml2 + custom wrapper

26. • we used libxml2 to parse xml
• built a wrapper to build diccionaries from
api responses

27. uploading stuff

28. • really low level
• ended up building http requests by hand in
order to add image data to the requests
body

29. maps?

30. • there is no maps api in the sdk
• we thought about abandoning feature

31. open source
to the rescue...

32. • we found route-me project
• support for MS VirtualEarth and
OpenStreetMap
• caches tiles on sqlite
• supports the drawing of custom markers

33. user interface

34. • table views are very versatile
• gets you up and running very quickly
• however...

35. ...they are a pain to
customize

36. • it’s not just drag’n’drop
• a designer can’t do it
• you have to code it
• we ended up pixel managing
• took a lot of work/time to
make them look nice

37. and was slow as a snail...
...but it was our fault

38. • cells are redrawn on demand
• images were being downloaded multiple
times
• scrolling was not smooth
• our answer was...

39. pre-load cache

40. • before loading each view we prefetched the
images needed.
• made loading a bit slower
• but scrolling was smooth
• at this point we didn’t have much time
• solution was a compromise

41. we had made it...
...barely

42. • at the end of our deadline we could:
• browse and accept entries
• search for wishes to fulfill
• create entries
• see other mekwas near us

43. it was an acceptable
prototype

44. ...but still had its share
of problems...

45. • crashed on a semi-regular basis (and that’s
being gentle...)
• it was still slow...

46. ...next steps
... improving for the AppStore

47. • the prototype was made in a collective
programming spree
• everything kinda worked but it was a
glorious mess

48. • the iphone has no garbage collector
• memory leaks are everywhere, releases
were missing
• iphone OS is merciless, it warns you the
first time and then it kicks you out
• crash!boom!bang!

49. memory leaks...

50. • objective-c memory model is based on a
reference counter
• alloc incs one
• release decs one
• on zero the object is deleted
• it’s pretty straight forward...

51. ...as long as you know
who owns object
...it was two very frustrating weeks...

52. app was stable enough...
... except when taking pictures

53. UIImagePickerController
is a memory hog...

54. check out the memory spikes
6mb each

55. • every time a picture was snapped, the
memory usage had a 6mb spike
• adding that to the lack of releases, three
pictures and the app was kicked out
• so be careful how you use it
• our solution involved using a singleton
instance of the image picker controller

56. as data grew...
prefetching was revealing itself painfully slow...

57. • technical debt caught us pretty fast
• we were showing 10 entries, each could
have 4 pictures
• wait for 40 pictures to download
• 1 minute until the app is usable
• it made you think the app was dead

58. ... use an activity indicator
...to show you app is not dead

59. how do you show an activity
indicator on the iphone?
hint: it’s not an animated gif...

60. ...background threads
that’s how you do it...

61. • it had never occurred to us to use threads
on the iphone
• sending time consuming tasks to a
background thread keeps the UI responsive
• every desktop software developer knows
that...

62. ... we had been stuck
in a webapp mindset for so long...

63. ...we didn’t realize
the iphone was a different beast...

64. • we used background threads to load all
images as they were needed
• and after some synchronization issues
resolved
• we had just had turbocharged our app

65. and it felt good...
you can find it in the app store

66. ...lessons learned
...almost all of them the hard way

67. • iphone apps are similar to desktop apps
• but with memory capabilities from 10 years
ago
• design is hard, not just drag and drop, you
have to code it
• threads speed up you app

68. • UIImagePickerController is a memory hog
• there was no maps api used route-me
• networking is really low level
• xml parsing is really low level

69. • http://www.youtube.com/watch?v=GjyKWiwTRxY

70. shameless plug
...so if you need an
iphone app
don’t hesitate, contact us at www.rupeal.com

71. interesting references

72. • www.mekwa.com
• http://code.google.com/p/route-me/
• http://blog.airsource.co.uk/index.php/2008/11/12/memory-usage-in-
uiimagepickercontroller/
• http://joehewitt.com/post/the-three20-project/
• http://stackoverflow.com/questions/441345/does-uiactivityindicator-require-
manual-threading-on-iphone
• http://www.hackdiary.com/2009/01/26/switching-from-scripting-languages-to-
objective-c-and-iphone-useful-libraries/

73. • http://www.youtube.com/watch?v=GjyKWiwTRxY
• http://www.youtube.com/watch?v=5Fbiu0FUoSk
• http://www.youtube.com/watch?v=PpLOud6OplQ

74. ???