mekwa
from the web to the iPhone
@bncoelho

wtf is mekwa?

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

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

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

how does it work?

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

fulfill wishes?

• 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

why the iPhone?

• 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

goals on the iphone

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

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

everybody is doing it
how hard can it be?

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

our background

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

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

how we did it...

mekwa api

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

what? no xml?

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

libxml2 + custom wrapper

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

uploading stuff

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

maps?

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

open source
to the rescue...

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

user interface

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

...they are a pain to
customize

• 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

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

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

pre-load cache

• 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

we had made it...
...barely

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

it was an acceptable
prototype

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

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

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

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

• 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!

memory leaks...

• 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...

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

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

UIImagePickerController
is a memory hog...

check out the memory spikes
6mb each

• 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

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

• 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

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

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

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

• 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...

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

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

• 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

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

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

• 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

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

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

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

interesting references

• 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/

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

???