Iphonelite3

First app using iPhonelite3

iphonelite3 — Thu, 30 Apr 2009 14:47:00 +0000

My first app based on iPhonelite3 is out WindSesh. Contact me if you want a Promo code, with the current feature set it is mostly useful for its intended audience. Check the web site for details.

UITableView and sqlite3

iphonelite3 — Thu, 30 Apr 2009 14:39:16 +0000

After about 20-30 entries displaying a table directly out of the database does not work anymore. The UI is not smooth and you can feel the load time. Need to cache in memory.

Having an id member

iphonelite3 — Sun, 15 Mar 2009 05:46:44 +0000

On the server side of my soon to be released application (haha), I have an id field in all my tables. This is the foreign key used by all the relationships. On the iPhone id is a type and although it can also be a variable name I avoided using it in my initial implementation of the code. Instead I use _id for the sqlite3 tables and the mapped objects.

This is an inconsistency that has been nagging me since the first day on this project. I will likely try to eliminate it by moving the iPhone code to also use id as the variable name. This is just a heads up for now.

Also coming soon some initial implementation of delete with where arguments, currently only delete of all the records is implemented.

Gis extensions, not

iphonelite3 — Sun, 01 Mar 2009 16:53:19 +0000

It seems there are starting to be some GIS extensions for sqlite3, one of the promising one being Spatialie. However this requires Sqlite version 3.6.2 and that is not available on the iPhone at this time.

My current data requirements are in the thousand of records and hopefully there is enough CPU power to handle this without spatial indexes. I am considering adding some new classes based around a Lite3Predicate to help with GIS related functionality.

GTM Test

iphonelite3 — Wed, 11 Feb 2009 07:55:37 +0000

I moved the GTM Test support files under Lite3/GTMTest to allow for easier integration in new projects. You still need to

create an Unit test target
make sure that the Unit test files are associated only with the new target (otherwise you get a link error about having to _main functions then)
define ALog in the precompiled header file and define -DDEBUG as other OTHER_CFLAGS
add sqlite3 to the project

#ifdef DEBUG # define DLog(...) NSLog(__VA_ARGS__) #else # define DLog(...) /* */ #endif #define ALog(...) NSLog(__VA_ARGS__)

Disliking more and more sqlite3_exec with callback

iphonelite3 — Tue, 03 Feb 2009 14:38:06 +0000

The callback approach in sqlite3_exec is really complicating my code. I used it initially for select: and then re-used for count: with where clause. The problem is that you have to pass the context to the C function and back and you need flexibility in handling the result set. I will cleanup the code and move to the more verbose sqlite3_prepare_v2 and friends.

With the modification above I will be able to add a small cache of compiled statements, will have to run some memory/performance numbers on it to tune it for my usage.

Deserializing json

iphonelite3 — Mon, 02 Feb 2009 07:04:14 +0000

When you rely on the default json deserialization in Rails the json for each object starts with its own root. For example
[ {"user": {"id":1, "name":"Jon Dhoe"}, {"user":{}}]
The code in iphonelite3 tries to take care of this when processing the NSDictionary resulting from the json parsing.

You can actually change the behavior of Rails in file new_rails_defaults.rb, change the true to false in the following line.
ActiveRecord::Base.include_root_in_json = true

GTM Unit tests and memory allocation

iphonelite3 — Fri, 30 Jan 2009 23:31:47 +0000

While everybody says that memory allocation is trivial in Cocoa it took me a while to be confident with it. You can read the docs all you want, memory allocation bugs are hard to track down and it is hard to get the proper confidence. Part of my challenge is that it is not always clear which functions of the framework (or even yours) are doing an autoRelease() or not. I guess you need to spend here 10% of the 10000 hours required to become effective in Cocoa programming

Enter the iPhone Unit Test in the Google Toolbox for Mac: http://code.google.com/p/google-toolbox-for-mac/.
An autorelease pool is setup before each test and then released. This allows you to play with retain and release, make the program crash by releasing twice or releasing an autoreleased pointer. I found out that being able to predictably crash the unit tests significantly increased my confidence with the memory management functions.

The GTM Unit Tests are integrated in the iphonelite3 on github. Feel free to use as a starting point for your own projects.

Unit tests crash

iphonelite3 — Fri, 30 Jan 2009 21:51:48 +0000

As in real life the following piece of code will crash your unit test and the error message will be totally useless.
-(void) init { }

The following will work
-(id) init { [super init]; return self; }

Better start small, test often and pay attention.

Code assumptions

iphonelite3 — Fri, 30 Jan 2009 16:10:03 +0000

The serializable classes do not have to define from a base class, this is more similar to Hibernate thant ActiveRecord in that aspect.

Right now the table and class name are arbitrary but I am thinking about following the ActiveRecord convention (lowercase class name and add an ‘s’).

Each class has an int id field (synthetic id). This is mapped to a int _id inside Objective-C (since id is a reserved word).

For each database field that is to be serialized you define a property, the names have to match.

To symbolize a ManyToMany relationship you define a C array of objects of the other side.


@interface User
@end
@interface Group
User** users;
@end

The name of the link table uses the ActiveRecord convention: first table name _ second table name.