Properties in Objective-C can be quite useful sometimes, but you have to be careful because they don’t always work how you think they should. Here is a common gotcha among people new to Obj-C and properties.

Consider we have a class called Sprite, which has a property called position.

@interface Sprite : NSObject {
  CGPoint position;
}

@property (readwrite) CGPoint position;

@end

CGPoint is a struct with 2 int variables, x and y.

Lets create one:

Sprite mySprite* = [[Sprite alloc] init];

Now consider the situation of getting and setting the position.

Getting
When you call this:

CGPoint pos = mySprite.position;

It is actually the same as:

CGPoint pos = [mySprite position];

Here its clear that pos is a copy of the position (its not a reference
to the instance variable).

Setting
When you can call:

mySprite.position = pos;

It is actually the same as:

[mySprite setPosition:pos];

OK this is probably fairly clear so far!

The Gotcha
Now this is where the issue happens.

When you call this:

mySprite.position.y = 99;

It is actually the same as this:

[mySprite position].y = 99;

In this instance, the position variable of mySprite is not changed at all.

So when using properties, try to be aware of what Objective-C is actually doing behind the scenes :)

Posted: November 1st, 2008 under Mac, Objective C, iPhone.
Comments: none

Was having trouble figuring out how to deactivate the itunes account on the iPhone.

I finally figured it out though:

1. Plug in your iPhone into your computer.
2. Open up iTunes.
3. Sign out of iTunes account on your computer (on Mac, this is under the Store menu).

Posted: October 24th, 2008 under Mac, iPhone.
Comments: none

I asked myself a question: “Hmm, I wonder if its possible to sync my N95 with my mac”. My answer: “Doubt it”…

Funny that, I am now not only able to sync my N95 with my Mac, I also don’t need todo anything because it does it all automatically when I move my N95 within bluetooth range of my Mac. I love my Mac :)

For those wondering how I did it, I followed this useful guide that pretty much walked me through it. To summarise what you need from that post:

1. iSync

   This was already on my Macbook with Leopard.

2. Nokia N95 plugin for iSync

   This was probably the only step that caused me problems. The latest version of iSync is 3.0, and Nokia’s iSync plugins are only for 2.4. So in the end, I had to purchase a plugin from here. It was only 8 pounds though, so for me it was well worth it.

3. Home Zone

   This is what detects when your device gets in Bluetooth range and starts a script. You can get it from here.

4. Automator app for the sync

   You can get this from here. You just need to unzip it, and put it in your Applications folder (or somewhere you can find it).

I recommend following through the guide though, its pretty straight forward :)

Posted: April 10th, 2008 under Mac.
Comments: none