View Full Version : Properties

May 16, 2011, 01:05 PM

I started learning Objective-C a few weeks ago. By doing a lot of tutorials I already understood the main purpose of properties in Objective-C, but there are a few things, which are not quiet clear yet.
First question would be when it's better to only use a property instead of using a property + an instance variable, which are named the same.
Secondly, why would you name instance variable + property differently and then assign them in the @synthesize - part,
e.g: @synthesize window = _window


May 16, 2011, 01:30 PM
On the iPhone runtime you don't have the option of a declared property and no variable. So don't worry about that. Basically the option of not having the variable was added to the, so-called, "modern" runtime.

As for why you'd use a variable with a different name? Basically to prevent you assigning values directly to the variable as if you do this the setter does not get called and any side effects (like retain) don't get called.

May 16, 2011, 02:13 PM
Thanks for the quick reply.
Regarding my second question...is the default behaviour that the setter is called when variable and property have the same names?
And how about IBOutlets / IBActions as properties...I've seen code where an instance variable was used, in another tutorial it wasn't. Are there any specific situations where using both should be preferred and where not?

May 16, 2011, 02:48 PM
This calls the setter

myObject.property = value;

From an instance method this calls the setter

self.property = value;

This does not call the setter (ever)

property = value;

I would suggest always ensuring the setter gets called.

May 16, 2011, 03:28 PM

And what about the IB-thing...when should I use property only and when not?