How do I copy objects into ivars for later use?

Question

Objective c | xcode | iphone question

Im building a model(data) class for a monetary transaction and have kind of a basic/noob question regarding pointers and object copying. The Transaction class I'm creating contains 4 or 5 ivars/properties that represent object type variables. now when I get the user entered data from the view controller to populate these ivars is it safe to use pointers or do i need to make a copy of the object and then assign that to the ivar?

Because I'll need to store these transactions after the user exits the program I'm assuming that any references I made to pointers in a previous session will be essentially broken links. Am i wrong here, any explanation and maybe some code examples would be appreciated.

If you have any suggestions as far as how to store the data while the app is not in use that would also be helpful.

Thanks so much,

Nick

Answer 1

I would suggest re-reading the intro guides as you seem to be a bit off the rails here; over-thinking the basics. No big deal, we've all been there (still are there when faced with new stuff, often!).

First, for any string value, copy it. In terms of properties, which you should use, you would want:

@property(copy) NSString *myString;

Make sure you -release myString in your -dealloc method.

For other kinds of values, it is really context dependent. Copying is often the safe route. NSDate and NSNumber instances happen to be immutable so copies are irrelevant, but free.

As far as saving data, you are semi-correct. Pointers do not remain valid/same across running sessions with your application. If you need to save data, you explicitly do so through any of a number of common mechanisms. For dead-simple data in an entirely non-document based, app specific, role, user defaults might be enough. Otherwise, see the documentation regarding archiving data.