Question

I was wondering how I would go about accessing one instance of a class, say “ship class” across multiple views.

Lets say I have a rootViewController and three subviews, one Main, one battle, and one landing. Where exactly would I implement an instance of a class that stores all the information on my ship and access it though the other views. If my ship has x missiles left, how does another view access that information to display it. If I implement it on the Main view how does the landing view get that info?

I know there has to be an easy way to do this, and I bet there is a way you are supposed to do it without implementing the ship class in any of the views per se. I am still fairly new to programming for the iPhone though.

Thank you in advance for any help you all may provide.

Answer 1

Once you have created the single instance of your Ship class, you need to tell any other views what that instance is. So you could make Ship a public property on the class that created it.

@property (nonatomic, retain) Ship* myShip;

Suppose that class is the app delegate – then, in another file, you’d write something like

[[[UIApplication sharedApplication] delegate].myShip getNumberOfMasts];

This is simple, and works for a simple project, but it does make the Ship object available to any file in your project – it effectively becomes global data, which can be hard to debug in a larger project. (If something bad is happening to myShip, which object was responsible? If it could be any object in your app, then this is a harder problem to debug than if access is restricted to the two classes that need it.) So, if you want to restrict access to ship, then don’t make myShip a public property – instead have the object that created myShip pass it in initialisation calls when it creates other objects that need access. Something like this

[[myBattleController alloc] initWithShip:myShip];

If this really is one and only one ship object for the whole application, search on stack overflow for advice on creating singleton objects.