Cocoa Touch UIViewController Properties and class design

Question

I'm creating a custom ViewController. This VC needs to load some data that is known in the event that creates it and pushes it to the top of the NavigationController that it is going to be part of.

My question is, how should I pass data from the view that handles the custom ViewController's creation into that custom ViewController.

I've thought of four possible options, and I was hoping to get feedback on why each one is good or not for this functionality.

1) Expose public properties in the custom ViewController and set the UI elements in the view based on those properties in - (void) ViewDidLoad.

2) Expose the actual UI elements themselves and set their .text/.image/.whatever attributes as the ViewController is being created.

3) Create a custom constructor for the custom view and pass in the values I need to set up the UI elements

4) Create a custom model that both views have access to, set the data before the CustomView is created/pushed, and access that data in the ViewDidLoad event.

I'm still new to all of this, and I want to make sure that I understand the proper handling of these handoffs of data. It seems like something like this is probably a simple answer, but I'm still a little confused and its probably really important to do this right to avoid memory loss/leaks.

Also, in case anyone cares, I'm using Stanford's CS193p class on iTunes U and Mark/Lamarche's "Beginning iPhone Development" to teach myself cocoa for the iPhone. I'm working on an application with a NavigationController and a couple ViewControllers (Presence 1 if you're familiar with 193p).

Answer 1

Well, I believe there are advantages & disadvantages to each of those methods depending on your requirements...often it will require some combination of approaches. I believe the most common, for me anyway, is to do something like this where you give it enough to get started.

MyViewController *vc = [[MyViewController alloc] init]; // (or initWithNibName:bundle:)
// transfer vc values here
vc.value1 = aValue;
vc.value2 = anotherValue;
[self.navigationController pushViewController:vc animated:YES];
[vc release];

After your view controller is instantiated you have an opportunity to pass objects to it. Say MyViewController is a detail view then you'd give it the object it will be displaying the details for. Or, if it's a table view you can give it the NSArray it will need for display. Then in viewDidLoad or awakeFromNib or awakeFromCoder, or... you can fill out the view...so to speak.

Answer 2

#1 is fine, with or without #3 (these two are not mutually exclusive)

#4 is my preferred solution. For instance, if I had a UserViewController, I would probably also like to have a User object and create it this way:

User *user = [self.users objectAtIndex:someIndex];
UserViewController *uvc = [[[UserViewController alloc] initWithUser:user] autorelease];

#2 is not a good idea. Objects should not access the UI elements of other objects. Much trouble comes from this when you decide to change your UI around (and you will).