Properties are null outside of viewDidLoad - objective-c

Question

Two properties:
#property (retain, nonatomic) NSString *drinkType;
#property (retain, nonatomic) NSString *wheelType;
When accessed from viewDidLoad as self.drinkType, etc, they hold the value I expect. However, when accessed from a public method
-(void)updateSentenceWithSelectedAromas:(NSMutableArray *)selectedAromas;
they are null. What is happening here?
The "selectedAromas" array is passed from another controller to this method.
ViewController *aromaVC = [[ViewController alloc] init];
[aromaVC updateSentenceWithSelectedAromas:selectedAromas];
ViewController.h
-(void)updateSentenceWithSelectedAromas:(NSMutableArray *)selectedAromas;
#property (retain, nonatomic) NSString *drinkType;
#property (retain, nonatomic) NSString *wheelType;
ViewController.m
- (void)viewDidLoad
{
[super viewDidLoad];
// This is working
NSLog(#"The drink type is:%#", self.drinkType);
}
-(void)updateSentenceWithSelectedAromas:(NSMutableArray *)selectedAromas {
// This returns null
NSLog(#"The drink type is:%#", self.drinkType);
}

Answer 1

I think your missing quite a few things, which leads me to think that you're missing some basic understanding of variable scope in ObjectiveC, let's see if this helps you in some way:
First, your selectedAromas array has no relation whatsoever with drinkType and wheelType. So passing this array to the ViewController seems irrelevant.
Second, in your ViewController you're declaring your own drinkType and wheelType variables, so there's no way they will have the value of some other class or Controller.

Answer 2

You probably aren't setting your properties soon enough (init would be a good place). viewDidLoad is called much later in relation to the code you posted.

Answer 3

Okay, Michael Dautermann was absolutely right. The method updateSentenceWithSelectedAromas was in fact running in a separate instance of the view controller. To solve this problem I implemented a protocol listener with my method and set the delegate of the child controller to its parent using a segue.
Thank you everyone for all your help.
In case anyone stumbles upon this, here is what I did:
ViewController2.h
#protocol updateSentenceProtocol <NSObject>
//Send Data Back To ViewController
-(void)updateSentenceWithSelectedAromas:(NSMutableArray *)selectedAromas;
#end
#interface ViewController2 : UIViewController
// delegate so we can pass data to previous controller
#property(nonatomic,assign)id delegate;
#end
ViewController2.m
#synthesize delegate;
-(void)someMethod {
[delegate updateSentenceWithSelectedAromas:selectedAromas];
}
ViewController.m
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"viewController2Segue"])
{
// Get reference to the destination view controller
ViewController2 *vc = [segue destinationViewController];
vc.delegate = self;
}
}
-(void)updateSentenceWithSelectedAromas:(NSMutableArray *)selectedAromas {
// do stuff with array and properties as needed
}