Difficulty accessing property on another class

Question

I feel I must be going about this the wrong way and there is probably a very simple solution that I cant seem to find. In ClassA.h I have:

@property (strong, retain) NSManagedObject *form;

In ClassB I have tried:

#import "ClassA"

@interface ClassB  ()
{
    ClassA *classA;
}

Then in viewDidLoad I have:

NSLog(@"form::%@", classA.form);

but its nil everytime even though when Im on classA (its a viewcontroller) it definitely has a value.

EDIT:

So I followed the example given by BlackRider classA

 MyManager *sharedManager = [MyManager sharedManager];
    sharedManager.someProperty = self.form;

classB

MyManager *sharedManager = [MyManager sharedManager];

                    NSLog(@"globalform::%@", sharedManager.someProperty);

and Im still getting null value in the log print.

Show us the code that initializes `classA` to some existing instance of `ClassA`. — rob mayoff, Nov 13 '13 at 21:23
@robmayoff Im sorry but what do you mean the code that initializes classA. Its a viewcontroller for a storyboard view — BluGeni, Nov 13 '13 at 21:29
You need to actually set your `ClassA` variable in your `ClassB` view controller to something. If you are using storyboards the easiest way to set things between view controllers is in `prepareForSegue`. — ThisDarkTao, Nov 13 '13 at 21:32
`ClassA *classAInstance = [[ClassA alloc] init];` then you can `NSLog(@"form::%@", classAInstance.form);` I would possibly recommend looking at singletons in objective-c — Popeye, Nov 13 '13 at 21:41
@Popeye I have never used a singleton before but Im not against it. How would it look? — BluGeni, Nov 13 '13 at 21:51
A good example of one is here http://stackoverflow.com/questions/145154/what-should-my-objective-c-singleton-look-like answered by `Ben Hoffstein` — Popeye, Nov 13 '13 at 22:03

score 1 · Answer 1 · answered Nov 13 '13 at 21:46

You really should make ClassA a property of ClassB using @property (nonatomic, strong) ClassA *classA; in the interface, this will generate a setter and getter for you. Using a plain C variable like you have done means you can only access it using -> pointer indirection, and it will be protected by default. Mostly people use these kinds of variables in a class extension in their implementation, but properties on their interface.

Wherever you instantiate your ClassB class, set its classA property using classB.classA = self;

For example:

- (void)loadMyForm {
    ClassB *classB = [ClassB alloc] init];
    classB.classA = self;
}

score 0 · Answer 2 · answered Nov 13 '13 at 21:33

0

Since you use a storyboard (and probably segues) here's what you can do:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // Get a reference to the destination view controller
    if([[segue destinationViewController] isKindOfClass:[ClassA class]]) {
        ClassA *vc = [segue destinationViewController];

        // now you can access vc.form
    }
}

answered Nov 13 '13 at 21:33

TotoroTotoro

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ClassA is a view controller for a storyboard but ClassB is not. – BluGeni Nov 13 '13 at 21:41
In this case it gets a little more clunky. Cause it's in the method above that you can first access the view controller instance. Like someone else suggested in a comment, consider making the `form` object a singleton. – TotoroTotoro Nov 13 '13 at 21:50
How would a singleton look for me? – BluGeni Nov 13 '13 at 21:51
I followed this code example but am still getting a null value in classB Refer to my updated question for the code I used – BluGeni Nov 13 '13 at 22:15
2

Do not learn about singletons until you figure out how basic properties work. You will end up with tons of pointless singletons. – Aaron Brager Nov 13 '13 at 22:19
I agree with @AaronBrager. – TotoroTotoro Nov 13 '13 at 22:21

score 0 · Accepted Answer · answered Nov 18 '13 at 16:45

0

I ended up using my appDelegate and using it to store a "global" variable.

answered Nov 18 '13 at 16:45

BluGeni

3,378
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Difficulty accessing property on another class

3 Answers3

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