CODEWITHSUNDEEP
iosobjective-cclassproperties
Jordan H
Jordan H

Reputation: 55675

Objects in class are nil when trying to access from another class

I have a View Controller class which contains a button property, and I need to change its enabled stated from a different class (Table View Controller). I'm also calling a method that's in that VC class. I can call the method just fine, but when I try to access the button property, it's nil. Actually all of its properties are nil. I must have something not set up quite right.

//ViewController.h
@property (strong, nonatomic) IBOutlet UIButton *aButton;
- (IBAction)myButtonTapped;

//ViewController.m
//did not override setter or getter for aButton
- (IBAction)myButtonTapped {
     //code here
}

//Table VC.m
@property (strong, nonatomic) ViewController *myVC;

- (ViewController *)myVC {
    if (!_myVC) _myVC = [[ViewController alloc] init];
    return _myVC;
}

- (void)userEnteredText:(NSNotification *)notification {
     [self.myVC myButtonTapped]; //runs method without issue
     self.myVC.aButton.enabled = YES; //does not occur since aButton is nil - myVC is not nil
}

Upvotes: 0

Views: 440

Answers (1)

Paulw11
Paulw11

Reputation: 114773

You need to study the information provided by @Hot Licks to understand how to keep references between your objects, but I can tell you that part of your problem is your getter method -

- (ViewController *)myVC {
    if (!_myVC) _myVC = [[ViewController alloc] init];   //  <-- This is a problem
    return _myVC;
}

If your _myVC variable is nil then your getter method allocates a new ViewController - so you won't get a reference to the existing viewController. As you then call the plain init method for your new viewController none of its properties will be initialised - so you get nil for your button.

You don't need to write any code for a simple property like this - the default code that is created for you is all you need. What you do need to do is set the myVC property from your current viewController instance. So somewhere in your viewController you will have

tableVC.myVC=self;

You will need to do this somewhere where you have a reference to your tableVC - so this could be inprepareForSegue if you are using storyboards and segues or wherever you present or push the table vc if you aren't

Upvotes: 1

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