Method not working when called from another class - ios

Question

I am trying to call the method addObjectToArray from SecondViewController.m. The NSLog works, however I cannot add "foo" to _myArray (an NSMutableArray that is the data source for the UITableView). If I call [self addObjectToArray] in viewDidLoad, then it works fine.
FirstViewController.m
-(void)addObjectToArray {
[_myArray addObject:#"foo"];
[_myTableView reloadData];
NSLog(#"it works");
}
SecondViewController.m
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"identifier"]) {
FirstViewController *controller = [segue destinationViewController];
[controller addObjectToArray];
}
}

Answer 1

As per Nofel Mahmood's comment, you are creating two separate instances of FirstViewController, one named firstViewController (created from the storyboard) and one called myObject (created with the 'new' method). You then call the addObjectToArray method on myObject, but you present firstViewController. Your myObject is essentially redundant. Amend your code as follows:
-(IBAction) doSomething:(id)sender {
FirstViewController *firstViewController = [self.storyboard instantiateViewControllerWithIdentifier:#"firstViewController"];
[firstViewController addObjectToArray];
[self presentViewController:firstViewController animated:YES completion:nil];
}
EDIT
Since you want to return to an existing instance of FirstViewController, you need to use an unwind segue. There's a detailed explanation here: what-are-unwind-segues, but in your case:
In FirstViewController, add a new method:
- (IBAction)unwindToFirst:(UIStoryboardSegue *)unwindSegue {
[self addObjectToArray];
}
Then in your storyboard, ctrl-drag from the SecondViewController (or if you prefer, from a specific control in the view) to the green "Exit" icon in the bar below the SecondViewController. You should then select the unwindToFirst action in the small popup that appears.
If you want to use this unwind segue from code, look in the Document Outline on the left hand side of your storyboard for the Unwind Segue you just created. Select this, and then add an identifier in the attributes inspector on the right hand side. You can then call this segue from code using the normal [self performSequeWithIdentifier:...] method.