Objective-c: How to invoke method in container view controller [duplicate]

Answer 1

You should be able to access the viewcontroller's child through parent's childViewControllers property. (Or using the segue as pointed out above).

Eg:

BlueViewController *bvc = self.childViewControllers[0]; //assuming you have only one child 
[bvc someMethod];

Answer 2

I usually grab the controller object in the prepareForSegue method.

Here is some code I use. Remember that my naming convention for segues is always class name + Segue, so the segue for ActionMenuVC is ActionMenuVCSegue. This way is save to grab the right view controller.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([[segue identifier] isEqualToString:[self.appDelegate segueIdentifierForClass:[ActionMenuVC class]]]) {
        self.actionMenuVC = [segue destinationViewController];
        self.actionMenuVC.delegate = self;
    }
    else if ([[segue identifier] isEqualToString:[self.appDelegate segueIdentifierForClass:[ResizeableImageVC class]]]) {
        self.resizeableImageVC = [segue destinationViewController];
        self.resizeableImageVC.delegate = self;
        self.resizeableImageVC.visible  = NO;
   }
}