Question

I tried to find a solution here but was unable to, basically I have an interactive subview that I need to switch to a new interactive subview from within the subview. I am able to change subviews easily with an IBAction in the main view, but I have been unsuccessful changing the view from within the subview. Here’s the code… which should make what I am trying to accomplish more clear.

in .h of MainViewController

@interface MainViewController : UIViewController {
    IBOutlet OneViewController *oneviewController;
    IBOutlet TwoViewController *twoViewController;
}

-(IBAction)goToView;

@property (nonatomic, retain) IBOutlet OneViewController *oneviewController;
@property (nonatomic, retain) IBOutlet TwoViewController *twoViewController;

@end

in .m

@implementation MainViewController

@synthesize oneviewController;
@synthesize twoViewController;

-(IBAction)goToView {   
    [self.view addSubview:twoViewController.view];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    [self.view addSubview:oneviewController.view];  
}

Ok this all works great, i am able to load both ViewControllers with xib and all their` buttons work etc. ..
But when I try…

in .m of OneViewController

#import "MainViewController"

...
[MainViewController.view addSubview:twoViewController.view];  ...

this does not work, I have tried a variety of things, by adding the twoViewController to the .h of oneViewController, but it crashed… I am still very new to all this so It is likely I am missing the obvious. Thanks for help!!

I also tried this in the .m of OneViewController

but it still crashed… although the build succeeded

MainViewController* mySuperView = (MainViewController*)self.view.superview;
TwoViewController *twoViewController;
[mySuperView.view addSubview:twoViewController.view];

Answer 1

This action is being done in the wrong place. If you are trying to add a subview to your MainViewController, you should really handle that inside of MainViewController.m. You are calling:

[MainViewController.view addSubview:twoViewController.view];

but MainViewController.view is a static instance of view. If you want to keep it as is, and assuming OneViewController is already a subview on MainViewController, you should do something like this:

UIView *main = [OneViewController.view superview];
[main addSubview:twoViewController.view];

This is pretty dangerous though because you’re not guaranteed to have a superview for this view. I’d just handle all of this inside MainViewController. No controller should have the power to add a subview to another controller unless it had an instance of MainViewController.