ipad objective c using removeFromSuperview to remove UICollectionViewController throws an error - objective-c

Question

So I'm customizing this control I found since I think it works very well except with this issue of mine:
http://www.cocoacontrols.com/controls/fsverticaltabbarcontroller
I wanted to load a UICOllectionViewCOntroller instead of a regular ViewController whenever an item is tapped on the sidebar. So I did this modification when selecting an item:
- (void)setSelectedIndex:(NSUInteger)selectedIndex
{
NSLog(#"selected Index is %#", [NSNumber numberWithInt:selectedIndex]);
NSLog(#"_selected Index is %#", [NSNumber numberWithInt:_selectedIndex]);
NSLog(#"vc counts is %i", [self.viewControllers count]);
if (selectedIndex != _selectedIndex && selectedIndex < [self.viewControllers count])
{
// add new view controller to hierarchy
UIViewController *selectedViewController = [self getSelectedVCWithSelectedIndex:selectedIndex];
[self addChildViewController:selectedViewController];
selectedViewController.view.frame = CGRectMake(self.tabBarWidth,
0,
self.view.bounds.size.width-self.tabBarWidth,
self.view.bounds.size.height);
selectedViewController.view.autoresizingMask = UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth;
[self.view addSubview:selectedViewController.view];
// remove previously selected view controller (if any)
if (_selectedIndex != NSNotFound)
{
UIViewController *previousViewController = [self.viewControllers objectAtIndex:_selectedIndex];
NSLog(#"ERROR HERE: remove previous: previousVC = %#", previousViewController);
[previousViewController.view removeFromSuperview];
[previousViewController removeFromParentViewController];
}
// set new selected index
_selectedIndex = selectedIndex;
// update tab bar
if (selectedIndex < [self.tabBar.items count])
{
self.tabBar.selectedItem = [self.tabBar.items objectAtIndex:selectedIndex];
}
// inform delegate
if ([self.delegate respondsToSelector:#selector(tabBarController:didSelectViewController:)])
{
[self.delegate tabBarController:self didSelectViewController:selectedViewController];
}
}
}
So what I did is since it already handles the index number of the items on teh sidebar, I just made sure it instantiates the type of controller it needs to load using this line, I have 3 regular VC and 1 collection VC:
UIViewController *previousViewController = [self.viewControllers objectAtIndex:_selectedIndex];
This is how it looks like:
-(UIViewController *)getSelectedVCWithSelectedIndex:(NSUInteger)selectedIndex{
UIViewController *selectedVC = [[UIViewController alloc]init];
// do a switch case on this.
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:#"MainStoryboard" bundle:nil];
// need to instantiate each and every custom uinav
switch(selectedIndex){
case 1:
selectedVC = [storyboard instantiateViewControllerWithIdentifier:#"UINavAdminCategoryIndexViewControllerID"];
break;
case 2:
selectedVC = [storyboard instantiateViewControllerWithIdentifier:#"UINavAdminParticipantIndexViewControllerID"];
break;
case 3:
selectedVC = [storyboard instantiateViewControllerWithIdentifier:#"UINavAdminTablesIndexCollectionViewControllerID"];
break;
case 4:
selectedVC = [self.viewControllers objectAtIndex:selectedIndex];
break;
default:
break;
}
return selectedVC;
}
Now everything would load smoothly, but whenever I would go to the Collection VC tab and then move away from it by going to another tab it would throw this error:
* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'UICollectionView must be
initialized with a non-nil layout parameter'
The application bombs on this part when I remove it from the superview:
[previousViewController.view removeFromSuperview];
Was wondering why it would instantiate the UIView again when all I'm doing is removing it from the stack (is that the right term?)
EDIT: Added some more codes

Answer 1

So I finally figured it out and hopefully someone else can find this useful. When generating a UiCollectionView you need to initiate the Layout for some reason. Idk why, I will try to find out. But this is what led me to the solution:
http://www.rqna.net/qna/ikvmhu-uicollectionview-must-be-initialized-with-a-non-nil-layout-parameter.html
Before when I instantiated the CollectionViewController on the main ViewController before the FSVerticalTabbar is called I just used the class connected to the ViewController on the storyboard eg. AdminMainController, AdminEventsCollectionController, etc.
I basically just added the Layout and used that for the UICollectionViewController when being initiated. It now removes the VC without any errors.
UICollectionViewFlowLayout *aFlowLayout = [[UICollectionViewFlowLayout alloc] init];
[aFlowLayout setItemSize:CGSizeMake(200, 140)];
[aFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
myCollectionViewController = [[MyCollectionViewController alloc]initWithCollectionViewLayout:flowLayout];