Question

I’m following Stanford cs193p lesson 7 about using SplitViewControllers and protocols.
I’m doing the same exact stuff the professor is doing (checked multiple times) but I get this error over and over.

I defined a protocol in SplitViewBarButtonItemPresenter.h

#import <UIKit/UIKit.h>

@protocol SplitViewBarButtonItemPresenter <NSObject>
@property (nonatomic,strong) UIBarButtonItem *splitViewBarButtonItem;
@end

in my master CalculatorViewController.h

@interface CalculatorViewController : UIViewController <UISplitViewControllerDelegate>

in CalculatorViewController.m

-(id <UISplitViewControllerDelegate>)splitViewBarButtonItemPresenter
{
    id detailVC = [self.splitViewController.viewControllers lastObject];
    if(![detailVC conformsToProtocol:@protocol(SplitViewBarButtonItemPresenter)]){
        detailVC = nil;
    }
    return detailVC;
}

- (void)awakeFromNib
{ 
    [super awakeFromNib];
    super.splitViewController.delegate = self;
}

and later when I try to set the barButtonItem

-(void)splitViewController:(UISplitViewController *)svc
    willHideViewController:(UIViewController *)aViewController
         withBarButtonItem:(UIBarButtonItem *)barButtonItem
      forPopoverController:(UIPopoverController *)pc
{
    barButtonItem.title = self.title;
    [self splitViewBarButtonItemPresenter].splitViewBarButtonItem = barButtonItem;
}

I keep getting the error in the title as if I didn’t properly declare the protocol and the delegate. I really don’t know where else to look for errors since I’m following what the Stanford’s professor does line by line, letter by letter.
The error is in this line, specifically:

[self splitViewBarButtonItemPresenter].splitViewBarButtonItem = barButtonItem;

Answer 1

First of all, you have an infinite recursion in your code:

-(id <UISplitViewControllerDelegate>)splitViewBarButtonItemPresenter
{
    id detailVC = [self.splitViewController.viewControllers lastObject];
    if(![detailVC conformsToProtocol:@protocol(SplitViewBarButtonItemPresenter)]){
        detailVC = nil;
    }
    return [self splitViewBarButtonItemPresenter] ? UIInterfaceOrientationIsPortrait(UIInterfaceOrientation) : NO;
}

The method calls itself in the return statement and there’s no abort condition.
Second, even if that method would return a value, it would return a BOOL but it’s supposed to return an id<UISplitViewControllerDelegate>.

Third, either the return type of the method is wrong or the name is misleading. You have a protocol called SplitViewBarButtonItemPresenter and the name of the method is splitViewBarButtonItemPresenter. So from the name I would expect it to return an id<SplitViewBarButtonItemPresenter> not an id<UISplitViewControllerDelegate>.

Last but not least, your SplitViewBarButtonItemPresenter protocol is not implemented by the CalculatorViewController.

So there are a lot of problems with your code and I would suggest to check that even more often.