Delegation and dismissal of a view controller - iphone

Question

I'm doing an app that has a UITableViewController populated with a list of products. Each row segues to a UIViewController that presents the details of the product in the row. Now since tapping on each row and going back to see the details of the next product might be too tedious for the user, we decide to add this feature: when a user swipes on the UIViewController of a product, then the UIViewController with the details for the next product is pushed.
But, as of now, I'm not sure of the best way to implement this. I'm tempted to pass the array of products to the UIViewController so that the swiping is achieved but this will be a violation of the MVC framework,right? Views cannot own the data they're presenting. The product details UIViewController should only know about the specific product that's passed to it, not the rest, right?
I think this can be accomplished using delegation but I'm not sure how. Can anybody help me? Thanks!
EDIT:
Rob Mayoff's code was really helpful so I decided to implement it. But for the meantime, instead of implementing a swipe, I'll just use a simple round rect button to call the functions.
- (IBAction)showNextProduct:(id)sender {
[self.productsTVC goToProductAtIndex:self.productIndex + 1];
}
- (IBAction)showPriorProduct:(id)sender {
[self.productsTVC goToProductAtIndex:self.productIndex - 1];
}
But every time I click any of the buttons, my app crashes with the message: Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree might get corrupted. Unbalanced calls to begin/end appearance transitions for <ProductDetailsViewController: 0x6e510c0>.

Answer 1

Let's say you have a CatalogViewController (which is a subclass of UITableViewController) and a ProductViewController (which is a subclass of UIViewController).
The simplest way to implement “swipe to next product” is to give the ProductViewController a reference to the CatalogViewController. It should be weak (if using ARC) or assign (if not using ARC). You will also want a property that holds the index of the product in the catalog:
#interface ProductViewController
#property (nonatomic, weak) CatalogViewController *catalogViewController;
#property (nonatomic) NSInteger productIndex;
#end
Then in the action method for a swipe, you send a message to the CatalogViewController asking it to go to the next (or prior) product in the catalog:
#implementation ProductViewController
- (IBAction)showNextProduct:(id)sender {
[self.catalogViewController goToProductAtIndex:self.productIndex + 1];
}
- (IBAction)showPriorProduct:(id)sender {
[self.catalogViewController goToProductAtIndex:self.productIndex - 1];
}
In CatalogViewController, whenever you create a ProductViewController, you need to set those properties:
#implementation CatalogViewController
- (ProductViewController *)productViewControllerForProductAtIndex:(NSInteger)index {
if (index < 0 || index >= self.products.count)
return nil;
ProductViewController *vc = [[ProductViewController alloc] initWithProduct:[self.products objectAtIndex:index]];
vc.catalogViewController = self;
vc.productIndex = index;
return vc;
}
and you implement the goToProductAtIndex: method like this:
- (void)goToProductAtIndex:(NSInteger)index {
ProductViewController *vc = [self productViewControllerForProductAtIndex:index];
if (!vc)
return;
NSMutableArray *vcs = [[self.navigationController viewControllers] mutableCopy];
while (vcs.lastObject != self)
[vcs removeLastObject];
[vcs addObject:vc];
[self.navigationController setViewControllers:vcs animated:YES];
}
You can use the same method to handle a table row selection:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[self goToProductAtIndex:indexPath.row];
}
If you want to get more software-engineery, you can create a protocol around the goToProductAtIndex: method and use that to avoid making ProductViewController know about the CatalogViewController class.