Back button not removing from the stack?

Question

Hi,
I have the following code:
[[self navigationController]pushViewController:_newsDetailController animated:YES];
However, It doesn't seem to be removing from the stack when the user hits the back button on the UINavigationBar.
The reason I believe this, is because when you then select another item in my UITableView, it loads exactly the same details as the first time.
I have tried [_newsDetailController release]; but it still doesn't make any difference. It just crashes after the third selection.
This is what I'm doing in my didSelectRowAtIndexPath:
- (void)tableViewUITableView *)tableView didSelectRowAtIndexPathNSIndexPath *)indexPath {
[[self appDelegate] setCurrentlySelectedBlogItem:[[[self rssParser]rssItems]objectAtIndex:indexPath.row]];
[self.appDelegate loadNewsDetails];
Any help would be greatly appreciated. I've spent ages on this!
It worked fine until I added a UINavigationController.
Thanks,
Nick

Answer 1

Hi Nick, and welcome to the Dev Forum,
nrawlins wrote:
... It doesn't seem to be removing from the stack when the user hits the back button on the UINavigationBar.
I understand how your observations could make it seem like your _newsDetailController is somehow staying on the stack, but that's not what's going on here. If you want to see the stack, just add some logging before and after pushing or popping:
NSLog(@"stack: %@", self.navigationController.viewControllers);
I think we'll need to see more of your code to isolate the problem, but what we're looking for is a logic mistake which causes the detail controller to always display the info for the same item, regardless of which item is selected next. Here's a list of questions to guide your search, and/or show you which code we need to look at:
1) What's in the array returned by [[self rssParser]rssItems] ? It might help to add some logging in tableView:didSelectRowAtIndexPath like this:
- (void)tableView(UITableView *)tableView didSelectRowAtIndexPath(NSIndexPath *)indexPath {
NSArray *item = [[[self rssParser]rssItems]objectAtIndex:indexPath.row]];
NSLog(@"%s: item=%@", _func_, item);
[[self appDelegate] setCurrentlySelectedBlogItem:item];
[[self appDelegate] loadNewsDetails];
2) What does loadNewsDetails do? It looks like it finds the details for the item stored in currentlySelectedBlogItem. Is that right? Some logging in loadNewsDetails might help to make sure the correct details are loaded there. From your description it sounds like you already had this part of the code working right, but it wouldn't hurt to be sure it's still doing what you expect;
3) How does the data obtained in loadNewsDetails find its way to the details controller? This is the missing link not shown in the code you've posted so far. I think we need to look at:
3.1) Where and when the details controller is created;
3.2) Whether the same controller object is intended to persist from item to item, or whether a new instance of the controller is created each time an item is selected. The latter scheme is usually preferred for best memory management;
3.3) Is the current item and detail data stored in the detailsController or the app delegate? When is it stored, and when is it used?
For example, suppose the details controller is only created once and persists for the life of the table view. Then suppose loadNewDetails saves the new details in an ivar of the app delegate, and the code to fetch the new details is in viewDidLoad of the controller.
In the above scenario, viewDidLoad would run after the details controller was created, and if the details of the first selection were loaded by then, the details for the currently selected item would
be presented as expected. But viewDidLoad will normally only run once, so when the selection was changed, the new details would never be fetched, and the previous details will be displayed again.
The best way to avoid this and other related scenarios, is to create a new details controller each time a new selection is made from the table view:
// MyTableViewController.m
#import "myAppDelegate.h"
#import "NewsDetailController.h"
// called by loadNewsDetails as soon as details have been loaded
- (void)presentDetailController {
NewsDetailController *viewController = [[NewsDetailController alloc] // vc retainCount is 1
initWithNibName:@"NewsDetailController" bundle:nil];
// store new details in the detail controller; e.g.:
viewController.navigationItem.title = [self appDelegate].currentlySelectedBlogItem;
viewController.textView = [self appDelegate].currentDetails;
[self.navigationController pushViewController:viewController // vc retainCount is 2
animated:YES];
[release viewController]; // vc retainCount is 1
By releasing the new controller in the last line, we reduce its retain count to 1. Now the new controller is only retained by the stack, so when the stack is popped, the new controller will be dealloced.
If none of the above is helpful, please answer all the questions as best you can and post the indicated code, ok?
- Ray