Trouble tracking down EXC_BAD_ACCESS error

Question

I'm working on a simple drill down table view app with a navigation view controller and a table view controller. I'm getting an EXCBADACCESS crash when I select a particular table cell view, press back to the previous view in the hierarchy using the navigation item, and then reselecting the same view using the same cell again.
In the .h file, I have:
@interface RootViewController : UITableViewController
UITableViewCell* tableViewCell;
NSMutableArray* listOfItems;
NSDictionary* data;
NSArray* tableDataSource;
@property (nonatomic, assign) IBOutlet UITableViewCell* tableViewCell;
@property (nonatomic, retain) NSDictionary* data;
@property (nonatomic, retain) NSArray* tableDataSource;
And in the .m file:
- (void)viewDidLoad
[super viewDidLoad];
NSString *Path = [[NSBundle mainBundle] bundlePath];
NSString *DataPath = [Path stringByAppendingPathComponent:@"data.plist"];
NSDictionary *tempDict = [[NSDictionary alloc] initWithContentsOfFile:DataPath];
self.data = tempDict;
[tempDict release];
//Initialize our table data source
NSArray *tempArray = [[NSArray alloc] init];
self.tableDataSource = tempArray;
[tempArray release];
self.tableDataSource = [data objectForKey:@"Children"];
self.navigationItem.title = [data objectForKey:@"Title"];
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
NSDictionary* dictionary = [self.tableDataSource objectAtIndex:indexPath.row];
NSArray* children = [dictionary objectForKey:@"Children"];
if(children)
//Prepare to tableview.
RootViewController* rootViewController = [[RootViewController alloc] initWithNibName:@"RootViewController" bundle:[NSBundle mainBundle]];
//Push the new table view on the stack
[self.navigationController pushViewController:rootViewController animated:YES];
NSString* temp = [dictionary objectForKey:@"Title"];
rootViewController.navigationItem.title = [dictionary objectForKey:@"Title"];
rootViewController.tableDataSource = children;
[rootViewController release];
[children release];
The callstack I get seems to vary, but a lot of the time it is related to the fact that it is trying to set the property of a variable that has already been released. When a callstack does appear, it is often related to the setter in the line:
rootViewController.tableDataSource = children;
I've checked the code using NSZombie and MallocStackLogging, but the invalid memory dereferenced seems to vary each time, sometimes it corresponds to rootViewController.data, other times to rootViewController.tableDataSource and sometimes it doesn't correspond to either.
Essentially, the problem seems to be that when the RootViewController for the selected detail view is created, it's member variables are immediately released, although this only seems to be a problem when detail view is loaded a second time after the user has pressed back. The first time the view is selected, it works fine.
I've added a debugging NSDictionary and NSArray category to and, so that I can breakpoint the release method. However, I've checked the addresses of the data and tableDataSource for the rootViewController that is created in didSelectRowAtIndexPath, and compared these with the NSArray self pointers as they are released (the NSDictionary release method is never called), and they never match, so I'm not sure where the problem attribute is being released.
If anybody has any ideas about what this could be, or has any suggestions about other things I could try, I'd be very grateful.

Answer 1

Thanks for explaining the relationship between this thread and the previous one. That info helped.
The cause of the crash was the release of the 'children' array in the last statement of tableView:didSelectRowAtIndexPath:. Prior to that release, the array was retained by its parent dictionary, and by the tableDataSource property of the level-2 controller. After the release, the array's retain count was reduced to one, so when the level-2 controller was popped, the array was dealloced, invalidating that branch of its parent dictionary.
I also made a few other corrections to the code. The most lengthy of these was to keep viewDidLoad from loading the plist more than once. That problem wasn't causing a data error though, since for controllers above level 1, the tableDataSource and navigationItem.title are set by the previous controller after viewDidLoad runs. I.e. the correction just saves an unnecessary file read, but doesn't affect the outcome.
// RootViewController.h
@interface RootViewController : UITableViewController
UITableViewCell* tableViewCell;
// NSMutableArray* listOfItems; // <-- not used
NSDictionary* data;
NSArray* tableDataSource;
int level; // <-- level of controller on the nav stack
@property (nonatomic, assign) IBOutlet UITableViewCell* tableViewCell;
@property (nonatomic, retain) NSDictionary* data;
@property (nonatomic, retain) NSArray* tableDataSource;
@end
// RootViewController.m
#import "RootViewController.h"
@implementation RootViewController
@synthesize tableViewCell, data, tableDataSource;
- (void)viewDidLoad
[super viewDidLoad];
// --> only the level-1 controller should load the plist
level = [self.navigationController.viewControllers count];
NSLog(@"%s: level=%d", _func_, level);
if (level <= 1) {
NSString *Path = [[NSBundle mainBundle] bundlePath];
NSString *DataPath = [Path stringByAppendingPathComponent:@"data.plist"];
NSDictionary *tempDict = [[NSDictionary alloc] initWithContentsOfFile:DataPath];
self.data = tempDict;
[tempDict release];
// --> newly alloced array isn't used
//Initialize our table data source
// NSArray *tempArray = [[NSArray alloc] init];
// self.tableDataSource = tempArray;
// [tempArray release];
self.tableDataSource = [data objectForKey:@"Children"];
self.navigationItem.title = [data objectForKey:@"Title"];
else
;// tableDataSource and navigationItem.title are set by previous controller
#pragma mark Table view methods
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
// Customize the number of rows in the table view.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [tableDataSource count];
// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
static NSString *CellIdentifier = @"TableViewCell";
UITableViewCell *cell = (UITableViewCell*)
[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil)
// NSLog(@"%s: level=%d row=%d", _func_, level, indexPath.row);
[[NSBundle mainBundle] loadNibNamed:@"TableViewCell" owner:self options:nil];
cell = tableViewCell;
tableViewCell = nil;
// Set up the cell...
NSDictionary *dictionary = [self.tableDataSource objectAtIndex:indexPath.row];
cell.textLabel.text = [dictionary objectForKey:@"Title"];
return cell;
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
// NSLog(@"%s: tableDataSource=%@", _func_, self.tableDataSource);
NSDictionary* dictionary = [self.tableDataSource objectAtIndex:indexPath.row];
// NSLog(@"%s: dictionary=%@", _func_, dictionary);
NSArray* children = [dictionary objectForKey:@"Children"];
// NSLog(@"%s: children=%@", _func_, children);
if(children)
//Prepare to tableview.
RootViewController* rootViewController = [[RootViewController alloc]
initWithNibName:@"RootViewController" bundle:[NSBundle mainBundle]];
//Push the new table view on the stack
[self.navigationController pushViewController:rootViewController animated:YES];
// NSLog(@"%s: stack=%@", _func_, self.navigationController.viewControllers);
// NSString* temp = [dictionary objectForKey:@"Title"]; // <-- not used
rootViewController.navigationItem.title = [dictionary objectForKey:@"Title"];
rootViewController.tableDataSource = children;
[rootViewController release];
// [children release]; // <-- must not release - owned by root dictionary
- (void)dealloc {
NSLog(@"%s: level=%d", _func_, level);
[tableDataSource release];
[data release];
[super dealloc];
@end
- Ray