Xcode 4.2 with Storyboard: Program received signal: “EXC_BAD_ACCESS”

Question

I'm implementing a simple app with storyboard which has a button from a "normal" View to a tableView:

Bigger picture here.

First I put the Navigation View into the storyboard and put a button into the RootView (The View "Welcome!". Then I put a tableView into storyboard and linked both pages with a Locations- Button in Storyboard (- until then I didn't write any code). Everything worked until then. But then I created a LocationsViewController for the TableView, because I wanted to fill the table view cell with data.

LocationsViewController.m:

#import "LocationsViewController.h"



@interface LocationsViewController ()
{
    NSArray* locations; //list of cities in our table
}
@end 






@implementation LocationsViewController


- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;

    locations = [NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil];

}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
#warning Potentially incomplete method implementation.
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
#warning Incomplete method implementation.
    // Return the number of rows in the section.
    return [locations count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:
                UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    // Configure the cell...

    [cell.textLabel setText:[locations objectAtIndex:indexPath.row]];
    return cell;
}

/*
 // Override to support conditional editing of the table view.
 - (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
 {
 // Return NO if you do not want the specified item to be editable.
 return YES;
 }
 */

/*
 // Override to support editing the table view.
 - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
 {
 if (editingStyle == UITableViewCellEditingStyleDelete) {
 // Delete the row from the data source
 [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
 }   
 else if (editingStyle == UITableViewCellEditingStyleInsert) {
 // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
 }   
 }
 */

/*
 // Override to support rearranging the table view.
 - (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
 {
 }
 */

/*
 // Override to support conditional rearranging of the table view.
 - (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
 {
 // Return NO if you do not want the item to be re-orderable.
 return YES;
 }
 */

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Navigation logic may go here. Create and push another view controller.
    /*
     <#DetailViewController#> *detailViewController = [[<#DetailViewController#> alloc] initWithNibName:@"<#Nib name#>" bundle:nil];
     // ...
     // Pass the selected object to the new view controller.
     [self.navigationController pushViewController:detailViewController animated:YES];
     [detailViewController release];
     */
}

@end

LocationsViewController.h:

#import <UIKit/UIKit.h>

@interface LocationsViewController : UITableViewController

@end

Since I declared this Class as the CustomClass for the TableView, pressing the button doesn't work anymore. While running the application on the iPhone Simulator and pressing the button, the application freezes and I get the message: Program received signal: “EXC_BAD_ACCESS”.

I read that the problem is a memory management bug in the code. I enabled the Zombie-Thing and got the message at the point return [locations count];with the console message [__NSArrayI count]: message sent to deallocated instance 0x6869460. So it's deallocating somewhere? How to solve the problem? Any help is appreciated!

Answer 1

One possibility is to use an property

in .h

@property (copy, nonatomic) NSArray *locations;

in .m

@synthesize locations;
- (void)viewDidLoad
{
    [super viewDidLoad];
    self.locations = [NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil];

}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [self.locations count];
}

Answer 2

First:

locations = [NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil];

[NSArray arrayWithObjects...] returns an autoreleased object and as you're setting it directly to your instance variable, you need to retain it:

locations = [[NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil] retain];

Note:It's a good practice to use properties instead of instance variables.

Second:

cell = [[UITableViewCell alloc] initWithStyle:
                UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];

According to the memory management rules alloc init returns a retained object, so you'll leak here. Change it to:

cell = [[[UITableViewCell alloc] initWithStyle:
                UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];