Issues with NSMutableArray and my table - iphone

Question

I'm trying to be able to insert an object into my table, but it crashes because of an uncaught exception whenever I hit the add button. It says
Attempt to insert row 0 into section 0, but there are only 0 rows in section 0 after the update
Here's my main view controller which handles all my table stuff...
#import "MasterViewController.h"
#import "DetailViewController.h"
#define kFileName #"steakNames.plist"
#interface MasterViewController () {
NSMutableArray *_objects;
}
#end
#implementation MasterViewController
#synthesize steakName;
- (NSString *)dataFilePath {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentationDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
return [documentsDirectory stringByAppendingPathComponent:kFileName];
}
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
self.title = NSLocalizedString(#"Master", #"Master");
}
return self;
}
- (void)viewDidLoad
{
NSString *filePath = [self dataFilePath];
if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
_objects = [[NSMutableArray alloc] initWithContentsOfFile:filePath];
}
UIApplication *app = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(applicationWillResignActive:) name:UIApplicationWillResignActiveNotification object:app];
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.navigationItem.leftBarButtonItem = self.editButtonItem;
UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:#selector(insertNewObject:)];
self.navigationItem.rightBarButtonItem = addButton;
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
- (void)insertNewObject:(id)sender
{
if (!steakName) {
steakName = #"No name";
}
[_objects insertObject:[self steakName] atIndex:0];
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];
[self.tableView insertRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
}
#pragma mark - Table View
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return _objects.count;
}
// Customize the appearance of table view cells.
- (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];
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
}
NSDate *object = [_objects objectAtIndex:indexPath.row];
cell.textLabel.text = [object description];
return cell;
}
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the specified item to be editable.
return YES;
}
- (void)tableView:(UITableView *)tableView commitEditingStyle: (UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete) {
[_objects removeObjectAtIndex:indexPath.row];
[tableView deleteRowsAtIndexPaths:#[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;
}
*/
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
if (!self.detailViewController) {
self.detailViewController = [[DetailViewController alloc] initWithNibName:#"DetailViewController" bundle:nil];
}
NSDate *object = [_objects objectAtIndex:indexPath.row];
self.detailViewController.detailItem = object;
[self.navigationController pushViewController:self.detailViewController animated:YES];
}
- (void)applicationWillResignActive:(NSNotification *)notification {
[_objects writeToFile:[self dataFilePath] atomically:YES];
}
#end

Answer 1

Most likely the cause of the error is that this returns 0:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return ...;
}
I would suggest that you first take a complete working example of table view with all its required methods and start from there.
Generally you need to implement these methods:
(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
(NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
So far there is no issue with any NSMutableArray, anyway you cannot insert an object at an index if the array does not yet have the number of objects, eg insert at index 4 but the array has only 2 objects. You can always add objects to NSMutableArray and increase the number of objects in this array.