Question

I’m new to Objective-C, and I can’t figure out why the NSString objects in my array of Car objects seem to have been released.

Here’s my Car.m class:

 #import 'Car.h' @implementation Car @synthesize categoryId;  - (id)initWithPrimaryKey:(NSInteger)pk categoryId:(NSNumber *)catId carName:(NSString *)n {     if (self = [super init]) {         primaryKey = pk;         categoryId = catId;         name = n;     }      return self; } - (void)dealloc {     [name release];     [categoryId release];      [super dealloc]; } - (NSInteger)primaryKey {     return primaryKey; } - (NSString *)name {     return name; } - (void)setName:(NSString *)aString {     if ((!name && !aString) || (name && aString && [name isEqualToString:aString])) return;     [name release];     name = [aString copy]; }  @end 

And here’s my Simple_TableViewController.m class. The listData instance variable is set correctly in viewDidLoad(). In the debugger, the NSString *name property of each array element is intact. Then, in every other method, listData is corrupt. It has all the Car elements with the correct primaryKey and categoryId values, but the NSString *name property is ‘Invalid.’

 #import 'Simple_TableViewController.h' @implementation Simple_TableViewController  - (void)viewDidLoad {            NSMutableArray *array = [[NSMutableArray alloc] init];     Database *database = [Database instance];      array = [database getAllCars];     [self setListData:array];     [array release]; } - (NSMutableArray *)listData {     return listData; } - (void)setListData:(NSMutableArray *)newListData {     if (listData != newListData) {         [listData release];         listData = [newListData mutableCopy];     } } - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {     return (interfaceOrientation == UIInterfaceOrientationPortrait); } - (void)didReceiveMemoryWarning {     [super didReceiveMemoryWarning]; } - (void)dealloc {     [listData release];     [super dealloc]; } - (NSInteger)tableView:(UITableView *)tableView  numberOfRowsInSection:(NSInteger)section {     return [listData count]; } - (UITableViewCell *)tableView:(UITableView *)tableView             cellForRowAtIndexPath:(NSIndexPath *)indexPath {     static NSString *SimpleTableIdentifier = @'SimpleTableIdentifier';      UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:SimpleTableIdentifier];     if (cell == nil) {         cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero                                                  reuseIdentifier:SimpleTableIdentifier] autorelease];     }      NSUInteger row = [indexPath row];     Car *car = [listData objectAtIndex:row];      cell.text = car.name;     cell.font = [UIFont boldSystemFontOfSize:17];      return cell; } - (NSInteger)tableView:(UITableView *)tableView indentationLevelForRowAtIndexPath:(NSIndexPath *)indexPath {     return 0; } - (NSIndexPath *)tableView:(UITableView *)tableView   willSelectRowAtIndexPath:(NSIndexPath *)indexPath {     NSInteger row = [indexPath row];     if (row == 0) {         return nil;     }      return indexPath; } - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {     NSUInteger row = [indexPath row];      NSString *message = [[NSString alloc] initWithFormat:@'You selected %@', [[listData objectAtIndex:row] name]];     UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@'Row Selected!'                                                                     message:message                                                                   delegate:nil                                                       cancelButtonTitle:@'Yes I Did'                                                       otherButtonTitles:nil];     [alert show];      [message release];     [alert release]; } - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {     return 35; }  @end 

I’ve fiddled with Zombie this and retain that until my fingers fell off. I did away with the @property (nonatomic, retain) and @synthesize stuff for the listData variable, and I still have the same problem.

Thanks in advance for any advice you have to offer!

Answer 1

In your initWithPrimaryKey:etc: method, you need to retain those values, or use the dot notation to assign them (assuming they are properties declared with the retain keyword). Try this:

 - (id)initWithPrimaryKey:(NSInteger)pk categoryId:(NSNumber *)catId carName:(NSString *)n {     if (self = [super init]) {         primaryKey = pk;         categoryId =[catId retain];         name = [n retain];     }

return self; 

}

Also, and this is just a style issue, you might consider slightly more verbose names than ‘n’ and ‘pk’. Your future-self will thank you.