Application (tableview) is crashing while scrolling - iphone

Question

I'm making an app which tries to read the information from the .plist file (put there parsed JSON).
The reading from file flows nice: got the array of dictionaries, but while trying to display it on tableview, the problems start. The initial view is loaded properly, but when I start scrolling, the app crashes.
#define DOCUMENTS [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject]
- (void)viewDidLoad
{
[super viewDidLoad];
NSString *filePathDocArray = [DOCUMENTS stringByAppendingPathComponent:#"filters.plist"];
NSString *filePathBundleArray = [[NSBundle mainBundle] pathForResource:#"filters" ofType:#"plist"];
if (![[NSFileManager defaultManager] fileExistsAtPath:filePathDocArray]) {
[[NSFileManager defaultManager] copyItemAtPath:filePathBundleArray toPath:filePathDocArray error:nil];
NSLog(#"File saved");
} else {
NSLog(#"File already exists");
filters = [NSArray arrayWithContentsOfFile:filePathDocArray];
}
}
Here I get all the info I need into filters array (checked by looping). Then:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [filters count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *myIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:myIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:myIdentifier];
}
NSInteger crow = indexPath.row;
NSDictionary *story = [filters objectAtIndex: crow];
cell.textLabel.text = [story objectForKey:#"Name"];
cell.detailTextLabel.text = [story objectForKey:#"Description"];
return cell;
}
#end
When the app starts everething is OK: I see the normel table view, but when I start scrolling it crashes
After series of breakpoint debugs I evaluated, that after the applications starts on Simulator, the link on array filters screws, so when I try to populate the next cell, the story dictionary can't be properly created.
What sort of problem it can be?
Here the console report:
2012-09-22 13:37:43.545 JSONExample[4559:207] -[__NSCFString
objectAtIndex:]: unrecognized selector sent to instance 0x6a083c0
2012-09-22 13:37:43.547 JSONExample[4559:207] *** Terminating app due
to uncaught exception 'NSInvalidArgumentException', reason:
'-[__NSCFString objectAtIndex:]: unrecognized selector sent to
instance 0x6a083c0'

Answer 1

are you using ARC??
if not then autorelease the cell first!!
and if filters is not a retain property.. kindly make it one and synthesize it and again if ARC not used then release it in the dealloc block.. that should do it i suppose..

Answer 2

-[NSCFString objectAtIndex:]: unrecognized selector seems to be the same problem.
Your 'filters' variable is an NSString/CFString at the time you call objectAtIndex: - not an array, as you would assume. The solution given in the question linked to is to retain your filters array whenever it's set.

Answer 3

If you wote property for the filters like #property (nonatomic, retain) NSArray *filters; you need to write like self.filters = [NSArray arrayWithContentsOfFile:filePathDocArray];
Else you need to write like filters = [[NSArray arrayWithContentsOfFile:filePathDocArray] retain];

Answer 4

You need to keep in mind another thing..
if you do this step
NSDictionary *story = [[filters objectAtIndex: crow]retain];
every time your cellForRowAtIndexPath is called the retain count would increase by 1. But you will delloc it only once.
So there will be memory leaks in your applications.
I suggest you go through the memory management guide once. its a small document. at max it will take one day of yours. But will feel more confident of what to do and what not to do.
http://developer.apple.com/library/ios/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/CFMemoryMgmt.pdf
Cheers!! And Happy Coding!!