Crash on UITableView when scrolling

Question

I'm developing a little text editor and I started using the Table View template, added code for listing on it the contents of the app Documents directory, and all is OK, I copied some files to the directory and the table view shows them, but when I start scrolling, it crashes. I think that something is being released when it doesn't have to. Here I left the code and the crash log :)

RootViewController.m

    NSFileManager *directoryContent;
- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [self listDumpFiles];
}
// Customize the number of sections in the table view.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}


// Customize the number of rows in the table view.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [directoryContent 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] autorelease];
    }

    // Configure the cell.
    cell.text = [directoryContent objectAtIndex:indexPath.row];
    return cell;
}
- (void)listDumpFiles {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    directoryContent = [[NSFileManager defaultManager] directoryContentsAtPath: documentsDirectory];

    NSLog(@"%@", documentsDirectory);
    return;
}

Crash log

2011-02-03 17:38:16.516 uNotes[15352:40b] /Users/pablo/Library/Application Support/iPhone Simulator/4.2/Applications/DF298F31-5723-4A1E-9EAA-3353C34BDCB2/Documents
2011-02-03 17:38:17.412 uNotes[15352:40b] -[NSCFString objectAtIndex:]: unrecognized selector sent to instance 0x9b243f0
2011-02-03 17:38:17.413 uNotes[15352:40b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString objectAtIndex:]: unrecognized selector sent to instance 0x9b243f0'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x00da7be9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x00efc5c2 objc_exception_throw + 47
    2   CoreFoundation                      0x00da96fb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    3   CoreFoundation                      0x00d19366 ___forwarding___ + 966
    4   CoreFoundation                      0x00d18f22 _CF_forwarding_prep_0 + 50
    5   uNotes                              0x0000238c -[RootViewController tableView:cellForRowAtIndexPath:] + 216
    6   UIKit                               0x003247fa -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] + 634
    7   UIKit                               0x0031a77f -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:] + 75
    8   UIKit                               0x0032f450 -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] + 1561
    9   UIKit                               0x00327538 -[UITableView layoutSubviews] + 242
    10  QuartzCore                          0x01c65451 -[CALayer layoutSublayers] + 181
    11  QuartzCore                          0x01c6517c CALayerLayoutIfNeeded + 220
    12  QuartzCore                          0x01c5e37c _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 310
    13  QuartzCore                          0x01c5e0d0 _ZN2CA11Transaction6commitEv + 292
    14  QuartzCore                          0x01c8e7d5 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 99
    15  CoreFoundation                      0x00d88fbb __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 27
    16  CoreFoundation                      0x00d1e0e7 __CFRunLoopDoObservers + 295
    17  CoreFoundation                      0x00ce6bd7 __CFRunLoopRun + 1575
    18  CoreFoundation                      0x00ce6240 CFRunLoopRunSpecific + 208
    19  CoreFoundation                      0x00ce6161 CFRunLoopRunInMode + 97
    20  GraphicsServices                    0x016dc268 GSEventRunModal + 217
    21  GraphicsServices                    0x016dc32d GSEventRun + 115
    22  UIKit                               0x002bf42e UIApplicationMain + 1160
    23  uNotes                              0x00001fc0 main + 102
    24  uNotes                              0x00001f51 start + 53
)
terminate called after throwing an instance of 'NSException'
Program received signal:  “SIGABRT”.
(gdb) 

Answer 1

According to the stack trace you are attempting to call objectAtIndex: on a String. Probably a memory management issue. Enable zombies to get more information about the object it is being called on.

UPDATE

It is probably this line

directoryContent = [[NSFileManager defaultManager] directoryContentsAtPath: documentsDirectory];

I think directoryContentsAtPath: returns an autoreleased object. If you have directoryContent set up as a @property(nonatomic, retain) in your header you can set it using self.directoryContent = [[NSFileManager defaultManager] directoryContentsAtPath: documentsDirectory]; and it will automatically retain the object returned by NSFileManager, otherwise you could call directoryContent = [[[NSFileManager defaultManager] directoryContentsAtPath: documentsDirectory] retain]; but be sure to release that object when you no longer need it.