App crashing when scrolling TableView

My app is crashing when i scroll my TableView. First in my viewDidLoad method a load a dictionary from a file and for this dictionary i enumerate all keys.

 - (void)viewDidLoad {

     [super viewDidLoad];

     NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)objectAtIndex:0];      

     path = [rootPath stringByAppendingPathComponent:[NSString stringWithFormat:@"currency.archive"]]; 

     banks = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

     keys = [banks allKeys];

     // set date for last update 
     dayMonthYear.text = [banks objectForKey:@"Last Updated"];
}

In my cellForRowAtIndexPath i populate cells with data from that dictionary. Anyway when my app starts everything looks fine, first five rows are drawn correctly, but when i start to scroll my app crash. My idea is that the problem is with autoreleased object here, i tried to reta开发者_开发技巧in them and after using them to release ,but unsuccessful. DEBUGGER SHOWS THAT MY PROBLEM IS AT LINE WITH BOLD

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    NSString *CellIdentifier = [NSString stringWithFormat:@"Cell %d_%d",indexPath.section,indexPath.row];

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {      

        [[NSBundle mainBundle] loadNibNamed:@"CurrencyTableCell" owner:self options:nil];

        cell = currencyTableCell;

        //don't show selected cell
        cell.selectionStyle = UITableViewCellSelectionStyleNone;
        //set height
        self.cellHeight = cell.frame.size.height;
    }    

    // Fetch currency 
    NSString *currentCurrency = [keys objectAtIndex:indexPath.row];

    NSDictionary *fetchedCurrency = [banks objectForKey:currentCurrency];

    **NSString *name = [fetchedCurrency objectForKey:@"Currency Name"];**

    currencyTitle.text = name;

    NSString *charCode = [fetchedCurrency objectForKey:@"Code"];

    currencyCode.text = charCode;

    NSString* formattedNumber = [NSString stringWithFormat:@"%.02f",[[fetchedCurrency  objectForKey:@"Value"] floatValue]];

    if ([formattedNumber length] == 4) {
        formattedNumber = [NSString stringWithFormat:@"%@%@",@"0",formattedNumber];
    }

    buyPrice.text = formattedNumber;

    return cell;    
}

As a result from the discussion, [banks objectForKey:@"Last Updated"] gives you a NSString, not a NSDictionary!

You could get around this error by doing

if ([[banks objectForKey:currentCurrency] class] == [NSDictionary class]) { 
    ... rest of the code here .. 
}

Change your viewDidLoad with below code it will work

- (void)viewDidLoad {
     [super viewDidLoad];

     NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)objectAtIndex:0];      
     path = [rootPath stringByAppendingPathComponent:[NSString stringWithFormat:@"currency.archive"]]; 
     banks = [[NSDictionary alloc] initWithDictionary:[NSKeyedUnarchiver unarchiveObjectWithFile:path]];
     keys = [[NSArray alloc] initWithArray:[banks allKeys]];
     // set date for last update 
     dayMonthYear.text = [banks objectForKey:@"Last Updated"];
 }

-[NSCFString objectForKey:]: unrecognized selector sent to instance 0x4bab9c0

Your banks and keys variables aren't retained, as mentioned in another answer, but this isn't the error.

As per this error, your fetchedCurrency object is an NSString, not an NSDictionary. Check the format of your currency.archive file.