I am having trouble finding the solution to the problem of my UITableView crashing my applciation when it is scrolled. I am using the following code taken from the Apple documentation:
NSDictionary *categoryArray;
- (void)viewDidLoad
{
[super viewDidLoad];
UIColor *background = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:@"bg_black.png"]];
self.view.backgroundColor = background;
[background release];
MyApp *myapp = [[MyApp alloc ] init];
categoryArray = [myapp getCategory];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [categoryArray count];
}
- (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];
}
// Set up the cell...
NSString *cellValue = [categoryArray objectForKey: [NSString stringWithFormat:@"%d", indexPath.row+1]];
cell.textLabel.text = cellValue;
return cell;
}
Where the NSDictionary categoryArray looks like this (retrieved from a global singleton class):
{
1 = Bars;
2 = Nightclubs;
3 = Societies;
4 = Colleges;
5 = University;
}
I'm pretty sure it is some sort of memory allocation/recycled cell, but I can't see exactly where I am going wrong.
The error Thrown:
2011-11-23 21:29:01.888 WhatsOniPhone[3759:b303] -[__NSArrayM objectForKey:]: unrecognized selector sent to instance 0x4e7a3f0
2011-11-23 21:29:01.892 WhatsOniPhone[3759:b303] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM objectForKey:]: unrecognized selector sent to instance 0x4e7a3f0'
*** Call stack at first throw:
(
0 CoreFoundation 0x00dde5a9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x00f32313 objc_exception_throw + 44
2 CoreFoundation 0x00de00bb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
3 CoreFoundation 0x00d4f966 ___forwarding___ + 966
4 CoreFoundation 0x00d4f522 _CF_forwarding_prep_0 + 50
5 WhatsOniPhone 0x0000340a -[FirstViewController tableView:cellForRowAtIndexPath:] + 314
6 UIKit 0x000a5b98 -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] + 634
7 UIKit 0x0009b4cc -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:] + 75
8 UIKit 0x000b07f7 -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] + 1348
9 UIKit 0x000a890c -[UITableView layoutSubviews] + 242
10 QuartzCore 0x016c8a5a -[CALayer layoutSublayers] + 181
11 QuartzCore 0x016caddc CALayerLayoutIfNeeded + 220
12 QuartzCore 0x016700b4 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 310
13 QuartzCore 0x01671294 _ZN2CA11Transaction6commitEv + 292
14 QuartzCore 0x0167146d _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 99
15 CoreFoundation 0x00dbf89b __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 27
16 CoreFoundation 0x00d546e7 __CFRunLoopDoObservers + 295
17 CoreFoundation 0x00d1d1d7 __CFRunLoopRun + 1575
18 CoreFoundation 0x00d1c840 CFRunLoopRunSpecific + 208
19 CoreFoundation 0x00d1c761 CFRunLoopRunInMode + 97
20 GraphicsServices 0x010161c4 GSEventRunModal + 217
21 GraphicsServices 0x01016289 GSEventRun + 115
22 UIKit 0x0003ec93 UIApplicationMain + 1160
23 WhatsOniPhone 0x00002759 main + 121
24 WhatsOniPhone 0x000026d5 start + 53
)
terminate called throwing an exceptionsharedlibrary apply-load-rules all
The problem here is, among other things, likely memory management related as you predicted. I believe that the problem is that categoryArray
is being deallocated, and replaced in memory by a different object, in the case of your exception, an NSArray. The fix to this would be to retain categoryArray
, because for some reason right now it is not being retained properly by your view controller. So, whenever you assign categoryArray
, do categoryArray = [... retain]
instead of categoryArray = ...
. If you are assigning categoryArray
as a property, declare the property as @property (nonatomic, retain) NSDictionary * categoryArray
.
If your view controller keeps ownership of categoryArray
as it should, it will be necessary to release it in the dealloc method as follows:
- (void)dealloc {
// if using a property
self.categoryArray = nil;
// if not using a property
[categoryArray release];
...
[super dealloc];
}