objective-c -[__NSCFNumber length]: unrecognized selector sent to instance - ios

Question

I'm working on an iOS app with collectionView in objective-c and I have an error.
Below code is for feeding each cell with data(image in this case).
I pick up an image name from two dimensional array in Model class, and display it.
I made up a new array to prevent from duplication of image display by changing value in the array from '0' to '1' so next time can avoid display '1' marked image.
I succeeded initial setting all arrays with NSInteger 0, with replaceObjectAtIndex:withObject: method in a 'ViewDidLaod' method, however, I have an error when I want to change the value into '1' in the array with replaceObjectAtIndex:withObject:, the same method I used in the 'ViewDidLaod' method.
I already searched google and stack but people who got the same problem used immutable array, that's why they had an issue, but I have mutable array in my code. Please help me.
The error message is below:
2015-04-13 03:55:25.824 InfanTree[4474:166010] -[__NSCFNumber length]: unrecognized selector sent to instance 0xb000000000000002
2015-04-13 03:55:25.846 InfanTree[4474:166010] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber length]: unrecognized selector sent to instance 0xb000000000000002'
*** First throw call stack:
(
0 CoreFoundation 0x000000010826fa75 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x0000000107f08bb7 objc_exception_throw + 45
2 CoreFoundation 0x0000000108276d1d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3 CoreFoundation 0x00000001081ce9dc ___forwarding___ + 988
4 CoreFoundation 0x00000001081ce578 _CF_forwarding_prep_0 + 120
5 UIKit 0x0000000108f13f06 +[_UIAssetManager createAssetNamed:fromBundle:] + 67
6 UIKit 0x00000001088d4f60 +[UIImage imageNamed:inBundle:compatibleWithTraitCollection:] + 221
7 InfanTree 0x00000001079c92d0 -[ViewController collectionView:cellForItemAtIndexPath:] + 512
8 UIKit 0x0000000108ed1fab -[UICollectionView _createPreparedCellForItemAtIndexPath:withLayoutAttributes:applyAttributes:] + 244
9 UIKit 0x0000000108ed36e4 -[UICollectionView _updateVisibleCellsNow:] + 3445
10 UIKit 0x0000000108ed7391 -[UICollectionView layoutSubviews] + 243
11 UIKit 0x000000010891c1c3 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 521
12 QuartzCore 0x000000010cc5ac58 -[CALayer layoutSublayers] + 150
13 QuartzCore 0x000000010cc4f87e _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
14 QuartzCore 0x000000010cc4f6ee _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
15 QuartzCore 0x000000010cbbd36e _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 242
16 QuartzCore 0x000000010cbbe482 _ZN2CA11Transaction6commitEv + 390
17 UIKit 0x00000001088a068d -[UIApplication _reportMainSceneUpdateFinished:] + 44
18 UIKit 0x00000001088a1375 -[UIApplication _runWithMainScene:transitionContext:completion:] + 2684
19 UIKit 0x000000010889fd35 -[UIApplication workspaceDidEndTransaction:] + 179
20 FrontBoardServices 0x000000010bd92243 __31-[FBSSerialQueue performAsync:]_block_invoke + 16
21 CoreFoundation 0x00000001081a4c7c __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
22 CoreFoundation 0x000000010819a9c5 __CFRunLoopDoBlocks + 341
23 CoreFoundation 0x000000010819a183 __CFRunLoopRun + 851
24 CoreFoundation 0x0000000108199bc6 CFRunLoopRunSpecific + 470
25 UIKit 0x000000010889f7a2 -[UIApplication _run] + 413
26 UIKit 0x00000001088a2580 UIApplicationMain + 1282
27 InfanTree 0x00000001079d19d3 main + 115
28 libdyld.dylib 0x000000010aa60145 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
Whole code is here
Below is part of my code.
#interface ViewController ()<UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout>
{
DataModel *_data;
// save the indexPath value itself of the picture which is selected at specific index path
NSMutableArray *_displayedImageIndexPathHistory;
// save 1 for the first rendering so next time can avoid to be selected
NSMutableArray *_isSelectedBefore;
// save 1 if rendered at least once so can avoid duplication
NSMutableArray *_preventDuplication;
}
#end
#implementation ViewController
.
.
.
- (void)viewDidLoad {
[super viewDidLoad];
.
.
.
// _data.imageSet is a two dimensional 'MUTABLE' array which has 'MUTABLE' arrays in it.
// Declared in a Model class. Each element has NSString *imageName.png.
_preventDuplication = [_data.imageSet mutableCopy];
_displayedImageIndexPathHistory = [_data.imageSet mutableCopy];
_isSelectedBefore = [_data.imageSet mutableCopy];
// set all arrays with 0
NSInteger sectionNum = [_data.imageSet count];
NSNumber *defaultNumber = [NSNumber numberWithInt:0];
for (NSInteger i = 0; i < sectionNum; i++) {
for (NSInteger j = 0; j < [_data.imageSet[i] count]; j++) {
[_displayedImageIndexPathHistory[i] replaceObjectAtIndex:j withObject:defaultNumber];
[_isSelectedBefore[i] replaceObjectAtIndex:j withObject:defaultNumber];
[_preventDuplication[i] replaceObjectAtIndex:j withObject:defaultNumber];
}
}
.
.
.
}
.
.
.
-(UICollectionViewCell *) collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
CollectionViewCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:#"Cell" forIndexPath:indexPath];
NSNumber *defaultNumber = [NSNumber numberWithInt:0];
NSNumber *markingNumber = [NSNumber numberWithInt:1];
if (indexPath.row == 0) {
cell.cellImageView.image = [UIImage imageNamed:[_data.imageSet[indexPath.section] objectAtIndex:indexPath.row]];
// **Have error at this sentence!!**
[_preventDuplication[indexPath.section] replaceObjectAtIndex:indexPath.row withObject: markingNumber];
}
else {
.
.
.
}
.
.
return cell;
}
Thanks in advance.

Answer 1

Your code has the expression:
[UIImage imageNamed:[_data.imageSet[indexPath.section] objectAtIndex:indexPath.row]]
It would seem that this part:
[_data.imageSet[indexPath.section] objectAtIndex:indexPath.row]
Is producing an instance of NSNumber, not an instance of NSString. Of course, +[UIImage imageNamed:] requires its argument to be a string. It's apparently invoking -length on it. Since NSNumber doesn't respond to -length, you get that exception and crash.