[__NSCFString count]: unrecognized selector sent to instance 0x60400043f9c0 - ios

Question

I am developing an iOS App. When I try to get the number of cells for section using a NSMutableArray, I get
[__NSCFString count]: unrecognized selector sent to instance
0x60400043f9c0.
Please help. Here is the code:
for (NSDictionary *dict in _array) {
NSString *dic = [dict objectForKey:#"product_base"];
if (dic == nil) {
}else{
[_productfliters addObject:dic];
}
NSString *dicMaterial = [dict valueForKey:#"product_material"];
if (dicMaterial == nil) {
}else{
[_productfliters addObject:dicMaterial];
}
// NSMutableDictionary *value = [[NSMutableDictionary alloc]init];
// [value setValue:[dict valueForKey:#"product_size"] forKey:#"ABC"];
NSString *dicSize = [dict valueForKey:#"product_size"];
[_productfliters addObject:dicSize];
}
self.sectionNames =[_arrayHeading mutableCopy];
self.sectionItems =[_productfliters mutableCopy];
NSLog(#"%#",self.sectionItems);
_tableview.tableFooterView = [[UIView alloc] initWithFrame:CGRectZero];
_tableview.rowHeight = UITableViewAutomaticDimension;
_tableview.estimatedRowHeight = 100;
self.expandedSectionHeaderNumber = -1;
[_tableview reloadData];
- (void)tableViewExpandSection:(NSInteger)section withImage:(UIImageView *)imageView {
NSArray *sectionData = [self.sectionItems objectAtIndex:section];
if (sectionData.count == 0) { //Error this part app crash NSCFString count
self.expandedSectionHeaderNumber = -1;
return;
} else {
[UIView animateWithDuration:0.4 animations:^{
imageView.transform = CGAffineTransformMakeRotation((180.0 * M_PI) / 180.0);
}];
NSMutableArray *arrayOfIndexPaths = [NSMutableArray array];
for (int i=0; i< sectionData.count; i++) {
NSIndexPath *index = [NSIndexPath indexPathForRow:i inSection:section];
[arrayOfIndexPaths addObject:index];
}
self.expandedSectionHeaderNumber = section;
[_tableview beginUpdates];
[_tableview insertRowsAtIndexPaths:arrayOfIndexPaths withRowAnimation: UITableViewRowAnimationFade];
[_tableview endUpdates];
}
}

Answer 1

You unload strings and put them into _productfliters:
for (NSDictionary *dict in _array) {
NSString *dic = [dict objectForKey:#"product_base"];
if (dic == nil) {
}else{
[_productfliters addObject:dic];
}
...
You then assign that to sectionItems:
self.sectionItems =[_productfliters mutableCopy];
You then extract one of those strings, but call it an array (even though you put strings in there, so it's a string):
NSArray *sectionData = [self.sectionItems objectAtIndex:section];
Just because you say NSArray here doesn't make it so. You're just telling the compiler what you expect to be true. objectAtIndex: return id ("any object"). It trusts you when you say it's an NSArray, but it isn't true.
You then call .count on a NSString and crash.
It's unclear what you're actually trying to do here, but you have an array of strings, not an array of arrays.
Note that ObjC has a new feature called lightweight generics that would possibly have caught this mistake. Had you declared sectionNames as either NSArray<NSString *>* or NSArray<NSArray<NSString *>*>* (depending on which one you wanted this to be), the compiler probably would have thrown a warning (maybe even an error). Lightweight generics are nowhere near as powerful as Swift's generics, but they can catch some type mismatches like this.