Only sometimes get EXC_BAD_ACCESS when setting uitabviewcontroller viewcontrollers - ios

Question

I'm trying to create and set VCs for my tab view controller. There is a next button in each VC that either opens the next tab or loads a new set of tabs when it reaches the end. Inside both Type1.m and Type2.m:
- (IBAction)next:(id)sender {
if (self.tabBarController.selectedIndex < [self.tabBarController.viewControllers count] - 1) {
self.tabBarController.selectedIndex += 1;
}
else {
// load nextData
NSLog(#"nextData: %#", nextData);
if (nextData == nil) {
// essentially stop the next button from working
return;
}
self.tabBarController.selectedIndex = 0U;
[self.tabBarController setTitle:[nextData display_name]];
[self.tabBarController setViewControllers:[nextData loadTabs]];
}
}
loadTabs is a method of the Data class (which is a Core Data NSManagedObject subclass with a category).
Inside ParentData+Helpers.m It looks like:
- (NSArray *)loadTabs {
NSMutableArray *mut = [NSMutableArray new];
for (SubData *d in self.datapoints) {
if ([d.field_x isEqual:#YES]) {
[mut addType1:d];
else {
[mut addType2:d];
}
return mut;
}
addType1 and addType2 are nearly identical in their fields, but have different implementations. They look like:
- (TypeVC *)addType1:(SubData *)data {
TypeVC *vc = [[TypeVC alloc] init];
vc.datapoint = data;
return vc;
}
where TypeVC is either Type1 or Type2
So now I have a table view and each cell has an associated ParentData which has an array of SubData objects. When selected, it loads a UITabViewController with Type1 and Type2 VCs.
inside TableVC.m:
- (void)- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[self performSegueWithIdentifier:#"toTabs" sender:self];
}
where toTabs leads to a UITabBarController in the storyboard.
In prepareForSegue:
UITabBarController presentedTabBarController = [segue destinationViewController];
[presentedTabBarController setTitle:self.selectedTitleName];
[presentedTabBarController setViewControllers:[self.selectedParentData loadTabs]];
So all that works fine.
So I run my app, get to the UITabBarController and the thing that should be there is. The first set of tabs has 2 tabs, so I hit next and it goes to the second one. I hit next, and it loads the next set of tabs and opens to the correct tab. I hit next, alls working good. I hit next four or five times, each time it works correctly. It doesnt matter if its Type1 or Type2, it works.
But then suddenly, I get to a specific one that has 2 tabs. It loads the first one (the one at index 0) and then I hit next. And suddenly I have EXC_BAD_ACCESS(code=1, address=0xWHATEVER) at the line self.tabBarController.selectedIndex += 1;. I don't understand why this would happen.