passing nesting through segue nil on init methods but valid on viewdidload - ios

Question

I have made a segue passing a string which tells the next view controller which instance to parse the CoreData for. The problem is, I am using some code that calls init methods and the sent string is not initialized when it is called. However, the segue is working when I display the string in the destination view controller's viewDidLoad
- (id)init
{
self = [super init];
if (self)
{
[self initFakeData];
}
return self;
}
When that initFakeData method is called it sets up a graph and needs the exercise to hold a valid value
- (void)initFakeData
{
NSString *myExercise=exercise; //returns nil
if (myExercise==nil)
{
myExercise=#"Default";
}
}
Meanwhile...
-(void)viewDidLoad{
NSString *myExercise=exercise; //returns value
}
exercise is a property that is initialized by the previous view controller in a tableview
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
if ([segue.identifier isEqualToString:#"showGraph"]) {
JBLineChartViewController *destViewController = segue.destinationViewController;
NSString *myExericse=[NSString stringWithFormat:#"%#", [[_exercises valueForKey:#"exercise"]objectAtIndex:indexPath.row]];
NSLog(#"%#",myExericse);
destViewController.exercise = myExericse;
}
}

Answer 1

The behaviour is correct because during init the exercise in JBLineChartViewController was not set. If you need the exercise attribute in the init method to set certain behaviour that have to be before viewDidLoad, my suggestion is to not use segue but do a designated initWithExercise and push the controller in code. Maybe like this:
- (IBAction)chartButtonPressed:(id)sender {
JBLineChartViewController *vc = [[ShopViewController alloc]initWithExercise:#"EXERCISE_STRING_HERE"];
[self showViewController:vc sender:self];
}

Answer 2

The new view controller is allocated and initialized before prepareForSegue is called. Anything you need to do with CoreData should be done in viewDidLoad. Or you can do it later, e.g. in viewWillAppear or viewDidAppear.