error on Key Value coding when using prepareForSegue - ios

Question

I am using the following to create a reference to a view controller in my code like this:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if([segue.identifier isEqualToString:#"detailSegue"]){
NSIndexPath *indexPath=[self.tableView indexPathForSelectedRow];
TRDetailViewController *vc=segue.destinationViewController;
vc.item=self.items[indexPath.row];
[vc setValue:self forKeyPath:#"delegate"];
[vc setValue:indexPath.row forKeyPath:#"itemIndex"];
}
}
and this is declared as in TRDetailViewController
#interface TRDetailViewController : UIViewController
#property (weak, nonatomic) IBOutlet UILabel *detailLabel;
#property NSString *item;
#property (nonatomic, weak)id delegate;
#property NSInteger itemIndex;
- (IBAction)deleteItem:(id)sender;
#end
but I get the following error
and I'm not sure why. I am trying to pass the location in an index of the cell selected in a UITableView. If a better way, please let me know. Why am I getting this error?
thx

Answer 1

setValue:forKey: is expecting an object for its value argument and you are passing it a primitive (in this case, an integer). You can work around this by amending your method to read as follows:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if([segue.identifier isEqualToString:#"detailSegue"]){
NSIndexPath *indexPath=[self.tableView indexPathForSelectedRow];
TRDetailViewController *vc=segue.destinationViewController;
vc.item=self.items[indexPath.row];
[vc setValue:self forKeyPath:#"delegate"];
[vc setValue:[NSNumber numberWithInt:indexPath.row] forKeyPath:#"itemIndex"];
}
}
And then access it like:
[[vc valueForKey:#"itemIndex"] intValue];

Answer 2

setValue:forKeyPath: requires an object (i.e. id) as first argument.
You are instead passing a NSInteger.
You will have to use an object type, which means to turn your itemIndex into a NSNumber.
Then you can store it using
[vc setValue:#(indexPath.row) forKeyPath:#"itemIndex"];
and retrieve it by
NSInteger myIndex = [vc valueForKey:#"itemIndex"].integerValue;