Using and updating a NSMutableString in AppDelegate for two viewcontrollers - xcode

Question

I have a NSMutableString defined in my AppDelegate.h file.
//AppDelegate.h
#interface AppDelegate : UIResponder <UIApplicationDelegate>{
#public
NSMutableString *nidForDetailDisplay;
}
Then I set this string in my ViewController.m file. I am storing a string (nidForDetailDisplay) to pass from a tableview to detailview.
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
rowNumber = indexPath.row;
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
// this is where I set the string to a string of text
appDelegate->theNidForDetailDisplay = [arrayOfNids objectAtIndex:rowNumber];
UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
UIViewController *detailViewController;
DetailViewController *detail = [self.storyboard instantiateViewControllerWithIdentifier:#"detail"];
[self.navigationController pushViewController:detail animated:YES];
}
In ViewController, when I log theNidForDetailDisplay, I get the correct string.
Next, I try to access this updated NSMutableString (nidForDetailDisplay) in the subsequent DetailViewController
-(void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
NSMutableString *storyid;
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
appDelegate->theNidOnDetailDisplay = storyid;
}
However, when I print the string (storyid) or (theNidOnDetailDisplay) they both return null.
Am I missing something here? Should I be using instance variables?
Thanks in advance.

Answer 1

Don't use your AppDelegate to pass data. Add a property to the detail view controller and assign the value to the property.
on DetailViewController:
#property (nonatomic) NSMutableString * nid;
The assign it before you present:
DetailViewController *detail = [self.storyboard instantiateViewControllerWithIdentifier:#"detail"];
detail.nid = [arrayOfNids objectAtIndex:rowNumber];
[self.navigationController pushViewController:detail animated:YES];