CODEWITHSUNDEEP
iphoneobjective-ciosdelegates
tazboy
tazboy

Reputation: 1754

Implementing delegation

I think I'm following how delegation works, here's the tutorial I followed, but I'm messing up somewhere. I'm expecting my delegate to NSLog but it's not. Can anyone find out what am I missing or doing wrong?

My MainViewController.h:

@interface MainViewController : UITableViewController < AddClassDelegate >

MainViewController.m:

- (void)cancelAddingClass {
    NSLog(@"Canceled Yo");
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

/*
 When a row is selected, the segue creates the detail view controller as the destination.
 Set the detail view controller's detail item to the item associated with the selected row.
 */
if ([[segue identifier] isEqualToString:@"addClassSegue"]) {

    UINavigationController *nc = (UINavigationController *)segue.destinationViewController;
    AddClassViewController *addClassVC = (AddClassViewController *)[nc.viewControllers objectAtIndex:0];
    addClassVC.delegate = self;
}

My modal view controller AddClassViewController.h:

@protocol AddClassDelegate <NSObject>
- (void)cancelAddingClass;
@end

@interface AddClassViewController : UITableViewController

@property (weak, nonatomic) id< AddClassDelegate > delegate;

- (IBAction)cancelButtonPressed:(id)sender;

AddClassViewController.m:

@synthesize delegate;

- (IBAction)cancelButtonPressed:(id)sender {
    [self.delegate cancelAddingClass];
}

cancelButtonPressed:

is hooked up to the modal view's Cancel button in Storyboard.

Upvotes: 2

Views: 633

Answers (3)

jrturton
jrturton

Reputation: 119292

Your code looks fine, which suggests the problem is somewhere we can't see. My guess is here:

AddClassViewController *addClassVC = [segue destinationViewController];
addClassVC.delegate = self;
NSLog(@"segued");

Have you embedded your modal view controller in a navigation controller? If so, destinationViewController gives you the navigation controller, not the AddClassViewController. Check what class addClassVC actually is in the debugger.

If it is a navigation controller, no problem, you just need to get to your actual VC using the .viewControllers property. On several lines to make it simpler to understand:

UINavigationController *nc = (UINavigationController *)segue.destinationViewController;
AddClassViewController *addClassVC = (AddClassViewController *)[nc.viewControllers objectAtIndex:0];
addClassVC.delegate = self;

You can do it in fewer lines but it's a mess of casting and nested brackets, which is harder to debug.

Upvotes: 2

Jim
Jim

Reputation: 73966

Is it possible your main view controller is being released? That would set the weak reference to nil and the message you send to your delegate would simply be ignored because you'd be messaging nil.

Upvotes: 0

Dee
Dee

Reputation: 1897

Everything is perfect. I haven't seen any issue. Keep break points everywhere and debug it.

Upvotes: -1

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