iOS Master-Detail app: defining protocol, delegates

Question

In the master-detail application template (using ARC, storyboards) in XCode 4.3.2, I am trying to change (more specifically replace) the detail view when an item in master table view is selected. I am trying to implement delegates/protocols for this.

What I am confused about is - which class should implement the methods defined in protocol - master or detail?

Having the detail view implement the protocol method makes sense to me since, I'll be push/popping the view controllers in detail view based on the selection (passed as a string from master via the protocol method).

Here's what I tried

1) Defined the protocol in MasterViewController.h

@protocol MasterViewDelegate <NSObject>
- (void)masterSelectionChanged:(NSString *)selection;
@end
@interface MasterViewController:UIViewContoller
@property (nonatomic, weak) id <MasterViewDelegate> delegate

2) in MasterViewController.m

@synthesize delegate;
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    [delegate masterSelectionChanged:@"Some string based on indexPath.row"];
}

3) in DetailViewController.h

#import "MasterViewController.m"
@interface DetailViewController:UINavigationController <MasterViewDelegate>
@end

4) in DetailViewController.m

#pragma mark - MasterViewDelegate
- (void)masterSelectionChanged:(NSString *)selection
{
    NSLog(@"the selection is: %s", selection);
    // WIll push/pop view over here, may be perform segues based on selection
}

In this process, upon selecting the rows in master table, nothing happened. No crash, no display of log, no error while building either. What did I miss over here?

1) Are you talking about the iPad or iPhone (the master/detail templates are very different in each one) 2) Have you actually set the delegate property anywhere, or just defined it? — jrturton, May 08 '12 at 10:47
@jrturton - I am trying this for the iPad one. defining the `delegate` property?? May be that's what I missed. Where should I define the delegate property? — vikmalhotra, May 08 '12 at 10:51

jrturton · Accepted Answer · 2012-05-08T12:22:48.877

0

You need to set the delegate property - at the moment it will be nil so nothing happens when you send messages to it. In the iPad template you can do this as follows, in the viewDidLoad of your detail view controller:

[super viewDidLoad];
if (self.splitViewController) // Means this won't be called if you use this code on iPhone too.
{
    // According to comments your master controller is embedded in a nav controller
    UINavigationController *nav = (UINavigationController*)[self.splitViewController.viewControllers objectAtIndex:0];
    // I am assuming it is the root view controller
    MasterViewController *master = (MasterViewController*)nav.rootViewController;
    // Finally set the delegate
    master.delegate = self;
}

edited May 08 '12 at 12:22

answered May 08 '12 at 10:57

jrturton

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I tried this but the method defined in protocol is still not being invoked. the delegate is nil when the row is selected. – vikmalhotra May 08 '12 at 11:12
what happens if you log master.delegate after the assignment in my code above?: `NSLog(@"master : %@ delegate: %@ self: %@",master,master.delegate,self);` – jrturton May 08 '12 at 11:24
it shows - `master: delegate: self: ` – vikmalhotra May 08 '12 at 11:30
Ah! Your master view controller is embedded in a navigation controller. You'll need to get a pointer to the actual controller itself then - presumably the `rootViewController` of the navigation controller? – jrturton May 08 '12 at 12:19
@jrjurton - also I played around with the solution over here which worked fine as well http://stackoverflow.com/q/10019422/206613 – vikmalhotra May 08 '12 at 14:05

iOS Master-Detail app: defining protocol, delegates

1 Answers1