Question

I need to reload the data in a view controller when it’s tabbar is clicked.

I am using the UITabBarControllerDelegate method as below:

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    if (tabBarController.selectedIndex == 3) 
    {
        [(SomeViewController *)viewController getData];
    }
}

where ‘getData’ is an instance method in SomeViewController class. However when I run my app, I get the following error

2011-07-01 02:12:11.193 onethingaday[19169:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UINavigationController getData]: unrecognized selector sent to instance 0x600d500'

Can anyone advise me how I can overcome this issue? I just need to trigger the ‘getData’ method when tabbarcontroller.selected index ==3

Answer 1

It seems to me from the error message you get, that you use a UINavigationController in your tab controller; in this case, you cannot send directly the getData message to it; you should first find out which view controller under the UINavigationController should receive that message. (This is not actually related to the tab bar selectedIndex)

I don’t know how your UINavigationController is organized, but you could do:

 - (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController {
     if (tabBarController.selectedIndex == 3) {

   //-- option 1: getData goes to the first view controller in the UINavigationController:
         [[(SomeViewController*)[(UINavigationController*)viewController topViewController] getData];

   //-- option 2: getData goes to the last view controller in the UINavigationController (the visible one):
         [[(SomeViewController*)[(UINavigationController*)viewController visibleViewController] getData];

     }
 }

If you give more details about the organization of your UINavigationController I can help further identifying the right option.

Anyway, as you can see from the casts, there is something that is not fully ok with your design. I would strongly suggest using a notification for that. I.e., your SomeViewController registers itself for a notification of a given type :

 [[NSNotificationCenter defaultCenter] addObserver:self 
                             selector:@selector(someSelector:) 
                             name:ShouldGetDataNotification 
                             object:nil];

and the tab bar controller sends the notification for your controller to react upon:

 - (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController {
     if (tabBarController.selectedIndex == 3) {

      [[NSNotificationCenter defaultCenter] postNotificationName:ShouldGetDataNotification object:nil];
     }
  ....
}

Look at this post.