如何将数据传递给嵌入在导航控制器中的集合视图控制器

Question

I want to pass integer value from MainViewController to CollectionViewController embedded in UINavigationViewController . The code is written in MainViewController.m file within prepareForSegue method. I am getting warning as:

Incompatible pointer types initializing ' CollectionViewController *' with an expression of type ' UIViewController * _Nullable'

The warning is for the code:

UINavigationController *navController = (UINavigationController*)[segue destinationViewController];

CollectionViewController *collectionVC = [navController topViewController];

For passing integer I am using:

[collectionVC setReceivedCategoryId:categoryIdToSend];

Answer 1

UINavigationController 's topViewController method returns an UIViewController object as shown is the Apple documentation . Cast the object and it will work.

 UINavigationController *navController = (UINavigationController*)[segue destinationViewController];

// Add the explicit cast
CollectionViewController *collectionVC = (CollectionViewController*)[navController topViewController];

Answer 2

[navController topViewController]; returns a UIViewController object. But we know that it is a CollectionViewController . So we add a typecast, like so :

CollectionViewController *collectionVC =(CollectionViewController*) [navController topViewController];