detect current active subview of a navigation controller

i have a navigation controlle开发者_开发技巧r. i want to runa background thread on that controller which checks which subview is loaded currently in the navigation controller. loaded means tha active viewable subview.

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You don't have to (or should) use a background thread for this. Simply set the navigation controller's delegate and implement the method

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated

You can then store the currently active view controller in an instance variable.

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there is a UINavigationController property for that (from here):

topViewController

The view controller at the top of the navigation stack. (read-only)

@property(nonatomic, readonly, retain) UIViewController *topViewController

simply do:

UIViewController* topController = navigationController.topViewController;

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for (UIView *view in self.navigationController.view.subviews) 
{
}

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for (UINavigationController *view in self.view.subviews) { }