Ios – UIViewController prevent view from unloading

Using the example posted by Brock, I modified it so that it is a category of UIView instead UIViewController and made it recursive so that any subview can (hopefully) find the parent UIViewController.

@interface UIView (FindUIViewController)
- (UIViewController *) firstAvailableUIViewController;
@end

@implementation UIView (FindUIViewController)
- (UIViewController *) firstAvailableUIViewController {
    UIResponder *responder = [self nextResponder];
    while (responder != nil) {
        if ([responder isKindOfClass:[UIViewController class]]) {
            return (UIViewController *)responder;
        }
        responder = [responder nextResponder];
    }
    return nil;
}

@end

To use this code, add it into an new class file (I named mine "UIKitCategories") and remove the class data... copy the @interface into the header, and the @implementation into the .m file. Then in your project, #import "UIKitCategories.h" and use within the UIView code:

// from a UIView subclass... returns nil if UIViewController not available
UIViewController * myController = [self firstAvailableUIViewController];

The view's window property is non-nil if a view is currently visible, so check the main view in the view controller:

Invoking the view method causes the view to load (if it is not loaded) which is unnecessary and may be undesirable. It would be better to check first to see if it is already loaded. I've added the call to isViewLoaded to avoid this problem.

if (viewController.isViewLoaded && viewController.view.window) {
    // viewController is visible
}

Since iOS9 it has became easier:

if viewController.viewIfLoaded?.window != nil {
    // viewController is visible
}

Or if you have a UINavigationController managing the view controllers, you could check its visibleViewController property instead.