Get to UIViewController from UIView?

Question

Is there a built-in way to get from a UIView to its UIViewController? I know you can get from UIViewController to its UIView via [self view] but I was wondering if there is a reverse reference?

Answer 1

I don't think it's "bad" idea to find out who is the view controller for some cases. What could be a bad idea is to save the reference to this controller as it could change just as superviews change. In my case I have a getter that traverses the responder chain.

//.h

@property (nonatomic, readonly) UIViewController * viewController;

//.m

- (UIViewController *)viewController
{
    for (UIResponder * nextResponder = self.nextResponder;
         nextResponder;
         nextResponder = nextResponder.nextResponder)
    {
        if ([nextResponder isKindOfClass:[UIViewController class]])
            return (UIViewController *)nextResponder;
    }

    // Not found
    NSLog(@"%@ doesn't seem to have a viewController". self);
    return nil;
}

Answer 2

Swift 4 version

extension UIView {
var parentViewController: UIViewController? {
    var parentResponder: UIResponder? = self
    while parentResponder != nil {
        parentResponder = parentResponder!.next
        if let viewController = parentResponder as? UIViewController {
            return viewController
        }
    }
    return nil
}

Usage example

 if let parent = self.view.parentViewController{

 }

Answer 3

There is no way.

What I do is pass the UIViewController pointer to the UIView (or an appropriate inheritance). I'm sorry I can't help with the IB approach to the problem because I don't believe in IB.

To answer the first commenter: sometimes you do need to know who called you because it determines what you can do. For example with a database you might have read access only or read/write ...

Answer 4

Maybe I'm late here. But in this situation I don't like category (pollution). I love this way:

#define UIViewParentController(__view) ({ \
UIResponder *__responder = __view; \
while ([__responder isKindOfClass:[UIView class]]) \
__responder = [__responder nextResponder]; \
(UIViewController *)__responder; \
})

Answer 5

Another easy way is to have your own view class and add a property of the view controller in the view class. Usually the view controller creates the view and that is where the controller can set itself to the property. Basically it is instead of searching around (with a bit of hacking) for the controller, having the controller to set itself to the view - this is simple but makes sense because it is the controller that "controls" the view.

Answer 6

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;
- (id) traverseResponderChainForUIViewController;
@end

@implementation UIView (FindUIViewController)
- (UIViewController *) firstAvailableUIViewController {
    // convenience function for casting and to "mask" the recursive function
    return (UIViewController *)[self traverseResponderChainForUIViewController];
}

- (id) traverseResponderChainForUIViewController {
    id nextResponder = [self nextResponder];
    if ([nextResponder isKindOfClass:[UIViewController class]]) {
        return nextResponder;
    } else if ([nextResponder isKindOfClass:[UIView class]]) {
        return [nextResponder traverseResponderChainForUIViewController];
    } else {
        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];