Get the current first responder without using a private API

I submitted my app a little over a week ago and got the dreaded rejection email today. It tells me that my app cannot be accepted because I'm using a non-public API; specifically, it says,

The non-public API that is included in your application is firstResponder.

Now, the offending API call is actually a solution I found here on SO:

UIWindow *keyWindow = [[UIApplication sharedApplication] keyWindow];
UIView   *firstResponder = [keyWindow performSelector:@selector(firstResponder)];

How do I get the current first responder on the screen? I'm looking for a way that won't get my app rejected.

If your ultimate aim is just to resign the first responder, this should work: [self.view endEditing:YES]

In one of my applications I often want the first responder to resign if the user taps on the background. For this purpose I wrote a category on UIView, which I call on the UIWindow.

The following is based on that and should return the first responder.

@implementation UIView (FindFirstResponder)
- (id)findFirstResponder
{
    if (self.isFirstResponder) {
        return self;        
    }
    for (UIView *subView in self.subviews) {
        id responder = [subView findFirstResponder];
        if (responder) return responder;
    }
    return nil;
}
@end

iOS 7+

- (id)findFirstResponder
{
    if (self.isFirstResponder) {
        return self;
    }
    for (UIView *subView in self.view.subviews) {
        if ([subView isFirstResponder]) {
            return subView;
        }
    }
    return nil;
}

Swift:

extension UIView {
    var firstResponder: UIView? {
        guard !isFirstResponder else { return self }

        for subview in subviews {
            if let firstResponder = subview.firstResponder {
                return firstResponder
            }
        }

        return nil
    }
}

Usage example in Swift:

if let firstResponder = view.window?.firstResponder {
    // do something with `firstResponder`
}

A common way of manipulating the first responder is to use nil targeted actions. This is a way of sending an arbitrary message to the responder chain (starting with the first responder), and continuing down the chain until someone responds to the message (has implemented a method matching the selector).

For the case of dismissing the keyboard, this is the most effective way that will work no matter which window or view is first responder:

[[UIApplication sharedApplication] sendAction:@selector(resignFirstResponder) to:nil from:nil forEvent:nil];

This should be more effective than even [self.view.window endEditing:YES].

(Thanks to BigZaphod for reminding me of the concept)

Here's a category that allows you to quickly find the first responder by calling [UIResponder currentFirstResponder]. Just add the following two files to your project:

UIResponder+FirstResponder.h

#import <Cocoa/Cocoa.h>
@interface UIResponder (FirstResponder)
    +(id)currentFirstResponder;
@end

UIResponder+FirstResponder.m

#import "UIResponder+FirstResponder.h"
static __weak id currentFirstResponder;
@implementation UIResponder (FirstResponder)
    +(id)currentFirstResponder {
         currentFirstResponder = nil;
         [[UIApplication sharedApplication] sendAction:@selector(findFirstResponder:) to:nil from:nil forEvent:nil];
         return currentFirstResponder;
    }
    -(void)findFirstResponder:(id)sender {
        currentFirstResponder = self;
    }
@end

The trick here is that sending an action to nil sends it to the first responder.

(I originally published this answer here: https://stackoverflow.com/a/14135456/322427)