UITextField category that let's "next text fields" be assigned via interface builder.

UITextField+Tabbable.m

#import <UIKit/UIKit.h>
#import <objc/runtime.h>

/**
 Adds a property called "nextTextField" to the UITextField class.
 This property can be assigned in IB in a very natural way.
 
 To make this work, something like this should be added to the VC
 that is delegate of the UITextFields:
 
 - (BOOL)textFieldShouldReturn:(UITextField *)textField
 {
    UITextField *next = [textField nextTextField];
    if (next) {
        [next becomeFirstResponder];
    }
    else {
        // do something...
    }
 
    return NO;
 }
 
 This class uses objc_getAssociatedObject and objc_setAssociatedObject.
 More information on objc_getAssociatedObject here:
 https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocAssociativeReferences.html#//apple_ref/doc/uid/TP30001163-CH24-SW1
 */

@interface UITextField (Tabbable)

@property(strong, nonatomic) IBOutlet UITextField *nextTextField;

@end

// This is used
static char associationKey;

@implementation UITextField (Tabbable)

- (UITextField*) nextTextField {
    return objc_getAssociatedObject(self, &associationKey);
}

- (void) setNextTextField:(UITextField *)nextTextField{
    objc_setAssociatedObject(self, &associationKey, nextTextField, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end