AbstractViewController.h

#import <UIKit/UIKit.h>

@interface AbstractViewController : UIViewController

@property (nonatomic, strong) Class specialButtonClass;
@property (nonatomic, strong) IBOutlet UIButton *specialButton; // laid out in nib

@end

AbstractViewController.m

#import "AbstractViewController.h"
#import "UIButton+NLDuplicate.h"

@implementation NLRootViewControllerPad

#pragma mark Object Lifecycle

- (id)init
{
    NSString *nibName = NSStringFromClass(AbstractViewController.class);
    self = [super initWithNibName:nibName
                           bundle:nil];
    return self;
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    return [self init];
}

#pragma mark UIView lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self _updateSpecialButtonWithCustomClass:self.specialButtonClass];
}

- (void)_updateSpecialButtonWithCustomClass:(Class)class
{
    self.specialButton = ([self _swapButton:self.specialButton
                     withDuplicateFromClass:class
                                     inView:self.view]) ?: self.specialButton;
}

- (UIButton *)_swapButton:(UIButton *)button withDuplicateFromClass:(Class)class inView:(UIView *)view
{
    if (class == nil) return nil;

    UIButton *oldButton = button;
    UIButton *newButton = [UIButton nl_duplicateButton:button withClass:class];

    [view addSubview:newButton];
    [oldButton removeFromSuperview];

    return newButton;
}

- (void)setSpecialButtonClass:(Class)specialButtonClass
{
    _specialButtonClass = specialButtonClass;
    [self _updateSpecialButtonWithCustomClass:_specialButtonClass];
}

@end

ConcreteViewController.h

#import <UIKit/UIKit.h>
#import "AbstractViewController.h"

@interface AbstractViewController : AbstractViewController
@end

ConcreteViewController.m

#import "ConcreteViewController.h"

@interface AwesomeButton : UIButton
@end
@implementation AwesomeButton

- (void)drawRect:(CGRect)rect
{
    [super drawRect:rect];
    // custom drawing
}

@end

@implementation ConcreteViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.specialButtonClass = AwesomeButton.class;
}

@end

UIButton+NLDuplicate.h

#import <UIKit/UIKit.h>

@interface UIButton (NLDuplicate)

/**
 * Duplicates the given `UIButton` object (copying its various properties) into
 * a newly initialized button allocated from the given `Class`.
 *
 * @discussion This is really a v0.1 utility method, only duplicating the specific
 *             properties I needed at the time. It has some baseline test coverage
 *             (see UIButton+NLDuplicateTests.m), and might be a good candidate
 *             for generalizing across other UIViews or general NSObjects.
 *
 *             I primary use case is for replacing an Interface Builder initialized
 *             object with one created from a custom class that you want to switch
 *             out at runtime. You would duplicate an object created in the
 *             Interface Builder file, replacing its various outlets and position
 *             in the view hierarchy with the duplicate object.
 */
+ (instancetype)nl_duplicateButton:(UIButton *)button withClass:(Class)class;

@end

UIButton+NLDuplicate.m

#import "UIButton+NLDuplicate.h"

@implementation UIButton (NLDuplicate)

+ (instancetype)nl_duplicateButton:(UIButton *)button withClass:(Class)class
{
    class = class ?: self;
    UIButton *newButton = [class buttonWithType:button.buttonType];

    newButton.frame = button.frame;

    for (id target in [button allTargets]) {
        for (NSString *selectorName in [button actionsForTarget:target forControlEvent:UIControlEventTouchUpInside]) {
            [newButton addTarget:target
                          action:NSSelectorFromString(selectorName)
                forControlEvents:UIControlEventTouchUpInside];
        }
    }

    id<NSFastEnumeration> controlStates = @[
        @(UIControlStateNormal),
        @(UIControlStateSelected),
        @(UIControlStateHighlighted),
        @(UIControlStateHighlighted|UIControlStateSelected)
    ];
    for (NSNumber *controlState in controlStates) {
        UIControlState cs = controlState.unsignedIntegerValue;
        [newButton setImage:[button imageForState:cs]
                   forState:cs];

    }

    return newButton;
}

@end

UIButton+NLDuplicateTests.m

#import <SenTestingKit/SenTestingKit.h>
#import "UIButton+NLDuplicate.h"

@interface SpecialButton : UIButton
@end
@implementation SpecialButton
@end

@interface TestTargetAction : NSObject
@end
@implementation TestTargetAction
- (void)someAction:(id)sender {}
@end

@interface TestImage : UIImage
@end
@implementation TestImage
+ (instancetype)testImage
{
    CGSize size = (CGSize) {1, 1};
    UIGraphicsBeginImageContext(size);

    [UIColor.redColor setFill];
    [[UIBezierPath bezierPathWithRect:CGRectMake(0, 0, size.width, size.height)] fill];

    UIImage *img =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return (id)img;
}
@end

#pragma mark -

@interface UIButton_NLDuplicateTests : SenTestCase
@end

@implementation UIButton_NLDuplicateTests

- (void)testDefaultDuplicateClassToUIBUtton
{
    UIButton *newButton = [UIButton nl_duplicateButton:[UIButton buttonWithType:UIButtonTypeCustom] withClass:nil];
    STAssertTrue([newButton isKindOfClass:UIButton.class], nil);
}

- (void)testEqualButtonTypes
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:nil];
    STAssertEquals(newButton.buttonType, oldButton.buttonType, nil);
}

- (void)testInitializesDuplicateButtonWithGivenClass
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];
    STAssertTrue([newButton isKindOfClass:SpecialButton.class], nil);
}

- (void)testEqualFrames
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    oldButton.frame = CGRectMake(20, 20, 100, 100);
    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];
    STAssertTrue(CGRectEqualToRect(newButton.frame, oldButton.frame), nil);
}

- (void)testDuplicateTargetActionForUIControlEventTouchUpInside
{
    id buttonActionTarget = [TestTargetAction new];
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [oldButton addTarget:buttonActionTarget action:@selector(someAction:) forControlEvents:UIControlEventTouchUpInside];

    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];

    STAssertEqualObjects([newButton actionsForTarget:buttonActionTarget forControlEvent:UIControlEventTouchUpInside],
                         [oldButton actionsForTarget:buttonActionTarget forControlEvent:UIControlEventTouchUpInside],
                         nil);
}

- (void)testImageForUIControlStateNormal
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [oldButton setImage:[TestImage testImage] forState:UIControlStateNormal];

    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];

    STAssertEqualObjects([newButton imageForState:UIControlStateNormal],
                         [oldButton imageForState:UIControlStateNormal],
                         nil);
}

- (void)testImageForUIControlStateSelected
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [oldButton setImage:[TestImage testImage] forState:UIControlStateSelected];

    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];

    STAssertEqualObjects([newButton imageForState:UIControlStateSelected],
                         [oldButton imageForState:UIControlStateSelected],
                         nil);
}

- (void)testImageForUIControlStateHighlighted
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [oldButton setImage:[TestImage testImage] forState:UIControlStateHighlighted];

    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];

    STAssertEqualObjects([newButton imageForState:UIControlStateHighlighted],
                         [oldButton imageForState:UIControlStateHighlighted],
                         nil);
}

- (void)testImageForUIControlStateHighlightedAndSelected
{
    UIButton *oldButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [oldButton setImage:[TestImage testImage] forState:UIControlStateHighlighted|UIControlStateSelected];

    UIButton *newButton = [UIButton nl_duplicateButton:oldButton withClass:SpecialButton.class];

    STAssertEqualObjects([newButton imageForState:UIControlStateHighlighted|UIControlStateSelected],
                         [oldButton imageForState:UIControlStateHighlighted|UIControlStateSelected],
                         nil);
}

@end