Init based Storyboard View Controller Instantiation

Models.swift

import Foundation

// Some clearly non-NSObject-based models:

enum Coconut: String {
    case small, medium, large
}

struct Tomato {
    static var red = Tomato(color: #colorLiteral(red: 0.7490196078, green: 0.09803921569, blue: 0.02352941176, alpha: 1))
    static var green = Tomato(color: #colorLiteral(red: 0.4028071761, green: 0.7315050364, blue: 0.2071235478, alpha: 1))
    static var yellow = Tomato(color: #colorLiteral(red: 0.9346159697, green: 0.6284804344, blue: 0.1077284366, alpha: 1))

    let color: UIColor
    init(color: UIColor) {
        self.color = color
    }
}

struct Banana {
    let coconut: Coconut?
    let tomato: Tomato
}

// MARK: - Coding
// We have to create our own protocol so structs and enums can use it too
protocol Coding {
    init?(coder: NSCoder)
    func encode(coder: NSCoder)
}

extension Tomato: Coding {
    init?(coder: NSCoder) {
        guard let color = coder.decodeAdhocObject(forKey: "color") as? UIColor else {
            return nil
        }
        self.color = color
    }

    func encode(coder: NSCoder) {
        coder.encodeAdhocObject(color, forKey: "color")
    }
}

extension Coconut: Coding {
    init?(coder: NSCoder) {
        guard let size = coder.decodeAdhocObject(forKey: "size") as? String else {
            return nil
        }
        self.init(rawValue: size)
    }

    func encode(coder: NSCoder) {
        coder.encodeAdhocObject(rawValue, forKey: "size")
    }
}

extension Banana: Coding {
    init?(coder: NSCoder) {
        guard let tomato = Tomato(coder: coder) else {
            return nil
        }
        self.tomato = tomato
        self.coconut = Coconut(coder: coder)
    }

    func encode(coder: NSCoder) {
        tomato.encode(coder: coder)
        coconut?.encode(coder: coder)
    }
}

SampleViewController.swift

import UIKit

class RootViewController: UIViewController {
    @IBAction func buttonAction(_ sender: AnyObject) {
        // defined in Models.swift
        let banana = Banana(coconut: .medium, tomato: .green)
        let controller = ViewController(banana: banana)
        present(controller, animated: true)
    }
}

class ViewController: StoryboardBackedViewController {
    let banana: Banana

    @IBOutlet weak var label: UILabel!

    init(banana: Banana) {
        self.banana = banana
        super.init(storyboardIdentifier: "ViewController") { coder in
            banana.encode(coder: coder)
        }
    }

    required init?(coder: NSCoder) {
        guard let banana = Banana(coder: coder) else {
            return nil
        }
        self.banana = banana
        super.init(coder: coder)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = banana.tomato.color
        label.text = banana.coconut?.rawValue
    }
}

StoryboardBackedViewController.h

#import <UIKit/UIKit.h>


NS_ASSUME_NONNULL_BEGIN

@interface StoryboardBackedViewController : UIViewController

// This method returns a different instance of self, so properties on self must be set *after* calling this initializer.
- (instancetype)initWithStoryboardIdentifier:(NSString *)identifier configurationBlock:(void(^_Nonnull)(NSCoder *coder))configurationBlock NS_DESIGNATED_INITIALIZER;

- (_Nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;

#pragma mark - Unavailable

- (instancetype)initWithNibName:(NSString * _Nullable)nibNameOrNil bundle:(NSBundle * _Nullable)nibBundleOrNil NS_UNAVAILABLE;

- (instancetype)init NS_UNAVAILABLE;

@end

@interface NSCoder (AdHoc)

- (nullable id)decodeAdhocObjectForKey:(nonnull NSString *)key;
- (void)encodeAdhocObject:(nonnull id)object forKey:(nonnull NSString *)key;

@end

NS_ASSUME_NONNULL_END

StoryboardBackedViewController.m

//
//  StoryboardBackedViewController.m
//  Fabric
//
//  Created by Javier Soto on 9/6/15.
//  Copyright © 2015 Fabric. All rights reserved.
//

#import "StoryboardBasedViewController.h"
#import "Aspects.h"
#import <objc/runtime.h>


@interface UIStoryboard (FABMainStoryboard)

+ (instancetype)fab_mainStoryboard;

@end

@implementation UIStoryboard (FABMainStoryboard)

+ (instancetype)fab_mainStoryboard {
    return [self storyboardWithName:@"Main" bundle:nil];
}

@end

#pragma mark - Privates

@interface UIStoryboard (Privates)
- (nullable UINib *)nibForViewControllerWithIdentifier:(nonnull NSString *)identifier;
@end


@implementation StoryboardBackedViewController

// Instantiating controllers from UIStoryboard is a horrible API that breaks that designated initializer chain.
// Implementing this in Obj-C so that we can inherit from this and compose initializers properly.

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-designated-initializers"

- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    NSAssert(NO, @"Must use -%@", NSStringFromSelector(@selector(initWithStoryboardIdentifier:configurationBlock:)));
    return nil;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    return self;
}

- (instancetype)initWithStoryboardIdentifier:(NSString *)identifier configurationBlock:(void (^ _Nonnull)(NSCoder * _Nonnull))configurationBlock {
    SEL selector = @selector(unarchiverForInstantiatingReturningError:);
    AspectOptions aspectOptions = AspectPositionInstead | AspectOptionAutomaticRemoval;
    [UINib aspect_hookSelector:selector withOptions:aspectOptions usingBlock:^(id<AspectInfo> aspect, NSError **error){
        UINib *nib = aspect.instance;
        NSInvocation *invocation = aspect.originalInvocation;
        NSCoder *coder = nil;
        [invocation invokeWithTarget:nib];
        [invocation getReturnValue:&coder];
        configurationBlock(coder);
        coder = nil;
    } error:nil];

    UIStoryboard *storyboard = [UIStoryboard fab_mainStoryboard];
    UINib *nib = [storyboard nibForViewControllerWithIdentifier:identifier];
    NSDictionary *options = @{ @"UINibExternalObjects": @{ @"UIStoryboardPlaceholder": storyboard } };
    id scene = [[NSClassFromString(@"UIStoryboardScene") alloc] init];
    [nib instantiateWithOwner:scene options:options];

    id controller = [scene performSelector:@selector(sceneViewController)];
    self = controller;
    return self;
}

@end

#pragma clang diagnostic pop

@implementation NSCoder (AdHoc)

- (NSMutableDictionary <NSObject *, NSString *>*)adhoc_storage {
    const void *key = @selector(adhoc_storage);
    NSMutableDictionary *result;
    result = objc_getAssociatedObject(self, key);
    if (!result) {
        result = [NSMutableDictionary dictionary];
        objc_setAssociatedObject(self, key, result, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return result;
}

- (void)encodeAdhocObject:(id)object forKey:(NSString *)key {
    self.adhoc_storage[key] = object;
}

- (id)decodeAdhocObjectForKey:(NSString *)key {
    return self.adhoc_storage[key];
}

@end