Drop in replacement for UITabBarController that plays well with UINavigationController as parent

DRTabBarController.h

//
// Created by Dan Rosenstark on 2/28/15.
// Copyright (c) 2015 Confusion Studios LLC. All rights reserved.
//
#import <UIKit/UIKit.h>

@interface DRTabBarController : UIViewController <UITabBarDelegate>;

@property (nonatomic, strong) NSArray *viewControllers;
@property (nonatomic, strong) UITabBar *tabBar;
@property (nonatomic, strong) UIView *mainView;

@end

DRTabBarController.m

//
// Created by dr2050 on 2/28/15.
// Copyright (c) 2015 Confusion Studios LLC. All rights reserved.
//
#import "DRTabBarController.h"

@implementation DRTabBarController

- (instancetype)init {
    self = [super init];
    if (self) {
        self.tabBar = [[UITabBar alloc] init];
        self.tabBar.delegate = self;
        self.mainView = [[UIView alloc] init];
    }
    return self;
}

- (void)viewDidLoad {
    [self.view addSubview:self.tabBar];
    [self.view addSubview:self.mainView];
}

- (void)setViewControllers:(NSArray *)viewControllers {
    _viewControllers = viewControllers;

    NSMutableArray *tabBarItems = [NSMutableArray array];
    for (UIViewController *controller in viewControllers) {
        UITabBarItem *item = controller.tabBarItem;
        [tabBarItems addObject:item];
    }
    self.tabBar.items = tabBarItems;
}

- (void)viewWillAppear:(BOOL)animated {
    [self.tabBar setSelectedItem:self.tabBar.items.firstObject];
    [self tabBar:self.tabBar didSelectItem:self.tabBar.items.firstObject];
}

-(void)viewDidLayoutSubviews {
    CGRect frame = self.view.bounds;
    UITabBarController *throwaway = [[UITabBarController alloc] init];
    frame.size.height = throwaway.tabBar.frame.size.height;
    frame.origin.y = self.view.bounds.size.height - frame.size.height;
    self.tabBar.frame = frame;
    self.tabBar.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleTopMargin;
    
    frame = self.view.bounds;
    frame.size.height -= self.tabBar.frame.size.height;
    
    float navbarHeight = self.navigationController.navigationBar.frame.size.height;
    // WARNING: MAGIC NUMBER FOR STATUS BAR HEIGHT!
    // cannot use UIApplication.sharedApplication.statusBarFrame.size.height because
    // reports are not right with in-call status bar
    float statusBarHeight = UIApplication.sharedApplication.statusBarHidden ? 0 : 20;
    float topBarHeight = navbarHeight + statusBarHeight;

    frame.origin.y += topBarHeight;
    frame.size.height -= topBarHeight;
    self.mainView.frame = frame;
    self.mainView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
}

- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item {
    NSUInteger index = [self.tabBar.items indexOfObject:item];
    UIView *view = [[self.viewControllers objectAtIndex:index] view];
    view.frame = self.mainView.bounds;
    view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [self.mainView addSubview:view];
    [self.mainView bringSubviewToFront:view];
}
@end

The magic variable, 20, is used instead of status bar height because the in-call status bar messes things up.