Customise top bar with base controller

TopBarViewController

@interface TopBarViewController ()
@property (nonatomic, strong) UIView *statusbarBgView;
@end

@implementation TopBarViewController

- (void)viewDidLoad
{
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  
  if (OS_PRIOR_IOS_7 && ![UIApplication sharedApplication].statusBarHidden) {
    CGFloat statusBarH = [UIApplication sharedApplication].statusBarFrame.size.height;
    CGRect f = (CGRect){0.f, 0.f, self.view.frame.size.width, statusBarH};
    self.statusbarBgView = [[UIView alloc] initWithFrame:f];
    self.statusbarBgView.autoresizingMask = UIViewAutoresizingFlexibleWidth;
    self.statusbarBgView.backgroundColor = [UIColor clearColor];
    [self.view addSubview:self.statusbarBgView];
  }
}

- (void)setBodyView:(UIView *)bodyView
{
  [_bodyView removeFromSuperview];
  
  _bodyView = bodyView;
  [self.view addSubview:_bodyView];
  if (self.topBar) {
    [self.view bringSubviewToFront:self.topBar];
    [self.view bringSubviewToFront:self.statusbarBgView];
  }
  [self layoutBodyViewToFit];
}

- (void)setTopBar:(UIView *)topBar
{
  [_topBar removeFromSuperview];
  _topBar = topBar;
  
  if (OS_PRIOR_IOS_7) {
    CGFloat statusBarH = [UIApplication sharedApplication].statusBarFrame.size.height;
    [_topBar app_setOrigY:statusBarH];
    self.statusbarBgView.backgroundColor = _topBar.backgroundColor;
  }
  
  [self.view addSubview:_topBar];
  [self layoutBodyViewToFit];
}

- (void)setTopBarTranslucent:(BOOL)topBarTranslucent
{
  _topBarTranslucent = topBarTranslucent;
  [self layoutBodyViewToFit];
}

- (void)layoutBodyViewToFit
{
  if (self.bodyView) {
    CGRect rect = self.view.bounds;
    if (!self.topBarHidden && !self.topBarTranslucent && _topBar) {
      rect.origin.y = CGRectGetMaxY(_topBar.frame);
    }
    rect.size.height -= rect.origin.y;
    self.bodyView.frame = rect;
    self.bodyView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
  }
}

@end