Chaining VCs from ViewModels

ViewModelServices.m

- (void)pushViewModel:(BaseViewModel *)nextViewModel
{
	NSString *from = [self standardNameFromViewModel:_currentViewController.viewModel];
	NSString *to = [self standardNameFromViewModel:nextViewModel];

	// We are going to try and find a segue to go to the next viewModel. The way segues are named
	// in our storyboard should be: FromModel::ToModel
	// 1. try Segue method. For example, a segue going from WelcomeViewController to LoginViewController would be named "Welcome::Login"
	// 2. If a segue is not found, try to instantiate the view controller and push it directly. We look up the view controller by its stripped model name (i.e. "WelcomeViewModel" -> "Welcome")
	// 3. If the view controller is not found in the storyboard, try a XIB with the stripped model name.
	@try
	{
		// Hook into currentViewController's -prepareForSegue method to automatically bind view model to instantiated view controller
		UIViewController *currentVC = (UIViewController *)_currentViewController;
		if (currentVC)
		{
			// this Aspect hook will execute ONCE on the target view controller and bind the view model
			// to the UIViewController that was instantiated from a segue
			[currentVC aspect_hookSelector:@selector(prepareForSegue:sender:)
											withOptions:AspectPositionAfter | AspectOptionAutomaticRemoval
											 usingBlock:^(id<AspectInfo> ai, UIStoryboardSegue *segue, id sender) {
												 LOG_MODEL(0, @"prepareForSegue from %@ to %@", segue.sourceViewController, segue.destinationViewController);
												 id viewController = segue.destinationViewController;
												 if ([viewController isKindOfClass:[MainTabBarViewController class]])
														[self configureTabBarController:(MainTabBarViewController *) viewController withViewModel:nextViewModel];
													else
														[self configureNextController:(BaseViewController *) viewController withViewModel:nextViewModel];
											 } error:NULL];
		}

		[currentVC performSegueWithIdentifier:[NSString stringWithFormat:@"%@::%@", from, to] sender:self];
	}
	@catch (NSException *exception)
	{
		// Segue not found, try locating the view controller in the storyboard
		UIViewController *viewController = [self.mainStoryboard instantiateViewControllerWithIdentifier:to];
		if (viewController == nil)
			viewController = [[UIViewController alloc] initWithNibName:to bundle:nil];

		if ([viewController isKindOfClass:[MainTabBarViewController class]])
			[self configureTabBarController:(MainTabBarViewController *) viewController withViewModel:nextViewModel];
		else
			[self configureNextController:(id<AppViewController>)viewController withViewModel:nextViewModel];

		// Since there is no segue, we will push from current navigation controller
		[((UIViewController *)_currentViewController).navigationController pushViewController:viewController animated:YES];
	}
}

This code uses the Aspects library by Peter Steinberger https://github.com/steipete/Aspects to automatically configure storyboard segues in MVVM applications when transitioning from one view controller to the other.

To identify the proper segue, we use the source and destination view controller classes and derive a standard format name for the segue. For example, transitioning from a LoginViewController to a MainViewController would look up a segue named "Login::Main" then automagically configure and run it.