Question

Lets say that I have 4 view controllers (call them FirstView,SecondView,ThirdView,FourthView) which are created programmatically and all are in separate files:

In AppDelegate.m didFinishLaunchingWithOptions method I have these lines of code

self.rootViewController = [[rootViewController alloc]initWithNibName:@"rootViewController" bundle:nil];
self.window.rootViewController = self.rootViewController;

In rootViewController.m loadview method I have

self.view = [[UIView alloc]initWithFrame:[UIScreen mainScreen].applicationFrame];
self.firstView = [[FirstView alloc]init];
[self.view addSubview:self.firstView.view]; 

That code works fine – first view is displayed.

Let’s continue

In FirstView.m switchViews method

NOTE: Please see the comments in code

 self.secondView = [[SecondView alloc] initWithNibName:@"SecondView" bundle:nil];


// I think here secondView is added to rootViewController - right ?
[self.view.superview addSubview:self.secondView.view];

// Here first view is removed from rootViewController - right ?
[self.view removeFromSuperview];

Here is how I add/remove views.

Is this approach correct?
Can you recommend a better solution?

I have read about UINavigationController, but I don’t think it could be a solution in this case.

Answer 1

You say:

I have 4 views (call them FirstView …

Then you say:

[self.view addSubview:self.firstView.view]; 

Which makes me think that FirstView isn’t actually a UIView – as you claim it is. Instead, it’s probably a UIViewController – a different beast altogether.

If my suspicion is correct – then you are “off-track” so to speak.

Going beyond that to your sample code snippet:

self.secondView = [[SecondView alloc] initWithNibName:@"SecondView" bundle:nil];

// I think here secondView is added to rootViewController - right ?
[self.view.superview addSubview:self.secondView.view];

// Here first view is removed from rootViewController - right ?
[self.view removeFromSuperview];

This is definitely not a great idea. Here’s why:

First: your view controller doesn’t explicitly “know” anything about the superview you are so casually inserting and removing subviews to/from – so it shouldn’t do that. You may, alternatively, create your own view and insert/remove subviews from that – which would not only be perfectly acceptable but also common practice.

Second: if these are actually UIViewControllers like I think they are – then you are not properly handling hooking them up to the UIViewController event chain – which means methods on these subclasses like viewDidAppear: or viewDidUnload will not fire.