Pushing to a new Viewcontroller from an inactive Viewcontroller (programatically)

Question

Short explanation.

I have a ContainerViewController that I'm pushing to the navigationStack.

The ContainerViewController has 2 child ViewControllers. A SlidePanelViewController (a slide-out menu) and a CenterViewController (the content)

I have a button in my menu to "sign Out". When this button is clicked I want to push ContainerViewController (and it's 2 childViewControllers) to my LandingPageViewController.

Here's the function I am trying to call:

func signOut() {
println("signOut")


// Set up the landing page as the main viewcontroller again.
let mainTableViewController = LandingPageVC()
mainTableViewController.navigationItem.setHidesBackButton(true, animated: false)
mainTableViewController.skipView = false
self.navigationController!.pushViewController(mainTableViewController, animated: true)

// Disable menu access
menuEnabled = false

// change status bar style back to default (black)
UIApplication.sharedApplication().statusBarStyle = UIStatusBarStyle.Default
}

At first I tried putting this in my SlidePanelViewController. That didn't work. So I put it where I'm assuming it belongs in the ContainerViewController.

However when I click my signOutButton in my menu. I'm presented with the error:

fatal error: unexpectedly found nil while unwrapping an Optional value

When looking into the error. This is the line causing it:

self.navigationController!.pushViewController(mainTableViewController, animated: true)

After the error I checked that the function works, by adding a UINavigationBarButtonItem that called the function (in my ContainerViewController). It did exactly what I wanted.

However when I call this function from my Menu (again my menu is a childViewController of the ContainerViewController). It does not work.

I'm attempting to call it like so:

ContainerViewController().signOut()

I also tried adding a Delegate to my SidePanelViewController like this:

Before the class:

@objc protocol SidePanelViewControllerDelegate {
    optional func needsSignOut(sender: SidePanelViewController)
    optional func toggleLeftPanel()
    optional func collapseSidePanels()
}

in viewDidLoad():

//  Make sure your delegate is weak because if a ContainerViewController owns
//  a reference to a SidePanelViewController and the container view controller
//  is its delegate, you'll end up with a strong reference cycle!
weak var delegate: SidePanelViewControllerDelegate?

in my tap gesture function:

func signOutTapGesture() {
    println("signOutTapGesture")
    selectView(signOutView)

    delegate?.needsSignOut?(self)
    println(delegate)
}

before my ContainerViewController class:

var leftViewController: SidePanelViewController?

my ContainerViewController class:

class ContainerViewController: UIViewController, CenterViewControllerDelegate, SidePanelViewControllerDelegate, UIGestureRecognizerDelegate {

in my ContainerViewController's viewDidLoad()

leftViewController?.delegate = self

And I changed the signOut function in the ContainerViewController class to this:

func needsSignOut(sender: SidePanelViewController) {
    println("needsSignOut called")
    self.signOut()
}

However using the delegate like above, doesn't seem to do anything either.

Any help as to How I can successfully push my LandingPageVC from the menu would be greatly appreciated! (I'm not using storyboards)

Answer 1

You're attempting to call signOut with ContainerViewController().signOut(). This will create a new ContainerViewController and because you haven't pushed it onto the navigation controller's stack, navigationController is nil. Try just calling self.signOut(). (I'm assuming signOut in a method of ContainerViewController)

Update - delegates

Your delegate property should go in SidePanelViewController. I'll give you and example of how to implement it:

SidePanelViewController: (Note - the protocol doesn't have to go here but I think it keeps things organised)

@objc protocol SidePanelViewControllerDelegate {
    optional func needsSignOut(sender: SidePanelViewController)
}

class SidePanelViewController: UIViewController {
    //  Make sure your delegate is weak because if a ContainerViewController owns
    //  a reference to a SidePanelViewController and the container view controller
    //  is its delegate, you'll end up with a strong reference cycle!
    weak var delegate: SidePanelViewControllerDelegate?

    //  Called when the UIButton is pressed.
    func myButtonWasPressed() {
        delegate?.needsSignOut?(self)
    }
}

ContainerViewController:

class ContainerViewController: UIViewController {
    var sidePanel: SidePanelViewController!
    // Setup the side panel...

    override func viewDidLoad() {
        super.viewDidLoad()
        sidePanel.delegate = self
    }

    func signOut() {
        // Sign out stuff here.
    }
}

//  The ContainerViewController needs to conform to the SidePanelViewControllerDelegate
//  protocol if we want the delegate to work. (This could have gone in the initial
//  class declaration.)
extension ContainerViewController : SidePanelViewControllerDelegate {
    func needsSignOut(sender: SidePanelViewController) {
        self.signOut()
    }
}

Hope that helps.

Answer 2

The problem seems to be that navigationController is nil and you're trying to force unwrap it (as indicated by your error).

One problem I discussed in my other answer.

Another problem may be you haven't added a navigation controller. To do this you need to:

If you're using Storyboards

You need to make sure you've embedded your UINavigationController. After that, when you use navigationController it won't be nil and you'll be able to push your view controller.

When you're on your storyboard:

Also, if you're using storyboards, have you considered using segues to move around instead of calling presentViewController? I've found it makes everything much easier.

If you're not using Storyboards

Have a look at this post: Programatically creating UINavigationController in iOS