NavigationBar delay updating barTintColor iOS10

Question

Context:

Let's say we have one NavigationController and 2 viewControllers. ViewControllerA has a blue navigationBar, while ViewControllerB has a green one.

I set them up like so :

override func viewWillAppear(_ animated: Bool) {
        self.navigationController?.navigationBar.barTintColor = UIColor.blue    // Green if ViewController B
    }

It works well when I got from A to B, but when I return, the navigationBar teint is updated after. Like if it was set up in the viewDidAppear.

Expected:

The navigation bar should have its navigation bar color updated without delay.

Solutions tried:

• I've seen this SO post, and I tried the solution. It worked, but would make the management of the navigation bar a lot more complex and painful. (in a real app)

• I've tried to change the navbar teint in the ViewWillDisappear method. Didn't work.

More:

This is caused by a change on the ios10 API. I've read the release notes, but it's still unclear what should be done in this case.

In iOS 10, UIKit has updated and unified background management for UINavigationBar, UITabBar, and UIToolbar. In particular, changes to background properties of these views (such as background or shadow images, or setting the bar style) may kick off a layout pass for the bar to resolve the new background appearance.

In particular, this means that attempts to change the background appearance of these bars inside of layoutSubviews, -[UIView updateConstraints], viewWillLayoutSubviews, viewDidLayoutSubviews, updateViewConstraints, or any other method that is called in response to layout may result in a layout loop.

In some cases you can break these layout loops by ensuring that you always use the same object instance when objects (such as UIImage or UIColor) are required. But in general you should avoid doing this.

Question:

What would be the best way to handle the navigation bar changes between different navigation controllers in iOS 10 ?

Answer 1

Try this code:

Note: Code Tested in Swift 3.

In ViewController A:

    override var isViewLoaded: Bool {
    title = "View 1"
    navigationController?.navigationBar.barTintColor = .blue
    navigationController?.navigationBar.isTranslucent = true
    navigationController?.navigationBar.tintColor = UIColor.white
    navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName:UIColor.white]
    UIApplication.shared.statusBarStyle = .lightContent
    self.navigationController?.navigationBar.barStyle = .black // In case statusbar Light content wont work.
    return true
    }

In ViewController B:

    override var isViewLoaded: Bool {
    title = "View 2"
    navigationController?.navigationBar.barTintColor = .green
    navigationController?.navigationBar.tintColor = .white
    navigationController?.navigationBar.isTranslucent = true
    navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName:UIColor.white]
    return true
    }

Output: No delay what so ever...

Pattern Image as a TintColor.

In ViewController A:

 navigationController?.navigationBar.barTintColor = UIColor(patternImage: UIImage(named: "viewOneImage.jpg")!)

In ViewController B:

 navigationController?.navigationBar.barTintColor = UIColor(patternImage: UIImage(named: "viewTwoImage.jpg")!)

Output:

Answer 2

I wasn't happy with the solution overriding isViewLoaded because if there's ever a time view_controller_a is shown and you use the value of view_controller_b.isViewLoaded for whatever reason, then you'll end up changing the nav bar to the wrong display.

Instead, I would store the nav bar configuration you want in each view controller and use UINavigationControllerDelegate:

class NavBarConfig
{
    var background_color: UIColor

    init( background_color: UIColor )
    {
        self.background_color = background_color
    }
}

class ViewController: UIViewController
{
    var nav_bar_config: NavBarConfig?
}

class NavControllerDelegate: UINavigationControllerDelegate
{
    //Called just before the navigation controller displays a view controller’s view and navigation item properties.
    func navigationController( _ nav_controller: UINavigationController, willShow view_controller: UIViewController, animated: Bool )
    {
        if let view_controller = view_controller as? ViewController, let nar_bar_config = view_controller.nav_bar_config
        {
            nav_controller.navigationBar.barTintColor = view_controller.nar_bar_config.background_color
        }
    }
}

After setting the delegate on your nav controller, your_nav_controller.delegate = NavControllerDelegate(), the delegate method will be called just before each view controller is displayed allowing you to configure the nav bar how you wish.