NavigationBarBackgroundHider

Helper to easily hide the navigation bar background on scrolling

What?

Sometimes, you want to hide the background of a navigation bar until the user scrolls to a specific point. For example, you might have a header image that you want to be unobscured by the blur, until the user scrolls past it. This small library makes that easily possible.

How?

In your view controller, call enableNavigationBarBackgroundHiding() to make navigation bar hiding active:

override func viewDidLoad() {
	// this will hide the navigation bar's background until
	// the user scrolls to the first section of the tableview
	enableNavigationBarBackgroundHiding()
}

If you don't have a `UITableView, you can provide your own offset provider that tells the bar hider when to hide/show the bar: just return the point where the bar should become visible:

override func viewDidLoad() {
	// this will make the bar's background visible when the scroll view contentOffset > 100 or 200 
	// depending on some variable. You can put any logic here, just make sure to
	// not retain `self` strongly, otherwise you have a retain cycle.
	enableNavigationBarBackgroundHiding() { [weak self] scrollView in 
		return self?.someVariable == true ? 100 : 200
	}
}

Usage

In your UIViewController subclass, you can optionally override the following:

• override navigationBarHidingStyle to provide one of the default bar hiding styles. (e.g. return .alwaysHidden to always hide the bar)
• override mainContentScrollViewForNavigationBarHiding to return the UIScrollView to use

To enable bar hiding, call: - enableNavigationBarBackgroundHiding() - or, by specifying the scroll view to use directly: enableNavigationBarBackgroundHiding(with: someScrollView)

You can also pass an offset provider callback, used to determine when to show/hide the bar:

enableNavigationBarBackgroundHiding(with: someScrollView) {
	return scrollView in return scrollView.contentSize.height * 0.5
}

To disable bar hiding, call: - disableNavigationbarBackgroundHiding()

To get the active bar hider, call: - self.navigationBarBackgroundHider in your view controller

Customizing

The bar hider has a lot of customization points. First, call navigationBarBackgroundHider to get the current bar hider after enabling it.

• isShowingBackground you can query this property to see if the background is visible

• update(animated:) you can call this to do an immediate update of the background's visibility

• addAdditionalCallback() you can register extra callbacks that will be called when the background's visibility is toggled

• updateHandler you can optionally set your own handler that gets called to update the navigation bar background.

• makeNavigationBarBackgroundTransparentHandler you can optionally set the handler that gets called to make the bar's background transparent.

• makeNavigationBarBackgroundVisibleHandler you can optionally set the handler that gets called to make the bar's background visible.

• offsetForHidingProvider you can set a handler that determines when the bar's background will be hidden when the specified scroll view is scrolled.

All handlers have default implementations.The default implementations are also accessible and can be called directly. You can use this to override some behaviour dynamically: - defaultUpdateHandler (calls makeNavigationBarBackgroundTransparentHandler and makeNavigationBarBackgroundVisibleHandler) when needed) - defaultMakeBackgroundTransparentHandler (calls UINavigationItem.makeNavigationBarBackgroundTransparent()) - defaultMakeBackgroundVisibleHandler (calls UINavigationItem.makeNavigationBarBackgroundVisible()) - defaultOffsetForHidingProvider (returns the offset of the first section for UITableView, otherwise 0)