ios - How to hide the home indicator with SwiftUI?

Question

What's the UIKit equivalent of the prefersHomeIndicatorAutoHidden property in SwiftUI?

Answer 1

Since I could't find this in the default API either, I made it myself in a subclass of UIHostingController.

What I wanted:

var body: some View {
    Text("I hide my home indicator")
        .prefersHomeIndicatorAutoHidden(true)
}

Since the prefersHomeIndicatorAutoHidden is a property on UIViewController we can override that in UIHostingController but we need to get the prefersHomeIndicatorAutoHidden setting up the view hierarchy, from our view that we set it on to the rootView in UIHostingController.

The way that we do that in SwiftUI is PreferenceKeys. There is lots of good explanation on that online.

So what we need is a PreferenceKey to send the value up to the UIHostingController:

struct PrefersHomeIndicatorAutoHiddenPreferenceKey: PreferenceKey {
    typealias Value = Bool

    static var defaultValue: Value = false

    static func reduce(value: inout Value, nextValue: () -> Value) {
        value = nextValue() || value
    }
}

extension View {
    // Controls the application's preferred home indicator auto-hiding when this view is shown.
    func prefersHomeIndicatorAutoHidden(_ value: Bool) -> some View {
        preference(key: PrefersHomeIndicatorAutoHiddenPreferenceKey.self, value: value)
    }
}

Now if we add .prefersHomeIndicatorAutoHidden(true) on a View it sends the PrefersHomeIndicatorAutoHiddenPreferenceKey up the view hierarchy. To catch that in the hosting controller I made a subclass that wraps the rootView to listen to the preference change, then update the UIViewController.prefersHomeIndicatorAutoHidden:

// Not sure if it's bad that I cast to AnyView but I don't know how to do this with generics
class PreferenceUIHostingController: UIHostingController<AnyView> {
    init<V: View>(wrappedView: V) {
        let box = Box()
        super.init(rootView: AnyView(wrappedView
            .onPreferenceChange(PrefersHomeIndicatorAutoHiddenPreferenceKey.self) {
                box.value?._prefersHomeIndicatorAutoHidden = $0
            }
        ))
        box.value = self
    }

    @objc required dynamic init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    private class Box {
        weak var value: PreferenceUIHostingController?
        init() {}
    }

    // MARK: Prefers Home Indicator Auto Hidden

    private var _prefersHomeIndicatorAutoHidden = false {
        didSet { setNeedsUpdateOfHomeIndicatorAutoHidden() }
    }
    override var prefersHomeIndicatorAutoHidden: Bool {
        _prefersHomeIndicatorAutoHidden
    }
}

Full example that doesn't expose the PreferenceKey type and has preferredScreenEdgesDeferringSystemGestures too on git: https://gist.github.com/Amzd/01e1f69ecbc4c82c8586dcd292b1d30d