Add SwiftUI proof of concept in Maps-SwiftUI example (#481)

Partially solves #281. This adds a new example app which mimics the Maps.app, written in SwiftUI. The code works for iOS 13+, however:
* the project has been created with Xcode 13
* the project uses the SwiftUI lifecycle (iOS 14+)

The source code in Examples/Maps-SwiftUI/Maps/FloatingPanel is ready to move into the library, but there is an issue on SwiftUI’s environment propagation into FloatingPanel. SwiftUI’s environment is propagated to all subviews. However FloatingPanel is not a subview, but a new view controller in the screen (and not a child view controller).

It’s possible to lead behaviors unexpected by SwiftUI users so that this is merged as a sample code until it will be resolved.

Examples/Maps-SwiftUI/Maps/ContentView.swift

@@ -0,0 +1,33 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import SwiftUI
+import MapKit
+
+struct ContentView: View {
+    @State private var region = MKCoordinateRegion(
+        center: CLLocationCoordinate2D(latitude: 37.623198015869235, longitude: -122.43066818432008),
+        span: MKCoordinateSpan(latitudeDelta: 0.4425100023575723, longitudeDelta: 0.28543697435880233)
+    )
+
+    var body: some View {
+        ZStack {
+            Map(coordinateRegion: $region)
+                .ignoresSafeArea()
+            statusBarBlur
+        }
+    }
+
+    private var statusBarBlur: some View {
+        GeometryReader { geometry in
+            VisualEffectBlur()
+                .frame(height: geometry.safeAreaInsets.top)
+                .ignoresSafeArea()
+        }
+    }
+}
+
+struct ContentView_Previews: PreviewProvider {
+    static var previews: some View {
+        ContentView()
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/FloatingPanelView.swift

@@ -0,0 +1,121 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import FloatingPanel
+import SwiftUI
+
+/// A proxy for exposing the methods of the floating panel controller.
+public struct FloatingPanelProxy {
+    /// The associated floating panel controller.
+    public weak var fpc: FloatingPanelController?
+
+    /// Tracks the specified scroll view to correspond with the scroll.
+    ///
+    /// - Parameter scrollView: Specify a scroll view to continuously and
+    ///   seamlessly work in concert with interactions of the surface view.
+    public func track(scrollView: UIScrollView) {
+        fpc?.track(scrollView: scrollView)
+    }
+
+    /// Moves the floating panel to the specified position.
+    ///
+    /// - Parameters:
+    ///   - floatingPanelState: The state to move to.
+    ///   - animated: `true` to animate the transition to the new state; `false`
+    ///     otherwise.
+    public func move(
+        to floatingPanelState: FloatingPanelState,
+        animated: Bool,
+        completion: (() -> Void)? = nil
+    ) {
+        fpc?.move(to: floatingPanelState, animated: animated, completion: completion)
+    }
+}
+
+/// A view with an associated floating panel.
+struct FloatingPanelView<Content: View, FloatingPanelContent: View>: UIViewControllerRepresentable {
+    /// A type that conforms to the `FloatingPanelControllerDelegate` protocol.
+    var delegate: FloatingPanelControllerDelegate?
+
+    /// The behavior for determining the adjusted content offsets.
+    @Environment(\.contentInsetAdjustmentBehavior) var contentInsetAdjustmentBehavior
+
+    /// Constants that define how a panel content fills in the surface.
+    @Environment(\.contentMode) var contentMode
+
+    /// The floating panel grabber handle offset.
+    @Environment(\.grabberHandlePadding) var grabberHandlePadding
+
+    /// The floating panel `surfaceView` appearance.
+    @Environment(\.surfaceAppearance) var surfaceAppearance
+
+    /// The view builder that creates the floating panel parent view content.
+    @ViewBuilder var content: Content
+
+    /// The view builder that creates the floating panel content.
+    @ViewBuilder var floatingPanelContent: (FloatingPanelProxy) -> FloatingPanelContent
+
+    public func makeUIViewController(context: Context) -> UIHostingController<Content> {
+        let hostingController = UIHostingController(rootView: content)
+        hostingController.view.backgroundColor = nil
+        // We need to wait for the current runloop cycle to complete before our
+        // view is actually added (into the view hierarchy), otherwise the
+        // environment is not ready yet.
+        DispatchQueue.main.async {
+            context.coordinator.setupFloatingPanel(hostingController)
+        }
+        return hostingController
+    }
+
+    public func updateUIViewController(
+        _ uiViewController: UIHostingController<Content>,
+        context: Context
+    ) {
+        context.coordinator.updateIfNeeded()
+    }
+
+    public func makeCoordinator() -> Coordinator {
+        Coordinator(parent: self)
+    }
+
+    /// `FloatingPanelView` coordinator.
+    ///
+    /// Responsible to setup the view hierarchy and floating panel.
+    final class Coordinator {
+        private let parent: FloatingPanelView<Content, FloatingPanelContent>
+        private lazy var fpc = FloatingPanelController()
+
+        init(parent: FloatingPanelView<Content, FloatingPanelContent>) {
+            self.parent = parent
+        }
+
+        func setupFloatingPanel(_ parentViewController: UIViewController) {
+            updateIfNeeded()
+            let panelContent = parent.floatingPanelContent(FloatingPanelProxy(fpc: fpc))
+            let hostingViewController = UIHostingController(
+                rootView: panelContent,
+                ignoresKeyboard: true
+            )
+            hostingViewController.view.backgroundColor = nil
+            fpc.set(contentViewController: hostingViewController)
+            fpc.addPanel(toParent: parentViewController, at: 1, animated: false)
+        }
+
+        func updateIfNeeded() {
+            if fpc.contentInsetAdjustmentBehavior != parent.contentInsetAdjustmentBehavior {
+                fpc.contentInsetAdjustmentBehavior = parent.contentInsetAdjustmentBehavior
+            }
+            if fpc.contentMode != parent.contentMode {
+                fpc.contentMode = parent.contentMode
+            }
+            if fpc.delegate !== parent.delegate {
+                fpc.delegate = parent.delegate
+            }
+            if fpc.surfaceView.grabberHandlePadding != parent.grabberHandlePadding {
+                fpc.surfaceView.grabberHandlePadding = parent.grabberHandlePadding
+            }
+            if fpc.surfaceView.appearance != parent.surfaceAppearance {
+                fpc.surfaceView.appearance = parent.surfaceAppearance
+            }
+        }
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/UIHostingController+ignoreKeyboard.swift

@@ -0,0 +1,44 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import SwiftUI
+
+/// This extension makes sure SwiftUI views are not affected by iOS keyboard.
+///
+/// Credits to https://steipete.me/posts/disabling-keyboard-avoidance-in-swiftui-uihostingcontroller/
+extension UIHostingController {
+    public convenience init(rootView: Content, ignoresKeyboard: Bool) {
+        self.init(rootView: rootView)
+
+        if ignoresKeyboard {
+            guard let viewClass = object_getClass(view) else { return }
+
+            let viewSubclassName = String(
+                cString: class_getName(viewClass)
+            ).appending("_IgnoresKeyboard")
+
+            if let viewSubclass = NSClassFromString(viewSubclassName) {
+                object_setClass(view, viewSubclass)
+            } else {
+                guard
+                    let viewClassNameUtf8 = (viewSubclassName as NSString).utf8String,
+                    let viewSubclass = objc_allocateClassPair(viewClass, viewClassNameUtf8, 0)
+                else { return }
+
+                if let method = class_getInstanceMethod(
+                    viewClass,
+                    NSSelectorFromString("keyboardWillShowWithNotification:")
+                ) {
+                    let keyboardWillShow: @convention(block) (AnyObject, AnyObject) -> Void = { _, _ in }
+                    class_addMethod(
+                        viewSubclass,
+                        NSSelectorFromString("keyboardWillShowWithNotification:"),
+                        imp_implementationWithBlock(keyboardWillShow),
+                        method_getTypeEncoding(method)
+                    )
+                }
+                objc_registerClassPair(viewSubclass)
+                object_setClass(view, viewSubclass)
+            }
+        }
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/View+floatingPanel.swift

@@ -0,0 +1,31 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import FloatingPanel
+import SwiftUI
+
+extension View {
+    /// Presents a floating panel using the given closure as its content.
+    ///
+    /// The modifier's content view builder receives a `FloatingPanelProxy`
+    /// instance; you use the proxy's methods to interact with the associated
+    /// `FloatingPanelController`.
+    ///
+    /// - Parameters:
+    ///   - delegate: A type that conforms to the
+    ///     `FloatingPanelControllerDelegate` protocol. You have comprehensive
+    ///     control over the floating panel behavior when you use a delegate.
+    ///   - floatingPanelContent: The floating panel content. This view builder
+    ///     receives a `FloatingPanelProxy` instance that you use to interact
+    ///     with the `FloatingPanelController`.
+    public func floatingPanel<FloatingPanelContent: View>(
+        delegate: FloatingPanelControllerDelegate? = nil,
+        @ViewBuilder _ floatingPanelContent: @escaping (_: FloatingPanelProxy) -> FloatingPanelContent
+    ) -> some View {
+        FloatingPanelView(
+            delegate: delegate,
+            content: { self },
+            floatingPanelContent: floatingPanelContent
+        )
+        .ignoresSafeArea()
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/View+floatingPanelContentInsetAdjustmentBehavior.swift

@@ -0,0 +1,38 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import FloatingPanel
+import SwiftUI
+
+struct ContentInsetKey: EnvironmentKey {
+    static var defaultValue: FloatingPanelController.ContentInsetAdjustmentBehavior = .always
+}
+
+extension EnvironmentValues {
+    /// The behavior for determining the adjusted content offsets.
+    var contentInsetAdjustmentBehavior: FloatingPanelController.ContentInsetAdjustmentBehavior {
+        get { self[ContentInsetKey.self] }
+        set { self[ContentInsetKey.self] = newValue }
+    }
+}
+
+extension View {
+    /// Sets the content inset adjustment behavior for floating panels within
+    /// this view.
+    ///
+    /// Use this modifier to set a specific content inset adjustment behavior
+    /// for floating panel instances within a view:
+    ///
+    ///     MainView()
+    ///         .floatingPanel { _ in
+    ///             FloatingPanelContent()
+    ///         }
+    ///         .floatingPanelContentInsetAdjustmentBehavior(.never)
+    ///
+    /// - Parameter contentInsetAdjustmentBehavior: The content inset adjustment
+    ///   behavior to set.
+    public func floatingPanelContentInsetAdjustmentBehavior(
+        _ contentInsetAdjustmentBehavior: FloatingPanelController.ContentInsetAdjustmentBehavior
+    ) -> some View {
+        environment(\.contentInsetAdjustmentBehavior, contentInsetAdjustmentBehavior)
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/View+floatingPanelContentMode.swift

@@ -0,0 +1,37 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import FloatingPanel
+import SwiftUI
+
+struct ContentModeKey: EnvironmentKey {
+    static var defaultValue: FloatingPanelController.ContentMode = .static
+}
+
+extension EnvironmentValues {
+    /// Used to determine how the floating panel controller lays out the content
+    /// view when the surface position changes.
+    var contentMode: FloatingPanelController.ContentMode {
+        get { self[ContentModeKey.self] }
+        set { self[ContentModeKey.self] = newValue }
+    }
+}
+
+extension View {
+    /// Sets the content mode for floating panels within this view.
+    ///
+    /// Use this modifier to set a specific content mode for floating panel
+    /// instances within a view:
+    ///
+    ///     MainView()
+    ///         .floatingPanel { _ in
+    ///             FloatingPanelContent()
+    ///         }
+    ///         .floatingPanelContentMode(.static)
+    ///
+    /// - Parameter contentMode: The content mode to set.
+    public func floatingPanelContentMode(
+        _ contentMode: FloatingPanelController.ContentMode
+    ) -> some View {
+        environment(\.contentMode, contentMode)
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/View+floatingPanelGrabberHandlePadding.swift

@@ -0,0 +1,36 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import FloatingPanel
+import SwiftUI
+
+struct GrabberHandlePaddingKey: EnvironmentKey {
+    static var defaultValue: CGFloat = 6.0
+}
+
+extension EnvironmentValues {
+    /// The offset of the grabber handle from the interactive edge.
+    var grabberHandlePadding: CGFloat {
+        get { self[GrabberHandlePaddingKey.self] }
+        set { self[GrabberHandlePaddingKey.self] = newValue }
+    }
+}
+
+extension View {
+    /// Sets the grabber handle padding for floating panels within this view.
+    ///
+    /// Use this modifier to set a specific padding to floating panel instances
+    /// within a view:
+    ///
+    ///     MainView()
+    ///         .floatingPanel { _ in
+    ///             FloatingPanelContent()
+    ///         }
+    ///         .floatingPanelGrabberHandlePadding(16)
+    ///
+    /// - Parameter padding: The grabber handle padding to set.
+    public func floatingPanelGrabberHandlePadding(
+        _ padding: CGFloat
+    ) -> some View {
+        environment(\.grabberHandlePadding, padding)
+    }
+}

Examples/Maps-SwiftUI/Maps/FloatingPanel/View+floatingPanelSurfaceAppearance.swift

@@ -0,0 +1,44 @@
+// Copyright 2021 the FloatingPanel authors. All rights reserved. MIT license.
+
+import FloatingPanel
+import SwiftUI
+
+struct SurfaceAppearanceKey: EnvironmentKey {
+    static var defaultValue = SurfaceAppearance()
+}
+
+extension EnvironmentValues {
+    /// The appearance of a surface view.
+    var surfaceAppearance: SurfaceAppearance {
+        get { self[SurfaceAppearanceKey.self] }
+        set { self[SurfaceAppearanceKey.self] = newValue }
+    }
+}
+
+extension View {
+    /// Sets the surface appearance for floating panels within this view.
+    ///
+    /// Use this modifier to set a specific surface appearance for floating
+    /// panel instances within a view:
+    ///
+    ///     MainView()
+    ///         .floatingPanel { _ in
+    ///             FloatingPanelContent()
+    ///         }
+    ///         .floatingPanelSurfaceAppearance(.transparent)
+    ///
+    ///     extension SurfaceAppearance {
+    ///         static var transparent: SurfaceAppearance {
+    ///             let appearance = SurfaceAppearance()
+    ///             appearance.backgroundColor = .clear
+    ///             return appearance
+    ///         }
+    ///     }
+    ///
+    /// - Parameter surfaceAppearance: The surface appearance to set.
+    public func floatingPanelSurfaceAppearance(
+        _ surfaceAppearance: SurfaceAppearance
+    ) -> some View {
+        environment(\.surfaceAppearance, surfaceAppearance)
+    }
+}