Enable to define and use a subclass object of BackdropView (#617)

* Enable to create a subclass of BackdropView
* Add a custom backdrop sample in the Samples example

Examples/Samples/Sources/UseCases/UseCase.swift

@@ -24,6 +24,7 @@ enum UseCase: Int, CaseIterable {
     case showAdaptivePanel
     case showAdaptivePanelWithCustomGuide
     case showCustomStatePanel
+    case showCustomBackdrop
 }
 
 extension UseCase {
@@ -50,6 +51,7 @@ extension UseCase {
         case .showAdaptivePanel: return "Show Adaptive Panel"
         case .showAdaptivePanelWithCustomGuide: return "Show Adaptive Panel (Custom Layout Guide)"
         case .showCustomStatePanel: return "Show Panel with Custom state"
+        case .showCustomBackdrop: return "Show Panel with Custom Backdrop"
         }
     }
 }
@@ -83,6 +85,7 @@ extension UseCase {
         case .showAdaptivePanel: return .storyboard(String(describing: ImageViewController.self))
         case .showAdaptivePanelWithCustomGuide: return .storyboard(String(describing: AdaptiveLayoutTestViewController.self))
         case .showCustomStatePanel: return .viewController(DebugTableViewController())
+        case .showCustomBackdrop: return .viewController(UIViewController())
         }
     }
 

Examples/Samples/Sources/UseCases/UseCaseController.swift

@@ -273,6 +273,52 @@ extension UseCaseController {
             fpc.set(contentViewController: contentVC)
             fpc.ext_trackScrollView(in: contentVC)
             addMain(panel: fpc)
+
+        case .showCustomBackdrop:
+            class BlurBackdropView: BackdropView {
+                var effectView: UIVisualEffectView!
+                override var alpha: CGFloat {
+                    set {
+                        effectView.alpha = newValue
+                    }
+                    get {
+                        effectView.alpha
+                    }
+                }
+                override init() {
+                    super.init()
+
+                    let effect = UIBlurEffect(style: .prominent)
+                    let effectView = UIVisualEffectView(effect: effect)
+                    addSubview(effectView)
+                    effectView.frame = bounds
+                    effectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
+                    self.effectView = effectView
+                }
+
+                required init?(coder: NSCoder) {
+                    fatalError("init(coder:) has not been implemented")
+                }
+            }
+            class CustomBottomLayout: FloatingPanelBottomLayout {
+                override var anchors: [FloatingPanelState: FloatingPanelLayoutAnchoring]  {
+                    return [
+                        .full: FloatingPanelLayoutAnchor(absoluteInset: 100.0, edge: .top, referenceGuide: .safeArea),
+                        .half: FloatingPanelLayoutAnchor(fractionalInset: 0.5, edge: .bottom, referenceGuide: .safeArea),
+                        .tip: FloatingPanelLayoutAnchor(fractionalInset: 0.1, edge: .bottom, referenceGuide: .safeArea),
+                    ]
+                }
+                override func backdropAlpha(for state: FloatingPanelState) -> CGFloat {
+                    return state == .full ? 0.8 : 0.0
+                }
+            }
+
+            let fpc = FloatingPanelController()
+            fpc.delegate = self
+            fpc.set(contentViewController: contentVC)
+            fpc.backdropView = BlurBackdropView()
+            fpc.layout = CustomBottomLayout()
+            addMain(panel: fpc)
         }
     }
 

Sources/BackdropView.swift

@@ -4,22 +4,22 @@ import UIKit
 
 /// A view that presents a backdrop interface behind a panel.
 @objc(FloatingPanelBackdropView)
-public class BackdropView: UIView {
+open class BackdropView: UIView {
 
     /// The gesture recognizer for tap gestures to dismiss a panel.
     ///
     /// By default, this gesture recognizer is disabled as following the default behavior of iOS modalities.
     /// To dismiss a panel by tap gestures on the backdrop, `dismissalTapGestureRecognizer.isEnabled` is set to true.
     @objc public var dismissalTapGestureRecognizer: UITapGestureRecognizer
 
-    init() {
+    public init() {
         dismissalTapGestureRecognizer = UITapGestureRecognizer()
         dismissalTapGestureRecognizer.isEnabled = false
         super.init(frame: .zero)
         addGestureRecognizer(dismissalTapGestureRecognizer)
     }
 
-    required init?(coder: NSCoder) {
+    required public init?(coder: NSCoder) {
         fatalError("init(coder:) has not been implemented")
     }
 }

Sources/Controller.swift

@@ -158,14 +158,15 @@ open class FloatingPanelController: UIViewController {
 
     /// Returns the surface view managed by the controller object. It's the same as `self.view`.
     @objc
-    public var surfaceView: SurfaceView! {
+    public var surfaceView: SurfaceView {
         return floatingPanel.surfaceView
     }
 
     /// Returns the backdrop view managed by the controller object.
     @objc
-    public var backdropView: BackdropView! {
-        return floatingPanel.backdropView
+    public var backdropView: BackdropView {
+        set { floatingPanel.backdropView = newValue }
+        get { return floatingPanel.backdropView }
     }
 
     /// Returns the scroll view that the controller tracks.

Sources/Core.swift

@@ -10,7 +10,13 @@ class Core: NSObject, UIGestureRecognizerDelegate {
     private weak var ownerVC: FloatingPanelController?
 
     let surfaceView: SurfaceView
-    let backdropView: BackdropView
+    var backdropView: BackdropView {
+        didSet {
+            backdropView.dismissalTapGestureRecognizer
+                .addTarget(self, action: #selector(handleBackdrop(tapGesture:)))
+        }
+    }
+
     let layoutAdapter: LayoutAdapter
     let behaviorAdapter: BehaviorAdapter