Refactor BackdropView.dismissalTapGestureRecognizer

* Added the interface and implementation comment
* Changed the property as non-optional

Author: scenee

Sources/BackdropView.swift

@@ -7,5 +7,19 @@ import UIKit
 public class BackdropView: UIView {
 
     /// The gesture recognizer for tap gestures to dismiss a panel.
-    @objc public var dismissalTapGestureRecognizer: UITapGestureRecognizer!
+    ///
+    /// By default, this gesture recognizer is disabled as following the default behavior of iOS modalities.
+    /// To dismiss a panel by tap gestures on the backrdop, `dismissalTapGestureRecognizer.isEanbled` is set to true.
+    @objc public var dismissalTapGestureRecognizer: UITapGestureRecognizer
+
+    init() {
+        dismissalTapGestureRecognizer = UITapGestureRecognizer()
+        dismissalTapGestureRecognizer.isEnabled = false
+        super.init(frame: .zero)
+        addGestureRecognizer(dismissalTapGestureRecognizer)
+    }
+
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
 }

Sources/Core.swift

@@ -96,11 +96,9 @@ class Core: NSObject, UIGestureRecognizerDelegate {
         panGestureRecognizer.addTarget(self, action: #selector(handle(panGesture:)))
         panGestureRecognizer.delegate = self
 
-        // Set tap-to-dismiss in the backdrop view
-        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleBackdrop(tapGesture:)))
-        tapGesture.isEnabled = false
-        backdropView.dismissalTapGestureRecognizer = tapGesture
-        backdropView.addGestureRecognizer(tapGesture)
+        // Set the tap-to-dismiss action of the backdrop view.
+        // It's disabled by default. See also BackdropView.dismissalTapGestureRecognizer.
+        backdropView.dismissalTapGestureRecognizer.addTarget(self, action: #selector(handleBackdrop(tapGesture:)))
     }
 
     deinit {