Allow opting out of appearance transition callbacks on presenting view controller

PanModal/Animator/PanModalPresentationAnimator.swift

@@ -71,8 +71,11 @@ public class PanModalPresentationAnimator: NSObject {
 
         let presentable = panModalLayoutType(from: transitionContext)
 
-        // Calls viewWillAppear and viewWillDisappear
-        fromVC.beginAppearanceTransition(false, animated: true)
+        let isAppearanceTransition = presentable?.isAppearanceTransition ?? true
+        if isAppearanceTransition {
+            // Calls viewWillAppear and viewWillDisappear
+            fromVC.beginAppearanceTransition(false, animated: true)
+        }
 
         // Presents the view in shortForm position, initially
         let yPos: CGFloat = presentable?.shortFormYPos ?? 0.0
@@ -92,8 +95,10 @@ public class PanModalPresentationAnimator: NSObject {
         PanModalAnimator.animate({
             panView.frame.origin.y = yPos
         }, config: presentable) { [weak self] didComplete in
-            // Calls viewDidAppear and viewDidDisappear
-            fromVC.endAppearanceTransition()
+            if isAppearanceTransition {
+                // Calls viewDidAppear and viewDidDisappear
+                fromVC.endAppearanceTransition()
+            }
             transitionContext.completeTransition(didComplete)
             self?.feedbackGenerator = nil
         }
@@ -109,18 +114,24 @@ public class PanModalPresentationAnimator: NSObject {
             let fromVC = transitionContext.viewController(forKey: .from)
             else { return }
 
-        // Calls viewWillAppear and viewWillDisappear
-        toVC.beginAppearanceTransition(true, animated: true)
-
         let presentable = panModalLayoutType(from: transitionContext)
+
+        let isAppearanceTransition = presentable?.isAppearanceTransition ?? true
+        if isAppearanceTransition {
+            // Calls viewWillAppear and viewWillDisappear
+            toVC.beginAppearanceTransition(true, animated: true)
+        }
+
         let panView: UIView = transitionContext.containerView.panContainerView ?? fromVC.view
 
         PanModalAnimator.animate({
             panView.frame.origin.y = transitionContext.containerView.frame.height
         }, config: presentable) { didComplete in
             fromVC.view.removeFromSuperview()
-            // Calls viewDidAppear and viewDidDisappear
-            toVC.endAppearanceTransition()
+            if isAppearanceTransition {
+                // Calls viewDidAppear and viewDidDisappear
+                toVC.endAppearanceTransition()
+            }
             transitionContext.completeTransition(didComplete)
         }
     }

PanModal/Presentable/PanModalPresentable+Defaults.swift

@@ -97,6 +97,10 @@ public extension PanModalPresentable where Self: UIViewController {
         return shouldRoundTopCorners
     }
 
+    var isAppearanceTransition: Bool {
+        return true
+    }
+
     func shouldRespond(to panModalGestureRecognizer: UIPanGestureRecognizer) -> Bool {
         return true
     }

PanModal/Presentable/PanModalPresentable.swift

@@ -173,6 +173,15 @@ public protocol PanModalPresentable: AnyObject {
      */
     var showDragIndicator: Bool { get }
 
+    /**
+     A flag to determine whether view lifecycle methods `view(Will|Did)(A|Disa)ppear` are called on the presenting view controller.
+
+     Since pan modal presentation does not remove the presenting view from the view hierarchy, it may not be desirable to call the relevant methods that are usually associated with removing the presenting view from the view hierarchy.
+
+     Default value is true.
+     */
+    var isAppearanceTransition: Bool { get }
+
     /**
      Asks the delegate if the pan modal should respond to the pan modal gesture recognizer.
 

Tests/PanModalTests.swift

@@ -60,6 +60,7 @@ class PanModalTests: XCTestCase {
         XCTAssertEqual(vc.shouldRoundTopCorners, false)
         XCTAssertEqual(vc.showDragIndicator, false)
         XCTAssertEqual(vc.shouldRoundTopCorners, false)
+        XCTAssertEqual(vc.isAppearanceTransition, true)
         XCTAssertEqual(vc.cornerRadius, 8.0)
         XCTAssertEqual(vc.transitionDuration, PanModalAnimator.Constants.defaultTransitionDuration)
         XCTAssertEqual(vc.transitionAnimationOptions, [.curveEaseInOut, .allowUserInteraction, .beginFromCurrentState])