Use spring animation for presenting sheet

Sources/SheetController/SheetContainerDismissAnimationController.swift

@@ -11,7 +11,7 @@ import UIKit
 class SheetContainerDismissAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
 
     func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
-        return 0.35
+        return 0.5
     }
     
     func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
@@ -36,7 +36,8 @@ class SheetContainerDismissAnimationController: NSObject, UIViewControllerAnimat
         
         if let initialVelocity = fromVC.dismissAnimationInitialVelocity {
             let vector = CGVector(dx: initialVelocity, dy: 0)
-            let parameters = UISpringTimingParameters(dampingRatio: 1, initialVelocity: vector)
+            let damping = SheetContainerViewController.springDamping
+            let parameters = UISpringTimingParameters(dampingRatio: damping, initialVelocity: vector)
             animator = UIViewPropertyAnimator(duration: duration, timingParameters: parameters)
         } else {
             animator = UIViewPropertyAnimator(duration: duration, curve: .easeOut)

Sources/SheetController/SheetContainerPresentationAnimationController.swift

@@ -11,7 +11,7 @@ import UIKit
 class SheetContainerPresentationAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
 
     func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
-        return 0.35
+        return 0.5
     }
     
     func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
@@ -31,22 +31,28 @@ class SheetContainerPresentationAnimationController: NSObject, UIViewControllerA
         container.addSubview(dimmingView)
         container.addSubview(toVC.view)
         
-        toVC.view.transform = CGAffineTransform(translationX: 0, y: toVC.initialConstant)
+        let initialConstant = toVC.initialConstant
+        toVC.topConstraint.constant = toVC.view.bounds.height
+        toVC.view.layoutIfNeeded()
         
         let duration = transitionDuration(using: transitionContext)
-        UIView.animate(withDuration: duration, animations: {
+        let damping = SheetContainerViewController.springDamping
+        let pointsPerSecond: CGFloat = 50
+        let velocity = pointsPerSecond / initialConstant
+        UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: damping, initialSpringVelocity: velocity, options: []) {
             // we animate the dimming view's frame so that it doesn't go under the content view, in case there's a transparent background
             // we also extend the dimming view under any rounded corners the content view has
-            dimmingView.frame = CGRect(x: 0, y: 0, width: dimmingView.bounds.width, height: toVC.initialConstant + toVC.content.view.layer.cornerRadius)
+            dimmingView.frame = CGRect(x: 0, y: 0, width: dimmingView.bounds.width, height: initialConstant + toVC.content.view.layer.cornerRadius)
             dimmingView.alpha = toVC.dimmingView.alpha
-            toVC.view.transform = .identity
-        }, completion: { (finished) in
+            toVC.topConstraint.constant = initialConstant
+            toVC.view.layoutIfNeeded()
+        } completion: { (finished) in
             dimmingView.removeFromSuperview()
             toVC.dimmingView.isHidden = false
             
             toVC.view.frame = finalFrame
             transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
-        })
+        }
 
     }
     

Sources/SheetController/SheetContainerViewController.swift

@@ -31,6 +31,8 @@ public extension SheetContainerViewControllerDelegate {
 
 open class SheetContainerViewController: UIViewController {
 
+    internal static let springDamping: CGFloat = 0.75
+    
     public weak var delegate: SheetContainerViewControllerDelegate?
     
     public let content: UIViewController
@@ -224,7 +226,8 @@ open class SheetContainerViewController: UIViewController {
         if delegate?.sheetContainer(self, willSnapToDetent: springToDetent.0) ?? true {
             self.topConstraint.constant = springToDetent.1
             
-            UIView.animate(withDuration: 0.35, delay: 0, usingSpringWithDamping: 0.75, initialSpringVelocity: springVelocity, animations: {
+            let damping = SheetContainerViewController.springDamping
+            UIView.animate(withDuration: 0.35, delay: 0, usingSpringWithDamping: damping, initialSpringVelocity: springVelocity, animations: {
                 self.view.layoutIfNeeded()
                 self.dimmingView.alpha = lerp(springToDetent.1, min: self.topDetent.offset, max: self.bottomDetent.offset, from: self.maximumDimmingAlpha, to: self.minimumDimmingAlpha)
             }, completion: { (finished) in