Add sheet container delegate

SheetImagePicker/Detent.swift

@@ -8,7 +8,7 @@
 
 import UIKit
 
-public enum Detent {
+public enum Detent: Equatable {
     case top
     case middle
     case bottom

SheetImagePicker/SheetContainerViewController.swift

@@ -8,16 +8,29 @@
 
 import UIKit
 
+public protocol SheetContainerViewControllerDelegate {
+    func sheetContainer(_ sheetContainer: SheetContainerViewController, willSnapToDetent detent: Detent) -> Bool
+    func sheetContainer(_ sheetContainer: SheetContainerViewController, didSnapToDetent detent: Detent)
+}
+
+// default no-op implementation
+public extension SheetContainerViewControllerDelegate {
+    func sheetContainer(_ sheetContainer: SheetContainerViewController, willSnapToDetent detent: Detent) -> Bool {
+        return true
+    }
+    func sheetContainer(_ sheetContainer: SheetContainerViewController, didSnapToDetent detent: Detent) {}
+}
+
 public class SheetContainerViewController: UIViewController {
 
+    public var delegate: SheetContainerViewControllerDelegate?
+    
     let content: UIViewController
     
-    public var detents: [Detent] = [.bottom, .middle, .top] {
+    public var detents: [Detent] = [.bottom, .middle, .top]
-        didSet {
+    var topDetent: (detent: Detent, offset: CGFloat) {
-            sortDetents()
+        return detents.map { ($0, $0.offset(in: view)) }.min(by: { $0.1 < $1.1 })!
     }
-    }
-    var sortedDetentOffsets: [CGFloat] = []
 
     var topConstraint: NSLayoutConstraint!
     lazy var initialConstant: CGFloat = view.bounds.height / 2
@@ -53,18 +66,6 @@ public class SheetContainerViewController: UIViewController {
         content.view.addGestureRecognizer(panGesture)
     }
 
-    public override func viewDidLayoutSubviews() {
-        super.viewDidLayoutSubviews()
-        
-        sortDetents()
-    }
-    
-    private func sortDetents() {
-        sortedDetentOffsets = detents.map {
-            $0.offset(in: view)
-        }.sorted()
-    }
-    
     @objc func panGestureRecognized(_ recognizer: UIPanGestureRecognizer) {
         switch recognizer.state {
         case .began:
@@ -73,7 +74,7 @@ public class SheetContainerViewController: UIViewController {
         case .changed:
             let translation = recognizer.translation(in: content.view)
             var realOffset = initialConstant + translation.y
-            if realOffset < sortedDetentOffsets.first! {
+            if realOffset < topDetent.offset {
                 func clamp(_ value: CGFloat, from: CGFloat, to: CGFloat) -> CGFloat {
                     if value < from {
                         return from
@@ -88,7 +89,7 @@ public class SheetContainerViewController: UIViewController {
                     // 3x^2 - 2x^3
                     return 3 * pow(x, 2) - 2 * pow(x, 3)
                 }
-                let topOffset = sortedDetentOffsets.first!
+                let topOffset = topDetent.offset
                 let smoothed = smoothstep(value: realOffset, from: topOffset, to: 0)
                 realOffset = topOffset - smoothed * maximumStretchDistance
                 
@@ -98,37 +99,46 @@ public class SheetContainerViewController: UIViewController {
         case .ended:
             let velocity = recognizer.velocity(in: view)
 
-            let springToDetent: CGFloat
+            let springToDetent: (Detent, CGFloat)
             if abs(velocity.y) > minimumDetentJumpVelocity,
-                let offsetInVelocityDirection = nearestDetentOffset(currentOffset: topConstraint.constant, direction: velocity.y) {
+                let detentInVelocityDirection = nearestDetentOffset(currentOffset: topConstraint.constant, direction: velocity.y) {
-                springToDetent = offsetInVelocityDirection
+                springToDetent = detentInVelocityDirection
-            } else if let nearestOffset = nearestDetentOffset(currentOffset: topConstraint.constant) {
+            } else if let nearestDetent = nearestDetentOffset(currentOffset: topConstraint.constant) {
-                springToDetent = nearestOffset
+                springToDetent = nearestDetent
             } else {
                 return
             }
             
-            let springDistance = abs(topConstraint.constant - springToDetent)
+            if delegate?.sheetContainer(self, willSnapToDetent: springToDetent.0) ?? true {
-            self.topConstraint.constant = springToDetent
+                let springDistance = abs(topConstraint.constant - springToDetent.1)
+                self.topConstraint.constant = springToDetent.1
                 let springVelocity = velocity.y / springDistance
                 
                 UIView.animate(withDuration: 0.35, delay: 0, usingSpringWithDamping: 0.6, initialSpringVelocity: springVelocity, animations: {
                     self.view.layoutIfNeeded()
+                }, completion: { (finished) in
+                    self.delegate?.sheetContainer(self, didSnapToDetent: springToDetent.0)
                 })
+            }
         default:
             return
         }
     }
     
-    func nearestDetentOffset(currentOffset: CGFloat) -> CGFloat? {
+    func nearestDetentOffset(currentOffset: CGFloat) -> (Detent, CGFloat)? {
-        return sortedDetentOffsets.min(by: { abs($0 - currentOffset) < abs($1 - currentOffset) })
+        return detents.map { ($0, $0.offset(in: view)) }.min { (a, b) -> Bool in
+            return abs(a.1 - currentOffset) < abs(b.1 - currentOffset)
+        }
     }
     
-    func nearestDetentOffset(currentOffset: CGFloat, direction: CGFloat) -> CGFloat? {
+    func nearestDetentOffset(currentOffset: CGFloat, direction: CGFloat) -> (Detent, CGFloat)? {
+        let sorted = detents.map { ($0, $0.offset(in: view)) }.sorted { (a, b) -> Bool in
+            return a.1 < b.1
+        }
         if direction < 0 {
-            return sortedDetentOffsets.last(where: { $0 < currentOffset })
+            return sorted.last(where: { $0.1 < currentOffset })
         } else {
-            return sortedDetentOffsets.first(where: { $0 > currentOffset })
+            return sorted.first(where: { $0.1 > currentOffset })
         }
     }
     

SheetImagePickerTest/ViewController.swift

@@ -19,6 +19,8 @@ class ViewController: UIViewController {
         content.view.translatesAutoresizingMaskIntoConstraints = false
         content.view.backgroundColor = .red
         let sheet = SheetContainerViewController(content: content)
+        sheet.delegate = self
+        sheet.detents = [.bottom, .middle, .top]
         sheet.view.backgroundColor = .blue
         
         addChild(sheet)
@@ -34,3 +36,18 @@ class ViewController: UIViewController {
 
 }
 
+extension ViewController: SheetContainerViewControllerDelegate {
+    func sheetContainer(_ sheetContainer: SheetContainerViewController, willSnapToDetent detent: Detent) -> Bool {
+        if detent == .bottom {
+            UIView.animate(withDuration: 0.35, animations: {
+                sheetContainer.view.transform = CGAffineTransform(translationX: 0, y: sheetContainer.view.bounds.height)
+            }, completion: { (finished) in
+                sheetContainer.removeFromParent()
+                sheetContainer.didMove(toParent: nil)
+                sheetContainer.view.removeFromSuperview()
+            })
+            return false
+        }
+        return true
+    }
+}