TabView: Animations when closing tabs as well

App/Tabs/TabBarView.swift

@@ -11,6 +11,8 @@ class TabView: UIControl
 {
     var active: Bool = false { didSet { setNeedsLayout() } }
     var collapsed: Bool = false
+    var identifier: UUID?
+    
     let label = UILabel(frame: .zero)
     let closeButton = UIButton(frame: .zero)
     let imageView = UIImageView(image: nil)
@@ -104,6 +106,7 @@ protocol TabBarViewDataSource: AnyObject {
     func numberOfTabs(forTabBarView: TabBarView) -> Int
     func tabBarView(_ tabBarView: TabBarView, titleForTabAtIndex: Int) -> String
     func tabBarView(_ tabBarView: TabBarView, imageForTabAtIndex: Int) -> UIImage?
+    func tabBarView(_ tabBarView: TabBarView, uniqueIdentifierForTabAtIndex: Int) -> UUID
 }
 
 protocol TabBarViewDelegate: AnyObject {
@@ -143,29 +146,36 @@ class TabBarView: UIView
     public func reloadTabs(animated: Bool = true) {
         guard let dataSource = self.dataSource else { return }
         
+        var tabViewsRemoved = Set<TabView>(tabViews)
+        
         let numberOfTabs = dataSource.numberOfTabs(forTabBarView: self)
-        while numberOfTabs < tabViews.count {
-            let tabView = tabViews.removeLast()
-            tabView.removeFromSuperview()
-        }
-        
-        while numberOfTabs > tabViews.count {
-            let newTabView = makeTabView()
-            if animated { newTabView.collapsed = true }
-            tabViews.append(newTabView)
-        }
-        
-        for (i, _) in tabViews.enumerated() {
-            self.reloadTab(atIndex: i)
+        for i in 0..<numberOfTabs {
+            let identifier = dataSource.tabBarView(self, uniqueIdentifierForTabAtIndex: i)
+            if let tabView = tabViewsRemoved.first(where: { $0.identifier == identifier }) {
+                tabViewsRemoved.remove(tabView)
+                self.reloadTab(atIndex: i)
+            } else {
+                let newTabView = makeTabView(withIdentifier: identifier)
+                if animated { newTabView.collapsed = true }
+                tabViews.append(newTabView)
+            }
         }
         
         layoutSubviews()
         
         if animated {
+            // Incoming tabs uncollapse
             tabViews.forEach { $0.collapsed = false }
-            UIView.animate(withDuration: 0.3) { [unowned self] in
+            
+            // Outgoing tabs collapse
+            tabViewsRemoved.forEach { $0.collapsed = true }
+            
+            UIView.animate(withDuration: 0.22, delay: 0.0, usingSpringWithDamping: 1.0, initialSpringVelocity: 1.0, options: [], animations: { [unowned self] in
                 layoutSubviews()
-            }
+            }, completion: { [unowned self] finished in
+                tabViewsRemoved.forEach { $0.removeFromSuperview() }
+                tabViews.removeAll { tabViewsRemoved.contains($0) }
+            })
         }
         
         // Adjust scroll offset
@@ -190,8 +200,10 @@ class TabBarView: UIView
         setNeedsLayout()
     }
     
-    private func makeTabView() -> TabView {
+    private func makeTabView(withIdentifier identifier: UUID) -> TabView {
         let tabView = TabView()
+        tabView.identifier = identifier
+        
         tabView.addAction(UIAction(handler: { [unowned self, tabView] _ in
             guard let delegate = self.delegate else { return }
             guard let tabIndex = self.tabViews.firstIndex(of: tabView) else { return }
@@ -244,6 +256,8 @@ class TabBarView: UIView
         for (i, tabView) in tabViews.enumerated() {
             tabContainerView.addSubview(tabView)
             
+            tabView.alpha = tabView.collapsed ? 0.0 : 1.0
+            
             tabView.frame = CGRect(
                 x: xOffset,
                 y: tabContainerBounds.minY,