Fix delegations never fired on tab swipe

Sources/iOS/TabBar.swift

@@ -183,13 +183,13 @@ public protocol TabBarDelegate {
 @objc(_TabBarDelegate)
 internal protocol _TabBarDelegate {
   /**
-   A delegation method that is executed when the tabItem will trigger the
-   animation to the next tab.
+   A delegation method that is executed to determine if the TabBar should
+   transition to the next tab.
    - Parameter tabBar: A TabBar.
    - Parameter tabItem: A TabItem.
+   - Returns: A Boolean.
    */
-  @objc
-  optional func _tabBar(tabBar: TabBar, willSelect tabItem: TabItem)
+  func _tabBar(tabBar: TabBar, shouldSelect tabItem: TabItem) -> Bool
 }
 
 @objc(TabBarStyle)
@@ -546,6 +546,9 @@ fileprivate extension TabBar {
       return
     }
 
+    guard !(false == _delegate?._tabBar(tabBar: self, shouldSelect: tabItem)) else { return }
+
+
     animate(to: tabItem, isTriggeredByUserInteraction: true)
   }
 }
@@ -592,7 +595,6 @@ fileprivate extension TabBar {
    */
   func animate(to tabItem: TabItem, isTriggeredByUserInteraction: Bool, completion: ((TabItem) -> Void)? = nil) {
     if isTriggeredByUserInteraction {
-      _delegate?._tabBar?(tabBar: self, willSelect: tabItem)
       delegate?.tabBar?(tabBar: self, willSelect: tabItem)
     }
 

Sources/iOS/TabsController.swift

@@ -257,7 +257,6 @@ fileprivate extension TabsController {
   func prepareTabBar() {
     tabBar.lineAlignment = .bottom == tabBarAlignment ? .top : .bottom
     tabBar._delegate = self
-    tabBar.delegate = self
     view.addSubview(tabBar)
   }
 
@@ -374,10 +373,10 @@ fileprivate extension TabsController {
       switch swipeGesture.direction {
       case .right:
         guard (selectedIndex - 1) >= 0 else { return }
-        select(at: selectedIndex - 1)
+        internalSelect(at: selectedIndex - 1, isTriggeredByUserInteraction: true)
       case .left:
         guard (selectedIndex + 1) < viewControllers.count else { return }
-        select(at: selectedIndex + 1)
+        internalSelect(at: selectedIndex + 1, isTriggeredByUserInteraction: true)
       default:
         break
       }
@@ -391,8 +390,26 @@ extension TabsController {
    - Parameter at index: An Int.
    */
   open func select(at index: Int) {
+    internalSelect(at: index, isTriggeredByUserInteraction: false)
+  }
+
+  /**
+   Transitions to the view controller that is at the given index.
+   - Parameter at index: An Int.
+   - Parameter isTriggeredByUserInteraction: A boolean indicating whether the
+   state was changed by a user interaction, true if yes, false otherwise.
+   - Returns: A boolean indicating whether the transition will take place.
+   */
+  @discardableResult
+  private func internalSelect(at index: Int, isTriggeredByUserInteraction: Bool) -> Bool {
     guard index != selectedIndex else {
-      return
+      return false
+    }
+
+    if isTriggeredByUserInteraction {
+      guard !(false == delegate?.tabsController?(tabsController: self, shouldSelect: viewControllers[index])) else {
+        return false
+      }
     }
 
     Motion.async { [weak self] in
@@ -402,42 +419,26 @@ extension TabsController {
 
       s.tabBar.select(at: index)
 
-      s.transition(to: s.viewControllers[index], isTriggeredByUserInteraction: false) { [weak self] (isFinishing) in
+      s.transition(to: s.viewControllers[index], isTriggeredByUserInteraction: isTriggeredByUserInteraction) { [weak self] (isFinishing) in
         guard isFinishing else {
           return
         }
 
         self?.selectedIndex = index
       }
     }
+    return true
   }
 }
 
-extension TabsController: TabBarDelegate, _TabBarDelegate {
+extension TabsController: _TabBarDelegate {
   @objc
-  func _tabBar(tabBar: TabBar, willSelect tabItem: TabItem) {
-    guard !(false == tabBar.delegate?.tabBar?(tabBar: tabBar, shouldSelect: tabItem)) else {
-      return
-    }
+  func _tabBar(tabBar: TabBar, shouldSelect tabItem: TabItem) -> Bool {
 
     guard let i = tabBar.tabItems.index(of: tabItem) else {
-      return
-    }
-
-    guard i != selectedIndex else {
-      return
-    }
-
-    guard !(false == delegate?.tabsController?(tabsController: self, shouldSelect: viewControllers[i])) else {
-      return
+      return false
     }
 
-    transition(to: viewControllers[i], isTriggeredByUserInteraction: true) { [weak self] (isFinishing) in
-      guard isFinishing else {
-        return
-      }
-
-      self?.selectedIndex = i
-    }
+    return internalSelect(at: i, isTriggeredByUserInteraction: true)
   }
 }