Scroll to the current session instead of just scrolling to the top

Author: zats

trySwift/RootTabBar/RootTabBarController.swift

@@ -15,23 +15,33 @@ class RootTabBarController: UITabBarController, UITabBarControllerDelegate {
   }
 
   func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
-    if let splitViewController = viewController as? UISplitViewController {
-      if let navigationController = splitViewController.viewControllers.last as? UINavigationController {
-        if navigationController.viewControllers.count > 1 {
-          navigationController.popViewController(animated: true)
+    guard
+      let splitViewController = viewController as? UISplitViewController,
+      let navigationController = splitViewController.viewControllers.last as? UINavigationController
+      else {
+        return
+    }
+
+    // if several view controllers are in the stack, pop to the root
+    if navigationController.viewControllers.count > 1 {
+      navigationController.popToRootViewController(animated: true)
+    } else {
+      // if there's at least one view controller in the stack (which there always should be)
+      if let firstController = navigationController.viewControllers.first {
+        // we either delegate to the controller since it knows better how to scroll to the top
+        if let scrollableToTop = firstController as? ScrollableToTop {
+          scrollableToTop.scrollAfterTabTap()
+        // or we find the topmost scroll view and scroll it to the top
         } else {
-          navigationController.viewControllers.first?.scrollToTop()
+          firstController.view.findScrollSubview()?.setContentOffset(.zero, animated: true)
         }
       }
     }
   }
 }
 
-private extension UIViewController {
-  func scrollToTop() {
-    let scrollView = view.findScrollSubview()
-    scrollView?.setContentOffset(.zero, animated: true)
-  }
+protocol ScrollableToTop {
+  func scrollAfterTabTap()
 }
 
 private extension UIView {

trySwift/ScheduleViewController.swift

@@ -35,7 +35,6 @@ class ScheduleViewController: ButtonBarPagerTabStripViewController {
 
     override func viewControllers(for pagerTabStripController: PagerTabStripViewController) -> [UIViewController] {
         return days.map { SessionsTableViewController(conferenceDay: $0, scheduleViewController: self) }
-
     }
 
     override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
@@ -47,6 +46,13 @@ class ScheduleViewController: ButtonBarPagerTabStripViewController {
     }
 }
 
+extension ScheduleViewController: ScrollableToTop {
+  func scrollAfterTabTap() {
+    let controller = viewControllers[currentIndex] as! SessionsTableViewController
+    controller.scrollAfterTabTap()
+  }
+}
+
 private extension ScheduleViewController {
 
     func moveToCorrectDate() {

trySwift/SessionsTableViewController.swift

@@ -10,6 +10,7 @@ import UIKit
 import XLPagerTabStrip
 import TrySwiftData
 
+
 class SessionsTableViewController: UITableViewController {
 
     var conferenceDay: ConferenceDay
@@ -216,3 +217,36 @@ private extension SessionsTableViewController {
         return workshopDetailVC
     }
 }
+
+extension SessionsTableViewController: ScrollableToTop {
+  func scrollAfterTabTap() {
+    if tableView.contentOffset.y > 1 {
+      tableView.setContentOffset(.zero, animated: true)
+    } else {
+      scrollToCurrentTime()
+    }
+  }
+
+  private func scrollToCurrentTime() {
+    // find current block
+    tableView.scrollToRow(at: IndexPath(row: 0, section: currentBlockIndex()),
+                          at: UITableViewScrollPosition.middle,
+                          animated: true)
+  }
+
+  private func currentBlockIndex() -> Int {
+    let time = Date()
+    // if current time is within any given session, return its index,
+    // if the time is earlier than the first session, return first session
+    // otherwise return last session
+    if let offset = conferenceDay.sessionBlocks.enumerated().first(where: {
+      $0.element.startTime <= time && $0.element.endTime >= time
+    })?.offset {
+      return offset
+    } else if let block = conferenceDay.sessionBlocks.first, block.startTime > time {
+      return 0
+    } else {
+      return conferenceDay.sessionBlocks.count - 1
+    }
+  }
+}