Tap tab bar to scroll to top of UITableViewController

Question

Tapping the tab bar icon for the current navigation controller already returns the user to the root view, but if they are scrolled way down, if they tap it again I want it t

Answer 1

In this implementation you no need static variable and previous view controller state

If your UITableViewController in UINavigationController you can implement protocol and function:

protocol ScrollableToTop {
    func scrollToTop()
}

extension UIScrollView {
    func scrollToTop(_ animated: Bool) {
        var topContentOffset: CGPoint
        if #available(iOS 11.0, *) {
            topContentOffset = CGPoint(x: -safeAreaInsets.left, y: -safeAreaInsets.top)
        } else {
            topContentOffset = CGPoint(x: -contentInset.left, y: -contentInset.top)
        }
        setContentOffset(topContentOffset, animated: animated)
    }
}

Then in your UITableViewController:

class MyTableViewController: UITableViewController: ScrollableToTop {
   func scrollToTop() {
    if isViewLoaded {
        tableView.scrollToTop(true)
    }
   }
}

Then in UITabBarControllerDelegate:

extension MyTabBarController: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
        guard tabBarController.selectedViewController === viewController else { return true }
        guard let navigationController = viewController as? UINavigationController else {
            assertionFailure()
            return true
        }
        guard
            navigationController.viewControllers.count <= 1,
            let destinationViewController = navigationController.viewControllers.first as? ScrollableToTop
        else {
            return true
        }
        destinationViewController.scrollToTop()
        return false
    }
}