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

I found the scrollRectToVisible method works better than the setContentOffset.

Swift:

After you catch the click on the tab bar from the delegate, something like below:

func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
 if (viewController.isKindOfClass(SomeControllerClass) && tabBarController.selectedIndex == 0) 
      {
        viewController.scrollToTop()
      }
 }

Now for the scrollToTop function inside the controller:

func scrollToTop()
{
    self.tableView.scrollRectToVisible(CGRectMake(0,0,CGRectGetWidth(self.tableView.frame), CGRectGetHeight(self.tableView.frame)), animated: true)
} 

Answer 2

Implement the UITabBarControllerDelegate method tabBarController:didSelectViewController: to be notified when the user selects a tab. This method is also called when the same tab button is tapped again, even if that tab is already selected.

A good place to implement this delegate would probably be your AppDelegate. Or the object that logically "owns" the tab bar controller.

I would declare and implement a method that can be called on your view controllers to scroll the UICollectionView.

- (void)tabBarController:(UITabBarController *)tabBarController 
 didSelectViewController:(UIViewController *)viewController
{
    static UIViewController *previousController = nil;
    if (previousController == viewController) {
        // the same tab was tapped a second time
        if ([viewController respondsToSelector:@selector(scrollToTop)]) {
            [viewController scrollToTop];
        }
    }
    previousController = viewController;
}

Answer 3

SWIFT 3

Here goes..

First implement the UITabBarControllerDelegate in the class and make sure the delegate is set in viewDidLoad

class DesignStoryStreamVC: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UITabBarControllerDelegate {

 @IBOutlet weak var collectionView: UICollectionView!

 override func viewDidLoad() {
        super.viewDidLoad()

        self.tabBarController?.delegate = self

        collectionView.delegate = self
        collectionView.dataSource = self
    }
}

Next, put this delegate function somewhere in your class.

func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {

    let tabBarIndex = tabBarController.selectedIndex

    print(tabBarIndex)

    if tabBarIndex == 0 {
        self.collectionView.setContentOffset(CGPoint.zero, animated: true)
    }
}

Make sure to select the correct index in the "if" statement. I included the print function so you can double check.

Answer 4

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
    }
}

Answer 5

I have a collection view embedded in a navigation controller, in Swift this works.

var previousController: UIViewController?

func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
    if previousController == viewController {
        if let navVC = viewController as? UINavigationController, vc = navVC.viewControllers.first as? UICollectionViewController {
            vc.collectionView?.setContentOffset(CGPointZero, animated: true)
        }
    }
    previousController = viewController;
}

Answer 6

Swift 5: no need for stored properties in the UITabBarController.

In MyTabBarController.swift, implement tabBarController(_:shouldSelect) to detect when the user re-selects the tab bar item:

protocol TabBarReselectHandling {
    func handleReselect()
}

class MyTabBarController: UITabBarController, UITabBarControllerDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        delegate = self
    }

    func tabBarController(
        _ tabBarController: UITabBarController,
        shouldSelect viewController: UIViewController
    ) -> Bool {
        if tabBarController.selectedViewController === viewController,
            let handler = viewController as? TabBarReselectHandling {
            // NOTE: viewController in line above might be a UINavigationController,
            // in which case you need to access its contents
            handler.handleReselect()
        }

        return true
    }
}

In MyTableViewController.swift, handle the re-selection by scrolling the table view to the top:

class MyTableViewController: UITableViewController, TabBarReselectHandling {
    func handleReselect() {
        tableView?.setContentOffset(.zero, animated: true)
    }
}

Now you can easily extend this to other tabs by just implementing TabBarReselectHandling.