Issue #990
In many popular apps like LinkedIn, Reddit, we can tap again on a bar bar item to scroll to top. Although this behavior is not built in by iOS, we can implement that very easily.
The idea is to keep track of previous selection so we can compare if user has indeed tapped on the tab bar item again.
final class TabBarController: UITabBarController {
override var selectedViewController: UIViewController? {
didSet {
if previousSelectedViewController == selectedViewController {
onTapAgain?()
}
previousSelectedViewController = selectedViewController
}
}
var onTapAgain: (() -> Void)?
private weak var previousSelectedViewController: UIViewController?
}
Here we use selectedviewcontroller, which is changed when user manually changes the selected index path. It is same as we observe UITabBarControllerDelegate ’s tabBarController(_:didSelect:)
The selectedindex, however, is called when we change selectedIndex property, not when user changes selectedviewcontroller
Then we can handle to call scrollToItem
private func handleOnTapAgain() {
guard
let navigationController = tabBarController?.selectedViewController as? UINavigationController,
let viewController = navigationController.topViewController as? UICollectionViewController,
viewController.collectionView.numberOfSections > 0,
viewController.collectionView.numberOfItems(inSection: 0) > 0
else { return }
viewController.collectionView.scrollToItem(at: IndexPath(item: 0, section: 0), at: .top, animated: true)
}
Or we can simply set content offset
viewController.collectionView.setContentOffset(.zero, animated: true)
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