两个独立的UIViewControllers上的UITabBarControllerDelegate-Swift

Question

I have the following code that i'm trying to achieve a "scroll to top" on a UIViewcontroller and "scroll to beginning" on another UIViewController.

The first VC has a table view and the second VC has a collection view.

-NearMeViewController-
override func viewDidLoad() {
        super.viewDidLoad()
        self.tabBarController?.delegate = self
        //....
}
extension NearMeViewController: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        let tabBarIndex = tabBarController.selectedIndex
        if tabBarIndex == 0 {
            self.nearMeTable.setContentOffset(CGPoint.zero, animated: true)
        }
    }
}

-MapSearchViewController-
override func viewDidLoad() {
        super.viewDidLoad()
        self.tabBarController?.delegate = self
        //....
}

extension MapSearchViewController: UITabBarControllerDelegate {
    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        let tabBarIndex = tabBarController.selectedIndex
        if tabBarIndex == 2 && requests.mapEventData.count > 0 {
            self.resultsCollectionView?.scrollToItem(at: IndexPath(row: 0, section: 0),
                                                     at: .left,
                                                     animated: true)
        }
    }
}

They are both connected to the same UITabBar of course. The issue is that when i open the app, and i press the tabBarIndex 0 it scrolls to top of the table view.

Then i change VC and i try to press the tabBarIndex 2, so it takes me to the first item of the collection view.

Afterwards I go back to the first VC and when i try to press the tabBarIndex 0, the tableview is not scrolling to top (as it was doing when i first opened the app).

But the second VC with the collection view is working fine.

Any idea why this might happen?

Answer 1

It looks like you are checking the tabBarController's .selectedIndex ... but that is the index of the currently showing tab, not the tab you are "on your way to."

More likely, you want to use code similar to this:

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

    if let vc = viewController as? MapSearchViewController {
        // user tapped Map Search tab item
    }

    if let vc = viewController as? NearMeViewController {
        // user tapped Near Me tab item
    }

}

Edit: Here is a simple example, using a subClassed UITabBarController.

Set up your storyboard as normal, creating View Controllers and connecting them as "Tabs", then set the Custom Class of the TabBarController to MyTabBarController . This sample code will (hopefully) be easy to follow.

A runnable example is at: https://github.com/DonMag/SWTabBarSubclass

//
//  TabBarSample.swift
//

import UIKit

class FirstViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // all your normal setup stuff....
    }

    func firstViewSpecific(_ aValue: Int) -> Void {
        print("Passed value is:", aValue)
        // do something with the passed value
    }

}

class NearMeViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // all your normal setup stuff....
    }

    func resetMe() -> Void {
        print("resetMe() called in NearMeVC")
        // do whatever you want, such as
        self.nearMeTable.setContentOffset(CGPoint.zero, animated: true)
    }

}

class MapSearchViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // all your normal setup stuff....
    }

    func resetMe() -> Void {
        print("resetMe() called in MapSearchVC")
        // do whatever you want, such as
        if requests.mapEventData.count > 0 {
            self.resultsCollectionView?.scrollToItem(at: IndexPath(row: 0, section: 0),
                                                     at: .left,
                                                     animated: true)
        }
    }

}

class MyTabBarController: UITabBarController, UITabBarControllerDelegate {

    var myValue = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        // make self the UITabBarControllerDelegate
        self.delegate = self
    }

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

        if let vc = viewController as? FirstViewController {
            myValue += 1
            vc.firstViewSpecific(myValue)
            return
        }

        if let vc = viewController as? NearMeViewController {
            vc.resetMe()
            return
        }

        if let vc = viewController as? MapSearchViewController {
            vc.resetMe()
            return
        }

    }

}

Answer 2

viewDidLoad is not being called each time the VC appears but only once (or when it was deallocated before)

the delegate of vc 0 is set only once... and then vc1 is loaded and set as delegate... but then not vc0 again.

to make it work, set the delegate in viewWillAppear.

note

changing the delegate over and over for this is weird... and checking the index is fragile at best go with DonMag's solution.

Answer 3

might not apply to all scenarios, check if your VC has been set to

self.tabBarController?.delegate = self

within your ViewDidLoad()