Update current UIViewController UI upon tap of TabBar

Question

I am trying to show an activity indicator when a user taps a certain TabBar item. My problem, I think, lies in the fact that the UI Main thread is frozen.

When a user taps the TabBar I prepare a big data list that takes about six seconds. I get the activity to show everywhere but when they tap the TabBar.

It seems as though the indicator is "running" because when the segued uitableviewcontroller shows, it is showing the indicator. But this is too late and dispatch doesn't seem to do anything either.

func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
    if let visibleViewCtrl = UIApplication.shared.keyWindow?.visibleViewController {
        // do whatever you want with your `visibleViewCtrl`
        print (String.init(describing: visibleViewCtrl.classForCoder))
        DispatchQueue.main.async{

            let aprogressView = ProgressView(Message: "Filtering...",
                                        Theme:.Dark,
                                        IsModal:true);

            visibleViewCtrl.view.addSubview(aprogressView)
            aprogressView.show()
        }
    }
    return true
}

OK, So the problem is that it is going to a tableview controller, which tries to get rows in section almost immediatetly, which then first the fetchrequest which blocks everything as it is on the main thread.

put the indictor code in dispatchqueue.main.async { } block in target view controller — teodik abrami, Feb 04 '19 at 22:30
Add this code in view did load method of your view controller and after showing activity indicator prepare the data list. — Mahak Mittal, Feb 05 '19 at 05:08
We need to see code to understand how the data is being prepared. If you're doing that on the main queue from the viewController about to be presented, then it'll freeze the UI until it's finished and then present (showing your progress view) — Andrew Tetlaw, Feb 05 '19 at 08:34
dont put the dispatchqueue code in method put it in viewcontroller viewdidload which tab bar opening it — teodik abrami, Feb 05 '19 at 09:40
@AndrewTetlaw That is exactly what is happening. I edited my question to reflect that. — jimijon, Feb 05 '19 at 13:15

score 0 · Answer 1 · edited Feb 05 '19 at 19:13

SOLVED:

Added a boolean:

 var loadData = false

 override func viewDidAppear(_ animated: Bool) {
        loadData = true
        self.tableView.reloadData()
 }

Then the delegates:

func sectionIndexTitles(for tableView: UITableView) -> [String]? {
    if loadData == false {
        return nil
    }
    return  searchFetchedResultsController.sectionIndexTitles

}



func numberOfSections(in tableView: UITableView) -> Int {
    if loadData == false {
        return 0
    }

Now it will transition to the new controller immediately and thus I can now show feedback from viewWillAppear :

appDelegate.progressView = ProgressView(Message: "Filtering Brands", Theme:.Dark, IsModal:true);
    appDelegate.progressView!.show()

This will NOT work with programatical display

    self.navigationController?.pushViewController(vc, animated: false)

You can now accept your own solution. Do not put solutions in the question. Thank you. — Brian Tompsett - 汤莱恩, Feb 05 '19 at 19:14

Update current UIViewController UI upon tap of TabBar

1 Answers1