Sharing data between tabs using XLPagerTabStrip

Question

I'm using XLPagerTabStrip - https://github.com/xmartlabs/XLPagerTabStrip to have two tabs which share the same dataset.

For the data set, in my main view (which hosts two tabs) I have a call to Firebase to get the data. Once received I make a Notification call to post the data -> N.B. I'm sure this isn't the most elegant way of doing this so if anyone has suggestions on a better way please let me know (albeit thats a separate question in itself).

Anyway - in both tabs I have observers for this notification.

This works great on the initial tab, however it appears the 2nd tab is not initialised until the User taps on the tab -> makes sense for memory reasons :) But this means the post in MainVC gets missed...

How can I get both tabs to essentially use the same dataset from a Firebase call?

My high level code is as follows (I can add more detail if required, let me know whats missing ):

class MainVC: ButtonBarPagerTabStripViewController {
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        getData()
    }

    fileprivate func getData() {
        // ... bunch of firebase stuff...

        NotificationCenter.default.post(
            name: NSNotification.Name(rawValue: "dataReceived"),
            object: nil,
            userInfo: ["data": data]
        )
    }

    override func viewControllers(for pagerTabStripController: PagerTabStripViewController) -> [UIViewController] {
        let tab_one = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "tab_one")

        let tab_two = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "tab_two")

        return [tab_one, tab_two]
    }
}

class TabOneVC: UIViewController, IndicatorInfoProvider {

    override func viewDidLoad() {
        super.viewDidLoad()

        print("Hello from Tab One")

        NotificationCenter.default.addObserver(
          self,
          selector: #selector(dataReceivedHandler(notfication:)),
          name: NSNotification.Name(rawValue: "dataReceived"),
          object: nil
        )
    }

    @objc func dataReceivedHandler(notfication: NSNotification) {
        // ... process data received
    }
}

class TabTwoVC: UIViewController, IndicatorInfoProvider {

    override func viewDidLoad() {
        super.viewDidLoad()

        print("Hello from Tab Two")

        ... same notification code as per Tab One 
    }
}

I suppose Core Data might be needed instead but I will only go down that route if its the only way (without horrendous hacks)

Thanks in advance!

Answer 1

So I managed to get this working but not entirely sure if this is the best way so will leave this open for a little bit

What I done is to have MainVC reload the view

The Tab VCs both shares the same data property in MainVC - which is what I think you were suggesting Ajay...

class MainVC: ButtonBarPagerTabStripViewController {

    var data: [DataModel] = []

    fileprivate func getData() {
        // ... bunch of firebase stuff...

        // assign the data
        self.data = data

        // reload the view now we have data 
        // (doubt this is good practice...)
        self.reloadPagerTabStripView()
    }
}

Both tabs get the data from MainVC like so...

class TabOneVC: UIViewController, IndicatorInfoProvider {
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        // Get data in MainVC
        if let mainVC = self.parent as? MainVC {
            data = mainVC.data // woohoo :)
        }
    }
}

Answer 2

As you know that XLpagertabstrip work like UITabbarController, mean your ButtonBarPagerTabStripViewController treat your both TabOneVC and TabTwoVC as childViewControllers. so in my opinion you should access both viewControllers and send data without Notification.

So access your both viewControllers from getData() method of your ButtonBarPagerTabStripViewController and send the data.

for your problem of sending data to TabTwoVC before user click on that, your can use a variable inside the TabTwoVC and send data. and in ViewDidLoad read the data for the first time.