Passing Data between ViewController in swift4

Question

enter image description here

In this above Picture Two views are there. Top one is a view for showing date(for this view the class name is calender view) . And the bottom one is a tableview.the current view name is Main View When i am clicking on the cell of the tableview then it will go to the next view. When i am dismising the next view i want to pass some data to the calender view.How to achive this.

class MainView: UIViewController, UITableViewDataSource, UITableViewDelegate {

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

        let next = self.storyboard?.instantiateViewController(withIdentifier: "NextVC") as! NextVC
        self.present(next, animated: true, completion: nil)

    }

}


class NextVC: UIViewController {

    var sendingData: String?

    @IBAction func backAction(_ sender: Any) {
        dismiss(animated: true, completion: nil)

    }
}


class CalenderView: UIViewController{

    var receiveValue: String?
}

Here i want when i am dismissing the nextview the value of sendingData will pass to calender view.

How to do this ? Please help.

There are a few approaches. 1) You could use a global variable and set its value, so it becomes available to all view controllers. 2) Use segue to go to Calendar View, and implement override function for prepareForSegue. — NerdyGeek
– NerdyGeek, Commented Jan 13, 2019 at 20:01
Show us relation between CalendarView and other controllers. Is it some child view controller or some new view controller somewhere and how do you present it? Add this to your question. — Robert Dresler
– Robert Dresler, Commented Jan 13, 2019 at 20:07

Vlad Krupenko · Accepted Answer · 2019-01-13 20:08:46Z

I can give you two solutions:

You can create your on custom notification.

First of all on back action you should post your notification with sendingData.

NotificationCenter.default.post(name: NSNotification.Name(rawValue: UpdateCalendarNotification), object: sendingData)

Next, on main view controller with calendar view you should register notification for "UpdateCalendarNotification" name.

    func registerNotifications() {
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(updateCalendarView(_:)),
                                               name: NSNotification.Name(rawValue: "UpdateCalendarNotification"),
                                               object: nil)
    }

And on selector updateCalendarView(_:) you should handle changes for calendar view.

    @objc
    func updateCalendarView(_ notification: NSNotification) {
        if let sendingData = notification.object as? String {
            /// Update calendar view
        }
    }

Second solution is public block for you "next controller".

On next view controller you should add this handler:

    var onDismiss: ((String?) -> Void)?

and in backAction method you should pass your data

    onDismiss?(sendingData)

In your main view controller you should implement this block like this:

let next = self.storyboard?.instantiateViewController(withIdentifier: "NextVC") as! NextVC
next.onDismiss = { [weak self] (sendingData) in
    self?.calendarView.receiveValue = sendingData
}
self.present(next, animated: true, completion: nil)

I hope this will help you)

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