How can I pass the data from a TableViewController when I dismiss it?

Question

I have a segue from my MainViewController to my ThemesTableViewController. After performing the segue, I choose a theme on my ThemesTableViewController. When I dismiss my ThemesTableViewController, I want to see the theme selected already applied to my MainViewController. How can I achieve that?

// Here's my Theme
struct Theme {
    var name: String!
    var backgroundColor: UIColor!
    ...
}

themes = [red, blue, green]

// I have no idea how I can pass chosenTheme to my MainViewController
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    chosenTheme = themes[indexPath.row]
    dismiss(animated: true, completion: nil)
}

Answer 1

protocol ThemeDelegate {  
    func didSelectTheme(theme: Theme)  
}

var delegate: ThemeDelegate?

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {  
    chosenTheme = themes[indexPath.row]  
    self.delegate?.didSelectTheme(theme: chosenTheme)  
}

You can create a protocol and implement it like this and pass the chosenTheme to the previous viewcontroller. In your MainViewController prepare for segue function do it like this.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
    if let themeVC = segue.destination as? ThemesTableViewController {
        themeVC.delegate = self
    }
}

Also implement an extension like this in MainViewController.

extension MainViewController: ThemeDelegate {

    func didSelectTheme(theme: Theme) {
        // do something with the selected theme.
    }

}

Answer 2

Passing data with unwind segue : Passing data with unwind segue

Using NotificationCenter for applying theme after unwind : Adding dark mode to iOS app