Access UI properties across different View Controllers in swift - ios

Question

In my app, I have a summary page which will display the summary of payers and recipients list of each payer. That is, the summary page will have a list in the left side and clicking on each list will show its details on the right side(iPad). In order to re-use the same code for iPhone version too, I have it as separate view controllers. That is, I have a base ViewController(SummaryViewController). In this i subview the ViewController of the list(SummaryListViewController) and ViewController of the details(SummaryDetailViewController). Now, when the base view controller SummaryViewController loads, i subview the list and detail view controllers like this
//ListView is a view in the base ViewController to which i subview the list ViewController
let listViewController = SummaryListViewController(nibName:"SummaryListViewController", bundle: nil)
addChildViewController(listViewController)
listViewController.view.frame = CGRect(x: 0, y: 0, width: self.ListView.frame.size.width, height: self.ListView.frame.size.height)
ListView.addSubview(listViewController.view)
listViewController.didMove(toParentViewController: self)
//DetailView is a view in the base ViewController to which i subview the Detail ViewController
let detailViewController = SummaryDetailViewController(nibName: (UIDevice.current.userInterfaceIdiom == .pad ? "SummaryDetailViewController" : "SummaryDetailViewController_iPhone"), bundle: nil)
addChildViewController(detailViewController)
DetailView.frame = CGRect(x: DetailView.frame.origin.x, y: DetailView.frame.origin.y, width: self.DetailView.frame.size.width, height: self.DetailView.frame.size.height)
DetailView.addSubview(detailViewController.view)
detailViewController.didMove(toParentViewController: self)
Now, the prob is, I have to call a method in the SummaryDetailViewController from the tableView-didSelectRow of SummaryListViewController which will update the UI elements according to the data i send.
I have tried the following things to achieve this,
I tried using addObserver in NotificationCenter. When i click on the list, i added an observer. And this observer triggers the method in the detailViewController that will update the UI elements. But this doesn't work well all the time. When i come to Summary page, go back and if i come again to summary page and do the same, the observer is called twice even after removing the observer in ViewDidDisapper. And also i learnt in few websites that NotificationCenter should not be used for this kind of a situation.
Second, Am trying to use protocols. I thought i would write a protocol in the SummaryListViewController
protocol SummaryDetailProtocol {
func setSummaryDetails()
}
class SummaryListViewController: UIViewController
{
var summaryDetailsDelegate : SummaryDetailProtocol?
func delegateFromSummaryDetails(delegate: SummaryDetailProtocol)
{
self.summaryDetailsDelegate = delegate
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)
{
self.summaryDetailsDelegate?.setSummaryDetails()
}
func delegateFromSummaryDetails(delegate: SummaryDetailProtocol)
{
self.summaryDetailsDelegate = delegate
}
}
Now in the ViewDidLoad of the SummaryDetailViewController, I would like to send the reference of the delegate to the listViewController so that the listViewController can call the setSummaryDetails method.
override func viewDidLoad()
{
super.viewDidLoad()
sendDelegateReferenceToListPage()
}
func sendDelegateReferenceToListPage()
{
let summaryListObj = SummaryListView()
//This is where the error occurs. It throws the error since i try to cast SummaryDetailViewController to parameter of type SummaryDetailProtocol of SummaryListViewController
summaryListObj.delegateFromSummaryDetails(delegate: self as! SummaryDetailProtocol)
}
Can anyone help me to get out of this

Answer 1

Protocol solution is the best. You can use like this
SummaryListViewController file:
protocol SummaryDetailProtocol {
func setSummaryDetails()
}
class SummaryListViewController: UIViewController
{
var summaryDetailsDelegate : SummaryDetailProtocol?
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)
{
self.summaryDetailsDelegate?.setSummaryDetails()//use here
}
}
SummaryDetailViewController file:
class SummaryDetailViewController: UIViewController,SummaryDetailProtocol
{
internal func setSummaryDetails() {
//return whatever you want
}
}
And finally set SummaryListViewController delegate to SummaryDetailViewController:
let detailViewController = SummaryDetailViewController(nibName: (UIDevice.current.userInterfaceIdiom == .pad ? "SummaryDetailViewController" : "SummaryDetailViewController_iPhone"), bundle: nil)
addChildViewController(detailViewController)
DetailView.frame = CGRect(x: DetailView.frame.origin.x, y: DetailView.frame.origin.y, width: self.DetailView.frame.size.width, height: self.DetailView.frame.size.height)
DetailView.addSubview(detailViewController.view)
detailViewController.didMove(toParentViewController: self)
let listViewController = SummaryListViewController(nibName:"SummaryListViewController", bundle: nil)
addChildViewController(listViewController)
listViewController.view.frame = CGRect(x: 0, y: 0, width: self.ListView.frame.size.width, height: self.ListView.frame.size.height)
ListView.addSubview(listViewController.view)
listViewController.didMove(toParentViewController: self)
listViewController.summaryDetailsDelegate = detailViewController // set delegate detail view controller