快速访问不同View Controller中的UI属性

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,

1. 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.

2. 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