How do I set up a simple delegate to communicate between two view controllers

Question

I have two UITableViewControllers and need to pass the value from the child view controller to the parent using a delegate  I know what delegates are and just wanted to see a simple to follow example   Thank You

User · Answer

Following solution is very basic and simple approach to send data from VC2 to VC1 using delegate .

PS: This solution is made in Xcode 9.X and Swift 4

Declared a protocol and created a delegate var into ViewControllerB

    import UIKit

    //Declare the Protocol into your SecondVC
    protocol DataDelegate {
        func sendData(data : String)
    }

    class ViewControllerB : UIViewController {

    //Declare the delegate property in your SecondVC
        var delegate : DataDelegate?
        var data : String = "Send data to ViewControllerA."
        override func viewDidLoad() {
            super.viewDidLoad()
        }

        @IBAction func btnSendDataPushed(_ sender: UIButton) {
                // Call the delegate method from SecondVC
                self.delegate?.sendData(data:self.data)
                dismiss(animated: true, completion: nil)
            }
        }

ViewControllerA confirms the protocol and expected to receive data via delegate method sendData

    import UIKit
        // Conform the  DataDelegate protocol in ViewControllerA
        class ViewControllerA : UIViewController , DataDelegate {
        @IBOutlet weak var dataLabel: UILabel!

        override func viewDidLoad() {
            super.viewDidLoad()
        }

        @IBAction func presentToChild(_ sender: UIButton) {
            let childVC =  UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier:"ViewControllerB") as! ViewControllerB
            //Registered delegate
            childVC.delegate = self
            self.present(childVC, animated: true, completion: nil)
        }

        // Implement the delegate method in ViewControllerA
        func sendData(data : String) {
            if data != "" {
                self.dataLabel.text = data
            }
        }
    }

User · Answer

You need to use delegates and protocols  Here is a site with an example http   iosdevelopertips com objective-c the-basics-of-protocols-and-delegates html

User · Answer

Simple example     Let s say the child view controller has a UISlider and we want to pass the value of the slider back to the parent via a delegate   In the child view controller s header file  declare the delegate type and its methods   ChildViewController h   import  lt UIKit UIKit h gt      1  Forward declaration of ChildViewControllerDelegate - this just declares    that a ChildViewControllerDelegate type exists so that we can use it    later   protocol ChildViewControllerDelegate      2  Declaration of the view controller class  as usual  interface ChildViewController   UIViewController     Delegate properties should always be weak references    See http   stackoverflow com a 4796131 263871 for the rationale     Tip  If you re not using ARC  use  assign  instead of  weak    property  nonatomic  weak  id lt ChildViewControllerDelegate gt  delegate      A simple IBAction method that I ll associate with a close button in    the UI  We ll call the delegate s childViewController didChooseValue      method inside this handler  -  IBAction handleCloseButton  id sender    end     3  Definition of the delegate s interface  protocol ChildViewControllerDelegate  lt NSObject gt   -  void childViewController  ChildViewController  viewController               didChooseValue  CGFloat value    end   In the child view controller s implementation  call the delegate methods as required   ChildViewController m   import  ChildViewController h    implementation ChildViewController  -  void handleCloseButton  id sender          Xcode will complain if we access a weak property more than         once here  since it could in theory be nilled between accesses        leading to unpredictable results  So we ll start by taking        a local  strong reference to the delegate      id lt ChildViewControllerDelegate gt  strongDelegate   self delegate          Our delegate method is optional  so we should         check that the delegate implements it     if   strongDelegate respondsToSelector  selector childViewController didChooseValue                strongDelegate childViewController self didChooseValue self slider value             end   In the parent view controller s header file  declare that it implements the ChildViewControllerDelegate protocol   RootViewController h   import  lt UIKit UIKit h gt   import  ChildViewController h    interface RootViewController   UITableViewController  lt ChildViewControllerDelegate gt    end   In the parent view controller s implementation  implement the delegate methods appropriately   RootViewController m   import  RootViewController h    implementation RootViewController  -  void tableView  UITableView   tableView didSelectRowAtIndexPath  NSIndexPath   indexPath       ChildViewController  detailViewController     ChildViewController alloc  init          Assign self as the delegate for the child view controller     detailViewController delegate   self       self navigationController pushViewController detailViewController animated YES         Implement the delegate methods for ChildViewControllerDelegate -  void childViewController  ChildViewController   viewController didChooseValue  CGFloat value           Do something with value               then dismiss the child view controller      self navigationController popViewControllerAnimated YES       end   Hope this helps

User · Answer

This below code just show the very basic use of delegate concept    you name the variable and class as per your requirement   First you need to declare a protocol   Let s call it MyFirstControllerDelegate h    protocol MyFirstControllerDelegate -  void  FunctionOne   MyDataOne   dataOne  -  void  FunctionTwo   MyDatatwo   dataTwo   end   Import MyFirstControllerDelegate h file and   confirm  your FirstController with protocol MyFirstControllerDelegate   import  MyFirstControllerDelegate h    interface FirstController   UIViewController lt MyFirstControllerDelegate gt         end   In the implementation file  you need to implement both functions of protocol    implementation FirstController        -  void  FunctionOne   MyDataOne   dataOne                     Put your finction code here             -  void  FunctionTwo   MyDatatwo   dataTwo                     Put your finction code here                 Call below function from your code     - void  CreateSecondController                     SecondController  mySecondController    SecondController alloc  initWithSomeData                        push second controller into navigation stack              mySecondController delegate   self                mySecondController release            end   in your SecondController    interface SecondController  lt UIViewController gt       id  lt MyFirstControllerDelegate gt  delegate      property  nonatomic assign   id  lt MyFirstControllerDelegate gt  delegate    end   In the implementation file of SecondController    implementation SecondController   synthesize delegate    Call below two function on self  - void  SendOneDataToFirstController       delegate FunctionOne myDataOne     - void  SendSecondDataToFirstController       delegate FunctionTwo myDataSecond       end   Here is the wiki article on delegate

[ios] How do I set up a simple delegate to communicate between two view controllers?

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