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

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

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<MyFirstControllerDelegate>
{

}

@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:<UIViewController>
{
id <MyFirstControllerDelegate> delegate;
}

@property (nonatomic,assign) id <MyFirstControllerDelegate> 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](

[To see links please register here]

) is the wiki article on delegate.

You need to use delegates and protocols. Here is a site with an example

[To see links please register here]

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
}
}
}

Here's a 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 <UIKit/UIKit.h>

// 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

[To see links please register here]

for the rationale
// (Tip: If you're not using ARC, use `assign` instead of `weak`)
@property (nonatomic, weak) id<ChildViewControllerDelegate> 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 <NSObject>

- (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<ChildViewControllerDelegate> 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 <UIKit/UIKit.h>
#import "ChildViewController.h"

@interface RootViewController : UITableViewController <ChildViewControllerDelegate>

@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