下面是一个简单的例子：
假设子视图控制器有一个UISlider，我们想通过一个代理将滑块的值传递回父视图控制器。
在子视图控制器的头文件中，声明委托类型及其方法：

• • 子视图控制器. 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 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<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

在子视图控制器的实现中，根据需要调用委托方法。

• • 子视图控制器. 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

在父视图控制器的头文件中，声明它实现ChildViewControllerDelegate协议。

• • 根视图控制器. h**

#import <UIKit/UIKit.h>
#import "ChildViewController.h"

@interface RootViewController : UITableViewController <ChildViewControllerDelegate>

@end

在父视图控制器的实现中，适当地实现委托方法。

• • 根视图控制器. 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

下面的代码只是展示了委托概念的基本用法。你可以根据自己的需要命名变量和类。
首先，您需要声明一个协议：
我们将其命名为我的第一个控制器委托。h

@protocol MyFirstControllerDelegate
- (void) FunctionOne: (MyDataOne*) dataOne;
- (void) FunctionTwo: (MyDatatwo*) dataTwo;
@end

导入MyFirstControllerDelegate.h文件并使用协议MyFirstControllerDelegate确认您的第一控制器

#import "MyFirstControllerDelegate.h"

@interface FirstController : UIViewController<MyFirstControllerDelegate>
{

}

@end

在实现文件中，需要实现协议的两个函数：

@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

在您的第二控制器中：

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

@property (nonatomic,assign)  id <MyFirstControllerDelegate> delegate;

@end

在SecondController的实现文件中。

@implementation SecondController

@synthesize delegate;
//Call below two function on self.
-(void) SendOneDataToFirstController
{
   [delegate FunctionOne:myDataOne];
}
-(void) SendSecondDataToFirstController
{
   [delegate FunctionTwo:myDataSecond];
}

@end

这是一篇关于委派的维基文章。

下面的解决方案是使用delegate将数据从VC2发送到VC1的非常基本和简单的方法。
PS：此解决方案采用Xcode 9.X和Swift 4
已声明协议并在ViewControllerB中创建了委托变量

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确认协议并预期通过委托方法sendData接收数据

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
            }
        }
    }

您需要使用委托和协议。下面是一个包含http://iosdevelopertips.com/objective-c/the-basics-of-protocols-and-delegates.html示例的站点