代理传值

/**
*  代理传值 如果是多处传值，则代理传值比block方便
*/
#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

#import "AppDelegate.h"
#import "RootViewController.h"
@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.window.backgroundColor = [UIColor whiteColor];
//初始化导航控制器
UINavigationController *navi = [[UINavigationController alloc] initWithRootViewController: [[RootViewController alloc] init]];
self.window.rootViewController = navi;

[self.window makeKeyAndVisible];
return YES;
}

@end

#import <UIKit/UIKit.h>

@interface RootViewController : UIViewController

@end

#import "RootViewController.h"
#import "LFViewController.h"
@interface RootViewController ()<LFViewControllerDelegate>//导入协议

@property(nonatomic, strong) UILabel *city ;

@end

@implementation RootViewController

- (void)viewDidLoad {
[super viewDidLoad];
//添加按钮
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 100, 150, 60);
[button setTitle:@"跳到下一个页面" forState:0];
[button setBackgroundColor:[UIColor greenColor]];
[button addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];

//添加Label
self.city = [[UILabel alloc] initWithFrame:CGRectMake(100, 200, 150, 60)];
self.city.backgroundColor = [UIColor greenColor];
self.city.textAlignment = NSTextAlignmentCenter;
[self.view addSubview:self.city];
}

/**
*  按钮事件
*/
- (void)buttonAction:(UIButton*)sender{
/**
*  属性传值，从一个控制器push到下一个控制器使用属性传值比较方便
*/
LFViewController *lfController = [[LFViewController alloc] init];
lfController.delegate = self;//确定代理
[self.navigationController pushViewController:lfController animated:YES];
}

#pragma mark -- LFViewControllerDelegate --
/**
* LFViewControllerDelegate协议的方法
*
*  @param cityName 传递过来的值
*/
- (void)passCityName:(NSString *)cityName{

self.city.text = cityName;
NSLog(@"cityName: %@",cityName);
}

@end

#import <UIKit/UIKit.h>

@protocol LFViewControllerDelegate;//申明协议

@interface LFViewController : UIViewController
/**
*  防止循环引用，使用weak
*/
@property(nonatomic, weak) id<LFViewControllerDelegate> delegate;//设置代理

@end

/**
*  申请协议
*/
@protocol LFViewControllerDelegate <NSObject>
/**
*  LFViewControllerDelegate协议中的方法
*
*  @param cityName 传递的值
*/
- (void)passCityName:(NSString*)cityName;

@end

#import "LFViewController.h"

@interface LFViewController ()

@end

@implementation LFViewController

- (void)viewDidLoad {
[super viewDidLoad];
//添加按钮
UIButton *backBtn = [UIButton buttonWithType:UIButtonTypeCustom];
backBtn.frame = CGRectMake(100, 100, 150, 60);
[backBtn setTitle:@"返回且发送通知" forState:0];
[backBtn setBackgroundColor:[UIColor greenColor]];
[backBtn addTarget:self action:@selector(backBtnAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:backBtn];
}

/**
*  backBtn按钮的事件
*/
- (void)backBtnAction:(UIButton*)sender{

/**
*  如果代理能响应对应的方法，则执行该方法
*
*  @param passCityName: 方法名
*/
if ([_delegate respondsToSelector:@selector(passCityName:)]) {
[_delegate passCityName:@" London"];
[self.navigationController popViewControllerAnimated:YES];
}
}

@end