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