Sending , Listening for and Reacting to Notifications （发送，监听通知）

发送方:

//初始化通知内容  senderObject:self   userInfo:接收到通知时可从中获取到的信息

+ (instancetype)notificationWithName:(NSString *)aName object:(id)senderObject userInfo:(NSDictionary *)userInfo

//发送通知

- (void)postNotification:(NSNotification *)notification

接收方（观察者，监听者）:

//注册通知

- (void)addObserver:(id)notificationObserver selector:(SEL)notificationSelector name:(NSString *)notificationName object:(id)notificationSender

//取消通知

- (void)removeObserver:(id)notificationObserver

e.g.

======AppDelegate.h文件======

#import <UIKit/UIKit.h>

/*extern:声明全局变量（不初始化）,外部类可访问到 */

//notificationName

extern NSString *const kSetPersonInfoNotification; 

//The first-name key in the user-info dictionary of our notification 

extern NSString *const kSetPersonInfoKeyFirstName; 

// The last-name key in the user-info dictionary of our notification 

extern NSString *const kSetPersonInfoKeyLastName;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (nonatomic, strong) UIWindow *window;

@end

=======AppDelegate.m文件=====

#import "AppDelegate.h"

#import "Person.h"

NSString *const kSetPersonInfoNotification = @"SetPersonInfoNotification";

NSString *const kSetPersonInfoKeyFirstName = @"firstName";

NSString *const kSetPersonInfoKeyLastName = @"lastName";

@implementation AppDelegate

- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

    Person *steveJobs = [[Person alloc] init];   

    NSNotification *notification =

        [NSNotification  notificationWithName:kSetPersonInfoNotification

                                       object:self  //sender

                                     userInfo:@{kSetPersonInfoKeyFirstName : @"Steve",

                                                 kSetPersonInfoKeyLastName : @"Jobs"}];

    

    /* 在postNotification后，person class监听到并从notification中的userInfo中获取到了相关信息 */

   [[NSNotificationCenter defaultCenter] postNotification:notification];

    NSLog(@"Person's first name = %@", steveJobs.firstName);

    NSLog(@"Person's last name = %@", steveJobs.lastName);

    

    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    self.window.backgroundColor = [UIColor whiteColor];

    [self.window makeKeyAndVisible];

    return YES;

}

========Person.h=========

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *firstName;

@property (nonatomic, copy) NSString *lastName;

@end

========Person.m=========

#import "Person.h"

#import "AppDelegate.h"

@implementation Person

- (void) handleSetPersonInfoNotification:(NSNotification *)paramNotification{

    self.firstName =paramNotification.userInfo[kSetPersonInfoKeyFirstName];

    self.lastName = paramNotification.userInfo[kSetPersonInfoKeyLastName];   

}

//instancetype:返回类型  id:作为参数

- (instancetype) init{

    self = [super init];

    if (self != nil){       

       NSNotificationCenter *center = [NSNotificationCenter defaultCenter];

        //注册通知  addObserver必须要对应一个removeObserver，否则可能会造成内存泄漏     

        [center addObserver:self  //观察者，监听者

                  selector:@selector(handleSetPersonInfoNotification:) //接收到通知时，执行的方法，必须要有一个NSNotification参数

                      name:kSetPersonInfoNotification   //通知名称

                    object:[[UIApplication sharedApplication] delegate]];  //发送（通知）者        

    }

    return self;

}

- (void) dealloc{

    //取消注册

   [[NSNotificationCenter defaultCenter] removeObserver:self];

}

@end