NSNotificationCenter 通知的使用方法详解你要知道的KVC、KVO、Delegate、Notification都在这里

//通知的名称，有时可能会使用一个方法来处理多个通知，可以根据名称区分
@property (readonly, copy) NSNotificationName name;
//通知的对象，常使用nil，如果设置了值注册的通知监听器的object需要与通知的object匹配，否则接收不到通知
@property (nullable, readonly, retain) id object;
//字典类型的用户信息，用户可将需要传递的数据放入该字典中
@property (nullable, readonly, copy) NSDictionary *userInfo;

//下面三个是NSNotification的构造函数，一般不需要手动构造
- (instancetype)initWithName:(NSNotificationName)name object:(nullable id)object userInfo:(nullable NSDictionary *)userInfo API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0)) NS_DESIGNATED_INITIALIZER;
+ (instancetype)notificationWithName:(NSNotificationName)aName object:(nullable id)anObject;
+ (instancetype)notificationWithName:(NSNotificationName)aName object:(nullable id)anObject userInfo:(nullable NSDictionary *)aUserInfo;

[NSNotificationCenter defaultCenter]

/*
注册通知监听器，只有这一个方法
observer为监听器
aSelector为接到收通知后的处理函数
aName为监听的通知的名称
object为接收通知的对象，需要与postNotification的object匹配，否则接收不到通知
*/
- (void)addObserver:(id)observer selector:(SEL)aSelector name:(nullable NSNotificationName)aName object:(nullable id)anObject;

/*
发送通知，需要手动构造一个NSNotification对象
*/
- (void)postNotification:(NSNotification *)notification;

/*
发送通知
aName为注册的通知名称
anObject为接受通知的对象，通知不传参时可使用该方法
*/
- (void)postNotificationName:(NSNotificationName)aName object:(nullable id)anObject;

/*
发送通知
aName为注册的通知名称
anObject为接受通知的对象
aUserInfo为字典类型的数据，可以传递相关数据
*/
- (void)postNotificationName:(NSNotificationName)aName object:(nullable id)anObject userInfo:(nullable NSDictionary *)aUserInfo;

/*
删除通知的监听器
*/
- (void)removeObserver:(id)observer;

/*
删除通知的监听器
aName监听的通知的名称
anObject监听的通知的发送对象
*/
- (void)removeObserver:(id)observer name:(nullable NSNotificationName)aName object:(nullable id)anObject;

/*
以block的方式注册通知监听器
*/
- (id <NSObject>)addObserverForName:(nullable NSNotificationName)name object:(nullable id)obj queue:(nullable NSOperationQueue *)queue usingBlock:(void (^)(NSNotification *note))block API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));

//ViewController部分代码

- (void)viewDidLoad
{
    //注册通知的监听器，通知名称为inputTextValueChangedNotification，处理函数为inputTextValueChangedNotificationHandler:
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(inputTextValueChangedNotificationHandler:) name:@"inputTextValueChangedNotification" object:nil];

}

//按钮点击事件处理器
- (void)buttonClicked
{
    //按钮点击后创建NextViewController并展示
    NextViewController *nvc = [[NextViewController alloc] init];
    [self presentViewController:nvc animated:YES completion:nil];
}

//通知监听器处理函数
- (void)inputTextValueChangedNotificationHandler:(NSNotification*)notification
{
    //从userInfo字典中获取数据展示到标签中
    self.label.text = notification.userInfo[@"inputText"];
}

- (void)dealloc
{
    //当ViewController销毁前删除通知监听器
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"inputTextValueChangedNotification" object:nil];
}


//NextViewController部分代码
//用户完成输入后点击按钮的事件处理器
- (void)completeButtonClickedHandler
{
    //发送通知，并构造一个userInfo的字典数据类型，将用户输入文本保存
    [[NSNotificationCenter defaultCenter] postNotificationName:@"inputTextValueChangedNotification" object:nil userInfo:@{@"inputText": self.textField.text}];
    //退出视图
    [self dismissViewControllerAnimated:YES completion:nil];
}

//NextViewController发送通知的代码修改为如下代码:
- (void)completeButtonClickedHandler
{
    //使用GCD获取一个非主线程的线程用于发送通知
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:@"inputTextValueChangedNotification" object:nil userInfo:@{@"inputText": self.textField.text}];
    });
    
    [self dismissViewControllerAnimated:YES completion:nil];
}

//ViewController通知监听器的回调函数修改为如下代码:
- (void)inputTextValueChangedNotificationHandler:(NSNotification*)notification
{
    //使用GCD获取主线程并更新UI
    dispatch_async(dispatch_get_main_queue(), ^{
        self.label.text = notification.userInfo[@"inputText"];
    });
    //如果不在主线程更新UI很有可能无法正确执行
    //self.label.text = notification.userInfo[@"inputText"];
}

#import "ViewController.h"

#define ScreenWidth [[UIScreen mainScreen] bounds].size.width
#define ScreenHeight [[UIScreen mainScreen] bounds].size.height

@interface ViewController ()

@property (nonatomic, strong) UIView *containerView;
@property (nonatomic, strong) UITextField *textField;

@end

@implementation ViewController

@synthesize containerView = _containerView;
@synthesize textField = _textField;

- (instancetype)init
{
    if (self = [super init])
    {
        self.view.backgroundColor = [UIColor whiteColor];

        //创建一个容器View可自定义相关UI
        self.containerView = [[UIView alloc] initWithFrame:CGRectMake(0, ScreenHeight - 60, ScreenWidth, 60)];
        self.containerView.backgroundColor = [UIColor redColor];
        [self.view addSubview:self.containerView];
        
        //用户输入的UITextField
        self.textField = [[UITextField alloc] initWithFrame:CGRectMake(20, 10, ScreenWidth - 40, 40)];
        self.textField.placeholder = @"input...";
        self.textField.backgroundColor = [UIColor greenColor];
        [self.containerView addSubview:self.textField];
        
        [self.view addSubview:self.containerView];
        
        //添加一个手势点击空白部分后收回键盘
        UIGestureRecognizer *gesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapView)];
        [self.view setMultipleTouchEnabled:YES];
        [self.view addGestureRecognizer:gesture];

    }
    return self;
}

- (void)viewDidLoad
{
    //注册UIKeyboardWillShowNotification通知，监听键盘弹出事件
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
    //注册UIKeyboardWillHideNotification通知，监听键盘回收事件
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
}

//自定义手势响应处理器
- (void)tapView
{
    //触发收回键盘事件
    [self.textField resignFirstResponder];
}

//UIKeyboardWillShowNotification通知回调函数
- (void)keyboardWillShow:(NSNotification*)notification
{
    //获取userInfo字典数据
    NSDictionary *userInfo = [notification userInfo];
    //根据UIKeyboardBoundsUserInfoKey键获取键盘高度
    float keyboardHeight = [[userInfo objectForKey:@"UIKeyboardBoundsUserInfoKey"] CGRectValue].size.height;
    //获取键盘弹出的动画时间
    NSTimeInterval animationDuration;
    [[userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey] getValue:&animationDuration];
    //自定义动画修改ContainerView的位置
    [UIView animateWithDuration:animationDuration animations:^{
        self.containerView.frame = CGRectMake(0, ScreenHeight - keyboardHeight - self.containerView.frame.size.height, self.containerView.frame.size.width, self.containerView.frame.size.height);
    }];

}

//UIKeyboardWillHideNotification通知回调函数
- (void)keyboardWillHide:(NSNotification*)notification
{
    //获取动画执行执行时间
    NSValue *animationDurationValue = [[notification userInfo] objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    NSTimeInterval animationDuration;
    [animationDurationValue getValue:&animationDuration];
    //自定义动画修改ContainerView的位置
    [UIView animateWithDuration:animationDuration animations:^{
        self.containerView.frame = CGRectMake(0, ScreenHeight - self.containerView.frame.size.height, self.containerView.frame.size.width, self.containerView.frame.size.height);
    }];
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];
}

@end