ReactiveObjC简介

最正确的方式要从读官方文档ReactiveObjc 开始

ReactiveObjC 是一个函数式响应式编程框架(functional reactive programming)，不是Rx系列的。
Rx系列只是一种函数响应式的扩展，相比就很轻量。目前iOS的Rx系列只有RxSwift，需要单独学习😊

为啥要用它？

它提供了统一的方法来处理异步行为^[1]。

常用的几种方式：delegate、target-action、NSNotificationCenter、KVO、blcok

1、delegate
比如要实时监听输入框的文字，限制字数、校验邮箱等等操作

• 传统写法

@interface ViewController ()< UITextFieldDelegate >
...
self.textField.delegate = self;

...
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
 // 处理逻辑
}

• RAC写法

[[self.textField rac_textSignal] subscribeNext:^(NSString * _Nullable x) {
        NSLog(@"textfield.text -- %@",x);
 }];

2、target-action
常用与Button的点击事件

• 传统写法

[self.btn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
...
- (void)btnClick:(UIButton *)btn{
    // 处理点击事件
}

• RAC写法

[[self.btn rac_signalForControlEvents:(UIControlEventTouchUpInside)] subscribeNext:^(__kindof UIControl * _Nullable x) {
        // 处理点击事件
 }];

3、NSNotificationCenter & KVO

• 传统写法

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];
...
- (void)didEnterBackground{
    // 处理事件
}
// KVO
static void *ObservationContext = &ObservationContext;
[LoginManager.sharedManager addObserver:self forKeyPath:@"loggingIn" options:NSKeyValueObservingOptionInitial context:&ObservationContext];
...
- (void)dealloc {
    [LoginManager.sharedManager removeObserver:self forKeyPath:@"loggingIn" context:ObservationContext];
    [NSNotificationCenter.defaultCenter removeObserver:self];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if (context == ObservationContext) {
        // 处理事件
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

• RAC写法

[[[NSNotificationCenter defaultCenter] rac_addObserverForName:UIApplicationDidEnterBackgroundNotification object:nil] subscribeNext:^(NSNotification * _Nullable x) {
      // 处理事件
 }];

// KVO
[RACObserve(LoginManager.sharedManager, loggingIn) subscribeNext:^(id  _Nullable x) {
    // 处理事件
}];

4、Block
例如AFNetworking网络请求成功、失败，往往都以block作为参数实现。

• 传统写法

AFHTTPSessionManager *sessionManager = [AFHTTPSessionManager manager];
[sessionManager GET:@"url" parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
        
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        
 }];

• RAC写法
  先创建继承 AFHTTPSessionManager，用单例操作

- (RACSignal *)signalGet:(NSString *)url param:(id)param{
   // 返回信号量
    return [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber>  _Nonnull subscriber) {
        // 内部调用GET方法
        [self GET:url parameters:param progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
            [subscriber sendNext:responseObject];
            [subscriber sendCompleted];
            
        } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
            [subscriber sendError:error];
        }];
        return nil;
    }];
}

...

[[[RACHttpManager shareRACHttpManager] signalGet:@"url" param:nil] subscribeNext:^(id  _Nullable x) {
    // 成功的信号
} error:^(NSError * _Nullable error) {
     // 失败的信号 
 }];

感觉差别不大😁，那是因为还没有深入的讲到信号量的作用，以及文档中反复提到的futures and promises^[2]概念，掘金翻译的这篇文章很好的解释了。

怎么集成

可以在Cocoapods搜索ReactiveObjC看下

pod 'ReactiveObjC'

---

1. ReactiveObjc 简介中出现这句 "One of the major advantages of RAC is that it provides a single, unified approach to dealing with asynchronous behaviors, including delegate methods, callback blocks, target-action mechanisms, notifications, and KVO." ↩

2. ReactiveObjc 讲异步操作嵌套的解决办法中提到 "Signals can be chained to sequentially execute asynchronous operations, instead of nesting callbacks with blocks. This is similar to how futures and promises are usually used:
   "cf ↩