舉個(gè)例子：

// 命令式
function mysteryFn (nums) {
  let squares = []
  let sum = 0                           // 1. 創(chuàng)建中間變量

  for (let i = 0; i < nums.length; i++) {
    squares.push(nums[i] * nums[i])     // 2. 循環(huán)計(jì)算平方
  }

  for (let i = 0; i < squares.length; i++) {
    sum += squares[i]                   // 3. 循環(huán)累加
  }

  return sum
}

// 以上代碼都是 how 而不是 what...
// 函數(shù)式
const mysteryFn = (nums) => nums
  .map(x => x * x)                      // a. 平方
  .reduce((acc, cur) => acc + cur, 0)   // b. 累加

響應(yīng)式

什么是響應(yīng)式拆挥？這個(gè)問題其實(shí)之前有篇里面我也講過薄霜，就是如果正常我們寫一行代碼a = b + c，此時(shí)如果b和c都是1纸兔，那么這個(gè)時(shí)候a得到的就是2惰瓜，然后如果在這行之后b變?yōu)榱?，你需要重新執(zhí)行a = b + c才能讓a更新為3汉矿，但是響應(yīng)式就是當(dāng)b變?yōu)?的時(shí)候c自動(dòng)就可以變成3崎坊。

RAC使用

強(qiáng)推：http://www.reibang.com/p/35a28cf0a22f

終于到了真正的使用啦，每個(gè)類都大概看一下怎么用吧~ RAC有現(xiàn)成的KVO以及UI之類的方法洲拇，可以直接用例如：

[[button1 rac_signalForControlEvents:UIControlEventTouchUpInside] subscribeNext:^(__kindof UIControl * _Nullable x) {
  NSLog(@"button1 clicked");
}];

1. RACSignal

高階用法歡迎參考：http://www.reibang.com/p/7620edadcf88

- (void)testSignal {
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        
        NSLog(@"block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)奈揍，就會(huì)調(diào)用block。");
        
        // 2.發(fā)送信號(hào)
//        [subscriber sendNext:@1];
        
        // 如果不在發(fā)送數(shù)據(jù)赋续，最好發(fā)送信號(hào)完成打月，內(nèi)部會(huì)自動(dòng)調(diào)用[RACDisposable disposable]取消訂閱信號(hào)。
        [subscriber sendError:nil];
        
        return [RACDisposable disposableWithBlock:^{
            NSLog(@"信號(hào)被銷毀");
        }];
    }];
    
    [signal subscribeNext:^(id  _Nullable x) {
        NSLog(@"signal touched 1");
    }];
    
    [signal subscribeNext:^(id  _Nullable x) {
        NSLog(@"signal touched 2");
    }];
}

上面醬紫如果只是設(shè)置了訂閱block蚕捉，外加signal在函數(shù)結(jié)束的時(shí)候沒有引用了就會(huì)自動(dòng)銷毀，于是輸出為：

2020-08-21 23:31:04.311701+0800 Example1[98032:2252660] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)柴淘，就會(huì)調(diào)用block迫淹。
2020-08-21 23:31:04.311879+0800 Example1[98032:2252660] 信號(hào)被銷毀
2020-08-21 23:31:04.312061+0800 Example1[98032:2252660] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)秘通，就會(huì)調(diào)用block。
2020-08-21 23:31:04.312176+0800 Example1[98032:2252660] 信號(hào)被銷毀

這里的信號(hào)被銷毀每次subscribe的時(shí)候都會(huì)調(diào)用敛熬，其實(shí)也就是signal可能對(duì)應(yīng)多個(gè)訂閱者肺稀，默認(rèn)每個(gè)訂閱者加入的時(shí)候給signal一個(gè)機(jī)會(huì)讓它在block里面給訂閱者發(fā)消息，如果它發(fā)了应民，訂閱者的next block就會(huì)執(zhí)行话原，但無(wú)論發(fā)了沒有，默認(rèn)都是給signal處理機(jī)會(huì)以后就會(huì)執(zhí)行RACDisposable dispose解除已經(jīng)有過接手信號(hào)機(jī)會(huì)的訂閱者诲锹。

現(xiàn)在打開[subscriber sendNext:@1];的注釋繁仁，那么由于調(diào)用了sendNext，訂閱者的訂閱block就會(huì)被調(diào)用归园，所以signal會(huì)被touch~

2020-08-21 23:34:32.705363+0800 Example1[98144:2256354] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)黄虱，就會(huì)調(diào)用block。
2020-08-21 23:34:32.705608+0800 Example1[98144:2256354] signal touched 1
2020-08-21 23:34:32.705818+0800 Example1[98144:2256354] 信號(hào)被銷毀
2020-08-21 23:34:32.706005+0800 Example1[98144:2256354] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)庸诱，就會(huì)調(diào)用block捻浦。
2020-08-21 23:34:32.706165+0800 Example1[98144:2256354] signal touched 2
2020-08-21 23:34:32.706355+0800 Example1[98144:2256354] 信號(hào)被銷毀

原理可以參考上面的系列文章里面的第一個(gè)，主要是醬紫的：

signal原理

每個(gè)subscriber都遵循RACSubscriber協(xié)議桥爽，其實(shí)有4個(gè)方法：

- (void)sendNext:(nullable id)value;
- (void)sendError:(nullable NSError *)error;
- (void)sendCompleted;
- (void)didSubscribeWithDisposable:(RACCompoundDisposable *)disposable;

error和complete其實(shí)對(duì)應(yīng)著我們?cè)谟嗛喌臅r(shí)候傳入的block朱灿，如果我們send error了，那么error的block就會(huì)執(zhí)行钠四，complete也是：

RACDisposable *dispose = [signal subscribeNext:^(id  _Nullable x) {
    NSLog(@"signal touched 1");
} error:^(NSError * _Nullable error) {
    NSLog(@"signal error");
} completed:^{
    NSLog(@"signal completed");
}];

2. RACDisposable

這個(gè)就是聽起來(lái)就知道是做什么系列了盗扒，其實(shí)是訂閱者銷毀的時(shí)候回觸發(fā)的block，RACDisposable就是對(duì)block的一層包裝：

- (instancetype)initWithBlock:(void (^)(void))block {
    NSCParameterAssert(block != nil);

    self = [super init];

    _disposeBlock = (void *)CFBridgingRetain([block copy]); 
    OSMemoryBarrier();

    return self;
}

訂閱者取消訂閱有兩種可能性都會(huì)觸發(fā)：

1. 訂閱者destroy沒有強(qiáng)引用了
2. 手動(dòng)調(diào)用了[disposable dispose]

第一種其實(shí)就是為什么我們的signal每次被訂閱都會(huì)銷毀一次形导，我們?nèi)绻靡粋€(gè)數(shù)組持有一下訂閱者环疼，那么就不會(huì)觸發(fā)銷毀啦：

- (void)testSignal {
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        
        NSLog(@"block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)，就會(huì)調(diào)用block朵耕。");
        
        // 2.發(fā)送信號(hào)
        [subscriber sendNext:@1];
        
        [self->subscribers addObject:subscriber];
        
        return [RACDisposable disposableWithBlock:^{
            NSLog(@"信號(hào)被銷毀");
        }];
    }];
    
    RACDisposable *dispose = [signal subscribeNext:^(id  _Nullable x) {
        NSLog(@"signal touched 1");
    } error:^(NSError * _Nullable error) {
        NSLog(@"signal error");
    } completed:^{
        NSLog(@"signal completed");
    }];
//    [dispose dispose];
    
    [signal subscribeNext:^(id  _Nullable x) {
        NSLog(@"signal touched 2");
    }];
}

輸出：
2020-08-22 12:46:15.780694+0800 Example1[3545:41194] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)炫隶，就會(huì)調(diào)用block。
2020-08-22 12:46:15.780933+0800 Example1[3545:41194] signal touched 1
2020-08-22 12:46:15.781115+0800 Example1[3545:41194] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)阎曹，就會(huì)調(diào)用block伪阶。
2020-08-22 12:46:15.781244+0800 Example1[3545:41194] signal touched 2

這個(gè)時(shí)候就發(fā)現(xiàn)dispose沒有再調(diào)用了~ 那么如果我想讓他不通過釋放訂閱者解除訂閱要怎么做呢？打開上面注釋的[dispose dispose];即可手動(dòng)釋放訂閱者处嫌，輸出將變?yōu)椋?/p>

2020-08-22 12:48:55.519454+0800 Example1[3626:43490] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)栅贴，就會(huì)調(diào)用block。
2020-08-22 12:48:55.519770+0800 Example1[3626:43490] signal touched 1
2020-08-22 12:48:55.519971+0800 Example1[3626:43490] 信號(hào)被銷毀
2020-08-22 12:48:55.520135+0800 Example1[3626:43490] block調(diào)用時(shí)刻：每當(dāng)有訂閱者訂閱信號(hào)熏迹，就會(huì)調(diào)用block檐薯。
2020-08-22 12:48:55.520283+0800 Example1[3626:43490] signal touched 2

注意哦，如果我們sendNext以后調(diào)用了sendComplete，那么其實(shí)sendComplete里面會(huì)給你調(diào)用dispose方法解除訂閱噠坛缕。

3. RACSubject

這個(gè)RACSubject其實(shí)是繼承自RACSignal的墓猎，它更像我們以為的信號(hào)，就是當(dāng) send next 觸發(fā)的時(shí)候赚楚，所有訂閱者的next block都會(huì)被觸發(fā)：

- (void)testSubject {
    RACSubject *subject = [RACSubject subject];
    [subject subscribeNext:^(id  _Nullable x) {
        NSLog(@"next1 :%@", x);
    }];
    
    [subject subscribeNext:^(id  _Nullable x) {
        NSLog(@"next2 :%@", x);
    }];
    
    NSLog(@"testSubject");
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [subject sendNext:@"x"];
    });
}

輸出：
2020-08-22 12:52:43.338328+0800 Example1[3713:45879] testSubject
2020-08-22 12:52:46.338972+0800 Example1[3713:45879] next1 :x
2020-08-22 12:52:46.339484+0800 Example1[3713:45879] next2 :x

原理其實(shí)就是它循環(huán)了一下所有的訂閱者：

- (void)sendNext:(id)value {
    [self enumerateSubscribersUsingBlock:^(id<RACSubscriber> subscriber) {
        [subscriber sendNext:value];
    }];
}

那么如果我想dispose一下腫么破呢毙沾？那就要看subscriber協(xié)議里面最后一個(gè)方法了：

- (void)testSubject {
    RACSubject *subject = [RACSubject subject];
    [subject subscribeNext:^(id  _Nullable x) {
        NSLog(@"next1 :%@", x);
    }];
    
    [subject didSubscribeWithDisposable:[RACCompoundDisposable disposableWithBlock:^{
        NSLog(@"disposable block1");
    }]];

    [subject didSubscribeWithDisposable:[RACCompoundDisposable disposableWithBlock:^{
        NSLog(@"disposable block2");
    }]];
    
    [subject subscribeNext:^(id  _Nullable x) {
        NSLog(@"next2 :%@", x);
    }];
    
    NSLog(@"testSubject");
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [subject sendNext:@"x"];
    });
}

輸出：
2020-08-22 12:53:56.902050+0800 Example1[4259:50201] testSubject
2020-08-22 12:53:59.902840+0800 Example1[4259:50201] next1 :x
2020-08-22 12:53:59.903351+0800 Example1[4259:50201] next2 :x
2020-08-22 12:53:59.903802+0800 Example1[4259:50201] disposable block1
2020-08-22 12:53:59.904165+0800 Example1[4259:50201] disposable block2

也就是在signal銷毀的時(shí)候會(huì)觸發(fā)我們加入的disposable們，并且是按照加入的順序觸發(fā)噠宠页。

4. RACReplaySubject

這個(gè)其實(shí)和subject很類似左胞，區(qū)別就是這個(gè)是可以先發(fā)信號(hào)再訂閱，也就是新的訂閱者訂閱的時(shí)候举户，可以拿到之前發(fā)過的所有歷史信息：

- (void)testReplaySubject {
    RACReplaySubject *subject = [RACReplaySubject subject];
    [subject sendNext:@"hhh1"];
    [subject sendNext:@"hhh2"];
    [subject subscribeNext:^(id  _Nullable x) {
        NSLog(@"value received: %@", x);
    }];
    NSLog(@"finished");
}

輸出：
2020-08-22 12:57:29.315784+0800 Example1[4367:53504] value received: hhh1
2020-08-22 12:57:29.316010+0800 Example1[4367:53504] value received: hhh2
2020-08-22 12:57:29.316146+0800 Example1[4367:53504] finished

這個(gè)原理其實(shí)就是在sendNext的時(shí)候把數(shù)據(jù)存到了一個(gè)數(shù)組里面烤宙，然后訂閱者訂閱的時(shí)候會(huì)先把這個(gè)數(shù)組遍歷一次：

- (void)sendNext:(id)value {
    @synchronized (self) {
        [self.valuesReceived addObject:value ?: RACTupleNil.tupleNil];
        
        if (self.capacity != RACReplaySubjectUnlimitedCapacity && self.valuesReceived.count > self.capacity) {
            [self.valuesReceived removeObjectsInRange:NSMakeRange(0, self.valuesReceived.count - self.capacity)];
        }
        
        [super sendNext:value];
    }
}

- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
    RACCompoundDisposable *compoundDisposable = [RACCompoundDisposable compoundDisposable];

    RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
        @synchronized (self) {
            for (id value in self.valuesReceived) {
                if (compoundDisposable.disposed) return;

                [subscriber sendNext:(value == RACTupleNil.tupleNil ? nil : value)];
            }

            ……
        }
    }];

    [compoundDisposable addDisposable:schedulingDisposable];

    return compoundDisposable;
}

5. RACScheduler

Scheduler其實(shí)是對(duì)GCD的一個(gè)封裝，主要是做調(diào)度的：

- (void)testScheduler {
    NSLog(@"started");
    [[RACScheduler scheduler] schedule:^{
        NSLog(@"當(dāng)前線程:%@",[NSThread currentThread]);
    }];
    NSLog(@"finished");
}

輸出：
2020-08-22 13:02:05.910901+0800 Example1[4478:57139] started
2020-08-22 13:02:05.911190+0800 Example1[4478:57139] finished
2020-08-22 13:02:05.911413+0800 Example1[4478:57289] 當(dāng)前線程:<NSThread: 0x600001200d80>{number = 3, name = (null)}

RACScheduler是一個(gè)父類敛摘，他有很多子類：

RACScheduler的子類

我們用到的直接其實(shí)是：

+ (RACScheduler *)schedulerWithPriority:(RACSchedulerPriority)priority name:(NSString *)name {
    return [[RACTargetQueueScheduler alloc] initWithName:name targetQueue:dispatch_get_global_queue(priority, 0)];
}

@interface RACTargetQueueScheduler : RACQueueScheduler

看RACQueueScheduler的名字也可以知道這個(gè)scheduler其實(shí)是一個(gè)依賴于queue執(zhí)行的：

- (RACDisposable *)schedule:(void (^)(void))block {
    NSCParameterAssert(block != NULL);

    RACDisposable *disposable = [[RACDisposable alloc] init];

    dispatch_async(self.queue, ^{
        if (disposable.disposed) return;
        [self performAsCurrentScheduler:block];
    });

    return disposable;
}

也就是說门烂，它的執(zhí)行順序依賴于我們傳入的是并行還是串行queue。

我們通過[RACScheduler scheduler]創(chuàng)建的其實(shí)傳入的是global queue兄淫，也就是一個(gè)并行的隊(duì)列屯远，下面來(lái)嘗試一下：

- (void)testScheduler {
    NSLog(@"started");
    [[RACScheduler scheduler] schedule:^{
        NSLog(@"當(dāng)前線程1:%@",[NSThread currentThread]);
        sleep(3);
        NSLog(@"當(dāng)前線程1:%@",[NSThread currentThread]);
    }];
    
    [[RACScheduler scheduler] schedule:^{
        NSLog(@"當(dāng)前線程2:%@",[NSThread currentThread]);
        sleep(3);
        NSLog(@"當(dāng)前線程2:%@",[NSThread currentThread]);
    }];
    
    NSLog(@"finished");
}

輸出：
2020-08-22 13:09:57.205527+0800 Example1[4663:63879] started
2020-08-22 13:09:57.205864+0800 Example1[4663:63879] finished
2020-08-22 13:09:57.206289+0800 Example1[4663:63989] 當(dāng)前線程1:<NSThread: 0x6000035a4640>{number = 4, name = (null)}
2020-08-22 13:09:57.206331+0800 Example1[4663:63988] 當(dāng)前線程2:<NSThread: 0x6000035f07c0>{number = 5, name = (null)}
2020-08-22 13:10:00.207777+0800 Example1[4663:63989] 當(dāng)前線程1:<NSThread: 0x6000035a4640>{number = 4, name = (null)}
2020-08-22 13:10:00.207825+0800 Example1[4663:63988] 當(dāng)前線程2:<NSThread: 0x6000035f07c0>{number = 5, name = (null)}

RACScheduler還有其他的獲取方式：

• immediateScheduler，立即執(zhí)行的線程捕虽，其實(shí)就是在當(dāng)前線程執(zhí)行的
• mainThreadScheduler慨丐，獲取主線程調(diào)度器
• currentScheduler，就是獲取當(dāng)前線程調(diào)度器泄私，但不會(huì)立即執(zhí)行

- (void)testScheduler {
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"當(dāng)前線程:%@",[NSThread currentThread]);
        
        NSLog(@"started");
        [[RACScheduler immediateScheduler] schedule:^{
            NSLog(@"當(dāng)前線程2:%@",[NSThread currentThread]);
            sleep(3);
            NSLog(@"當(dāng)前線程2:%@",[NSThread currentThread]);
        }];
        
        NSLog(@"finished");
    });
}

輸出：
2020-08-22 21:26:46.562790+0800 Example1[7651:88680] started
2020-08-22 21:26:46.563918+0800 Example1[7651:88742] 當(dāng)前線程:<NSThread: 0x6000038905c0>{number = 7, name = (null)}
2020-08-22 21:26:46.564143+0800 Example1[7651:88742] started
2020-08-22 21:26:46.564534+0800 Example1[7651:88742] 當(dāng)前線程2:<NSThread: 0x6000038905c0>{number = 7, name = (null)}
2020-08-22 21:26:49.569298+0800 Example1[7651:88742] 當(dāng)前線程2:<NSThread: 0x6000038905c0>{number = 7, name = (null)}
2020-08-22 21:26:49.569719+0800 Example1[7651:88742] finished

如果換成mainThreadScheduler輸出就會(huì)是醬紫房揭，不再是同步調(diào)用啦：

2020-08-22 21:29:35.556247+0800 Example1[7754:91485] 當(dāng)前線程:<NSThread: 0x600000b249c0>{number = 4, name = (null)}
2020-08-22 21:29:35.556581+0800 Example1[7754:91485] started
2020-08-22 21:29:35.556826+0800 Example1[7754:91485] finished
2020-08-22 21:29:35.579004+0800 Example1[7754:91405] 當(dāng)前線程2:<NSThread: 0x600000b61080>{number = 1, name = main}
2020-08-22 21:29:38.579679+0800 Example1[7754:91405] 當(dāng)前線程2:<NSThread: 0x600000b61080>{number = 1, name = main}

如果換成currentScheduler是醬紫的，按理說也是異步的晌端，但實(shí)際輸出是醬紫的：

2020-08-22 21:31:23.592051+0800 Example1[7841:93828] 當(dāng)前線程:<NSThread: 0x60000340dfc0>{number = 5, name = (null)}
2020-08-22 21:31:23.592302+0800 Example1[7841:93828] started
2020-08-22 21:31:23.592497+0800 Example1[7841:93828] finished

為啥沒執(zhí)行schedule的內(nèi)容呢捅暴？

+ (RACScheduler *)currentScheduler {
    RACScheduler *scheduler = NSThread.currentThread.threadDictionary[RACSchedulerCurrentSchedulerKey];
    if (scheduler != nil) return scheduler;
    if ([self.class isOnMainThread]) return RACScheduler.mainThreadScheduler;

    return nil;
}

如果當(dāng)前線程之前沒有創(chuàng)建scheduler并且又不是主線程，那么就會(huì)return一個(gè)nil咧纠，自然就不會(huì)執(zhí)行啦蓬痒。

• scheduler還可以通過優(yōu)先級(jí)來(lái)創(chuàng)建，例如醬紫：

- (void)testScheduler {
    [[RACScheduler schedulerWithPriority:RACSchedulerPriorityLow] schedule:^{
        NSLog(@"scheduler:%@",[RACScheduler currentScheduler]);
        NSLog(@"當(dāng)前線程:%@",[NSThread currentThread]);
    }];
}

輸出：
2020-08-22 21:35:24.544379+0800 Example1[8014:98226] scheduler:<RACTargetQueueScheduler: 0x600001476a20> org.reactivecocoa.ReactiveObjC.RACScheduler.backgroundScheduler
2020-08-22 21:35:24.544993+0800 Example1[8014:98226] 當(dāng)前線程:<NSThread: 0x600000167900>{number = 5, name = (null)}

RAC優(yōu)先級(jí)其實(shí)是對(duì)應(yīng)GCD的優(yōu)先級(jí)的：

typedef enum : long {
    RACSchedulerPriorityHigh = DISPATCH_QUEUE_PRIORITY_HIGH,
    RACSchedulerPriorityDefault = DISPATCH_QUEUE_PRIORITY_DEFAULT,
    RACSchedulerPriorityLow = DISPATCH_QUEUE_PRIORITY_LOW,
    RACSchedulerPriorityBackground = DISPATCH_QUEUE_PRIORITY_BACKGROUND,
} RACSchedulerPriority;

不同優(yōu)先級(jí)其實(shí)就是對(duì)應(yīng)了gcd不同的queue漆羔，注意這里默認(rèn)是global的queue哈：

+ (RACScheduler *)schedulerWithPriority:(RACSchedulerPriority)priority name:(NSString *)name {
    return [[RACTargetQueueScheduler alloc] initWithName:name targetQueue:dispatch_get_global_queue(priority, 0)];
}

Finally梧奢，為什么RAC要封裝GCD呢？這個(gè)其實(shí)我感覺是為了更好用和好看演痒，dispatch很多縮進(jìn)亲轨，但是RAC如果可以直接delivery就會(huì)好看很多~ 希望有大佬來(lái)教學(xué)一下這個(gè)問題~

6. RACMulticastConnection

如果我們通過signal做網(wǎng)絡(luò)請(qǐng)求可以醬紫：

- (void)testConn {
    RACSignal * signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        NSLog(@"發(fā)送網(wǎng)絡(luò)請(qǐng)求");
        sleep(3);
        [subscriber sendNext:@"得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)"];
        
        return nil;
    }];
    
    [signal subscribeNext:^(id x) {
        NSLog(@"1 - %@",x);
    }];
    
    [signal subscribeNext:^(id x) {
        NSLog(@"2 - %@",x);
    }];
    
    [signal subscribeNext:^(id x) {
        NSLog(@"3 - %@",x);
    }];
}

輸出：
2020-08-22 21:46:45.095715+0800 Example1[8973:108249] 發(fā)送網(wǎng)絡(luò)請(qǐng)求
2020-08-22 21:46:48.097432+0800 Example1[8973:108249] 1 - 得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)
2020-08-22 21:46:48.098200+0800 Example1[8973:108249] 發(fā)送網(wǎng)絡(luò)請(qǐng)求
2020-08-22 21:46:51.099029+0800 Example1[8973:108249] 2 - 得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)
2020-08-22 21:46:51.099650+0800 Example1[8973:108249] 發(fā)送網(wǎng)絡(luò)請(qǐng)求
2020-08-22 21:46:54.101352+0800 Example1[8973:108249] 3 - 得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)

就可能會(huì)重復(fù)觸發(fā)，RACMulticastConnection就是用于避免這個(gè)事兒的：

- (void)testConn {
    RACSignal * signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        NSLog(@"發(fā)送網(wǎng)絡(luò)請(qǐng)求");
        sleep(3);
        
        [subscriber sendNext:@"得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)"];
        
        return nil;
    }];
    
    RACMulticastConnection *connect = [signal publish];
    
    [connect.signal subscribeNext:^(id x) {
        NSLog(@"1 - %@",x);
    }];
    
    [connect.signal subscribeNext:^(id x) {
        NSLog(@"2 - %@",x);
    }];
    
    [connect.signal subscribeNext:^(id x) {
        NSLog(@"3 - %@",x);
    }];
    
    [connect connect];
}

輸出：

2020-08-22 21:57:56.231520+0800 Example1[9697:117688] 發(fā)送網(wǎng)絡(luò)請(qǐng)求
2020-08-22 21:57:59.232046+0800 Example1[9697:117688] 1 - 得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)
2020-08-22 21:57:59.232525+0800 Example1[9697:117688] 2 - 得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)
2020-08-22 21:57:59.232854+0800 Example1[9697:117688] 3 - 得到網(wǎng)絡(luò)請(qǐng)求數(shù)據(jù)

它的大概原理是醬紫的鸟顺，感興趣的可以看之前的參考：

conn原理

其實(shí)就是conn的signal其實(shí)是一個(gè)subject惦蚊，而非之前的RACSignal，所以可以訂閱好幾個(gè)。注意哦蹦锋，signal訂閱的時(shí)候是順序執(zhí)行的曾撤，需要先執(zhí)行創(chuàng)建時(shí)候每次訂閱觸發(fā)的block，之后才能走下一個(gè)訂閱晕粪；而subject比較正常，是可以先訂閱的渐裸，然后一起等待sendNext的觸發(fā)

7. RACCommand

這個(gè)東西其實(shí)我也一直很迷茫是干啥用的~ 參考了：http://www.reibang.com/p/dc472c644e7b

一般情況下巫湘，RACCommand主要用來(lái)封裝一些請(qǐng)求、事件等昏鹃，舉個(gè)例子尚氛，我們的tableView在下拉滾動(dòng)時(shí)若想刷新數(shù)據(jù)需要向接口提供頁(yè)碼或者最后一個(gè)數(shù)據(jù)的ID，我們可以把請(qǐng)求封裝進(jìn)RACCommand里洞渤，想要獲取數(shù)據(jù)的時(shí)候只要將頁(yè)碼或者ID傳入RACCommand里就可以了阅嘶，同時(shí)監(jiān)控RACCommand何時(shí)完成,若完成后將數(shù)據(jù)加入到tableview的數(shù)組就可以了，這是一個(gè)平常用的比較多的場(chǎng)景载迄。使用是主要有三個(gè)注意點(diǎn)：

1. RACCommand必須返回信號(hào),信號(hào)可以為空
2. RACCommand必須強(qiáng)引用
3. RACCommand發(fā)送完數(shù)據(jù)必須發(fā)送完成信號(hào)

例如醬紫：

-(void)loadInfo{

      //input就是控制器中,viewmodel執(zhí)行command時(shí)excute傳入的參數(shù)
      RACCommand * command = [[RACCommand alloc]initWithSignalBlock:^RACSignal *(id input) {

          //command必須有信號(hào)返回值,如果沒有的話可以為[RACSignal empty]
          return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber)
                  {
                      NSMutableDictionary * params = [NSMutableDictionary dictionary];

                      params[@"build"] = @"3360";
                      params[@"channel"] = @"appstore";
                      params[@"plat"] = @"2";

                      [FYRequestTool GET:@"http://app.bilibili.com/x/banner" parameters:params progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {

                          [subscriber sendNext:responseObject];

                          //發(fā)送完信號(hào)必須發(fā)送完成信號(hào),否則無(wú)法執(zhí)行
                          [subscriber sendCompleted];

                      } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {

                          [subscriber sendError:error];

                      }];

                  return [RACDisposable disposableWithBlock:^{

                          [FYRequestTool cancel];

                          NSLog(@"這里面可以寫取消請(qǐng)求,完成信號(hào)后請(qǐng)求會(huì)取消");

                          }];
                  }];
          }];

      //必須強(qiáng)引用這個(gè)command,否則無(wú)法執(zhí)行
      self.command = command;
  }

signal如果我們?cè)谟嗛喌腷lock里面去做網(wǎng)絡(luò)請(qǐng)求讯柔，是無(wú)法帶入一些參數(shù)給它的，但是command可以通過execute的參數(shù)做區(qū)分护昧，然后你可以返回一個(gè)signal魂迄，在signal內(nèi)部通過不同input做不同的事情，最后sendNext一下觸發(fā)訂閱者的block告知訂閱者并返回拿到的數(shù)據(jù)：

- (void)testCommand {
    RACCommand *command = [[RACCommand alloc] initWithSignalBlock:^RACSignal * _Nonnull(id  _Nullable input) {
        NSLog(@"create command 1 with input:%@", input);
        sleep(3);
        NSLog(@"create command 2");
        
        return [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber>  _Nonnull subscriber) {
            // 這里可以拿input去做不同的事情
            NSLog(@"signal subscribed 1 with input:%@", input);
            sleep(3);
            [subscriber sendNext:@"a"];
            NSLog(@"signal subscribed 2");
            
            return [RACDisposable disposableWithBlock:^{
                NSLog(@"RACDisposable disposable block");
            }];
        }];
    }];
    
    NSLog(@"testCommand");
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        
        NSString *input = @"執(zhí)行";
        
        [[command.executionSignals switchToLatest] subscribeNext:^(id  _Nullable x) {
            NSLog(@"switchToLatest-->%@",x);
        }];
        
        [command execute:input];
    });
}

輸出：
2020-08-22 22:25:33.442545+0800 Example1[10798:139387] testCommand
2020-08-22 22:25:36.443640+0800 Example1[10798:139387] create command 1 with input:執(zhí)行
2020-08-22 22:25:39.445241+0800 Example1[10798:139387] create command 2
2020-08-22 22:25:39.447601+0800 Example1[10798:139387] executing-->0
2020-08-22 22:25:39.448927+0800 Example1[10798:139387] executing-->1
2020-08-22 22:25:39.449554+0800 Example1[10798:139387] signal subscribed 1 with input:執(zhí)行
2020-08-22 22:25:42.450867+0800 Example1[10798:139387] switchToLatest-->a
2020-08-22 22:25:42.451391+0800 Example1[10798:139387] signal subscribed 2
2020-08-22 22:25:42.451810+0800 Example1[10798:139387] RACDisposable disposable block

8. bind

bind其實(shí)是RACStream的方法惋耙，但是很多類都復(fù)寫了它捣炬，例如signal的：

- (RACSignal *)bind:(RACSignalBindBlock (^)(void))block {
    NSCParameterAssert(block != NULL);

    /*
     * -bind: should:
     * 
     * 1. Subscribe to the original signal of values.
     * 2. Any time the original signal sends a value, transform it using the binding block.
     * 3. If the binding block returns a signal, subscribe to it, and pass all of its values through to the subscriber as they're received.
     * 4. If the binding block asks the bind to terminate, complete the _original_ signal.
     * 5. When _all_ signals complete, send completed to the subscriber.
     * 
     * If any signal sends an error at any point, send that to the subscriber.
     */

    return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
        RACSignalBindBlock bindingBlock = block();

        __block volatile int32_t signalCount = 1;   // indicates self

        RACCompoundDisposable *compoundDisposable = [RACCompoundDisposable compoundDisposable];

        void (^completeSignal)(RACDisposable *) = ^(RACDisposable *finishedDisposable) {
            if (OSAtomicDecrement32Barrier(&signalCount) == 0) {
                [subscriber sendCompleted];
                [compoundDisposable dispose];
            } else {
                [compoundDisposable removeDisposable:finishedDisposable];
            }
        };

        void (^addSignal)(RACSignal *) = ^(RACSignal *signal) {
            OSAtomicIncrement32Barrier(&signalCount);

            RACSerialDisposable *selfDisposable = [[RACSerialDisposable alloc] init];
            [compoundDisposable addDisposable:selfDisposable];

            RACDisposable *disposable = [signal subscribeNext:^(id x) {
                [subscriber sendNext:x];
            } error:^(NSError *error) {
                [compoundDisposable dispose];
                [subscriber sendError:error];
            } completed:^{
                @autoreleasepool {
                    completeSignal(selfDisposable);
                }
            }];

            selfDisposable.disposable = disposable;
        };

        @autoreleasepool {
            RACSerialDisposable *selfDisposable = [[RACSerialDisposable alloc] init];
            [compoundDisposable addDisposable:selfDisposable];

            RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {
                // Manually check disposal to handle synchronous errors.
                if (compoundDisposable.disposed) return;

                BOOL stop = NO;
                id signal = bindingBlock(x, &stop);

                @autoreleasepool {
                    if (signal != nil) addSignal(signal);
                    if (signal == nil || stop) {
                        [selfDisposable dispose];
                        completeSignal(selfDisposable);
                    }
                }
            } error:^(NSError *error) {
                [compoundDisposable dispose];
                [subscriber sendError:error];
            } completed:^{
                @autoreleasepool {
                    completeSignal(selfDisposable);
                }
            }];

            selfDisposable.disposable = bindingDisposable;
        }

        return compoundDisposable;
    }] setNameWithFormat:@"[%@] -bind:", self.name];
}

其實(shí)就是創(chuàng)建了一個(gè)新的signal黔龟，然后在這個(gè)信號(hào)被訂閱的時(shí)候會(huì)執(zhí)行我們bind時(shí)候提供的block芍阎，根據(jù)我們?cè)赽ind里面返回的signal是不是空來(lái)決定是要addSignal還是addComplete至非。