RAC

RACSubject

//創(chuàng)建信號(hào)
RACSubject *subject = [RACSubject subject];
//訂閱信號(hào)
[subject subscribeNext:^(id  _Nullable x) {
      NSLog(@"subscribeNext %@",x);
}];
//發(fā)送信號(hào) 
[subject sendNext:@"1"];

分析

step1: 先看下RACSubject

@interface RACSubject<ValueType> : RACSignal<ValueType> <RACSubscriber>

/// Returns a new subject.
+ (instancetype)subject;

// Redeclaration of the RACSubscriber method. Made in order to specify a generic type.
- (void)sendNext:(nullable ValueType)value;

@end

發(fā)現(xiàn)RACSubject繼承于RACSignal，有一個(gè)初始化方法subject和一個(gè)發(fā)送信號(hào)的方法 sendNext

step2: 查看subject方法

+ (instancetype)subject {
    return [[self alloc] init];
}

- (instancetype)init {
    self = [super init];
    if (self == nil) return nil;

    _disposable = [RACCompoundDisposable compoundDisposable];
    _subscribers = [[NSMutableArray alloc] initWithCapacity:1];
    
    return self;
}

調(diào)用了[[self alloc] init]方法，并對(duì)init方法進(jìn)行重寫(xiě)，在init中對(duì)兩個(gè)屬性進(jìn)行了初始化

  • 看下屬性的聲明
// Contains all current subscribers to the receiver.
//
// This should only be used while synchronized on `self`.
@property (nonatomic, strong, readonly) NSMutableArray *subscribers;

// Contains all of the receiver's subscriptions to other signals.
@property (nonatomic, strong, readonly) RACCompoundDisposable *disposable;

用一個(gè)數(shù)組保存所有的訂閱者，另一個(gè)對(duì)象用來(lái)取消訂閱

step3: 查看訂閱subscribeNext:方法，這是父類(lèi)的方法

- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
    NSCParameterAssert(nextBlock != NULL);
    
    RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
    return [self subscribe:o];
}
  • 創(chuàng)建訂閱者
+ (instancetype)subscriberWithNext:(void (^)(id x))next error:(void (^)(NSError *error))error completed:(void (^)(void))completed {
    RACSubscriber *subscriber = [[self alloc] init];

    subscriber->_next = [next copy];
    subscriber->_error = [error copy];
    subscriber->_completed = [completed copy];

    return subscriber;
}

創(chuàng)建一個(gè)訂閱者，將傳進(jìn)來(lái)的參數(shù)賦值給訂閱者的成員變量，在例子中就是將訂閱的block與訂閱者關(guān)聯(lián)上。

  • subscribe 調(diào)用的是RACSubject類(lèi)中的subscribe 
- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
    NSCParameterAssert(subscriber != nil);
        //創(chuàng)建一個(gè)取消訂閱對(duì)象
    RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable];
       //訂閱者
    subscriber = [[RACPassthroughSubscriber alloc] initWithSubscriber:subscriber signal:self disposable:disposable];
        //最關(guān)鍵的代碼
        //將上一步創(chuàng)建好的訂閱者對(duì)象保存在第一步創(chuàng)建的數(shù)組中
    NSMutableArray *subscribers = self.subscribers;
    @synchronized (subscribers) {
        [subscribers addObject:subscriber];
    }
    
    [disposable addDisposable:[RACDisposable disposableWithBlock:^{
        @synchronized (subscribers) {
            // Since newer subscribers are generally shorter-lived, search
            // starting from the end of the list.
            NSUInteger index = [subscribers indexOfObjectWithOptions:NSEnumerationReverse passingTest:^ BOOL (id<RACSubscriber> obj, NSUInteger index, BOOL *stop) {
                return obj == subscriber;
            }];

            if (index != NSNotFound) [subscribers removeObjectAtIndex:index];
        }
    }]];

    return disposable;
}

將上一步創(chuàng)建的訂閱者保存在第一步創(chuàng)建的數(shù)組中

step4: 查看sendNext：方法

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

遍歷所有的訂閱者

  • 查看遍歷方法
- (void)enumerateSubscribersUsingBlock:(void (^)(id<RACSubscriber> subscriber))block {
    NSArray *subscribers;
    @synchronized (self.subscribers) {
        subscribers = [self.subscribers copy];
    }

    for (id<RACSubscriber> subscriber in subscribers) {
        block(subscriber);
    }
}

self.subscribers是第一步中創(chuàng)建的數(shù)組，遍歷數(shù)組將其中的訂閱者對(duì)象取出來(lái)，調(diào)用傳進(jìn)來(lái)的block方法。

  • 查看遍歷回調(diào)中的sendNext，這是調(diào)用的RACSubscriber的方法
- (void)sendNext:(id)value {
    @synchronized (self) {
        void (^nextBlock)(id) = [self.next copy];
        if (nextBlock == nil) return;

        nextBlock(value);
    }
}

從訂閱者對(duì)象中取出next變量，即第二步中訂閱信號(hào)時(shí)的block，然后調(diào)用這個(gè)block方法。

RACSignal

既然從前面得知RACSubject繼承于RACSignal，那我們就研究下RACSignal

// 1.創(chuàng)建信號(hào)
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        // 3.發(fā)送信號(hào)
        [subscriber sendNext:@"liu"];
        //發(fā)送完成信號(hào) 并取消訂閱
        [subscriber sendCompleted];
        // 4.取消信號(hào)，如果信號(hào)想要被取消，就必須返回一個(gè)RACDisposable
        return [RACDisposable disposableWithBlock:^{
            NSLog(@"取消訂閱");
        }];
    }];
    
    [signal subscribeNext:^(id x) {
        // block的調(diào)用時(shí)刻：只要信號(hào)內(nèi)部發(fā)出數(shù)據(jù)就會(huì)調(diào)用這個(gè)block
        NSLog(@"======%@", x);
    }];

運(yùn)行結(jié)果

源碼分析

step1: 查看createSignal方法

+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
    return [RACDynamicSignal createSignal:didSubscribe];
}

//簡(jiǎn)單看下 RACDynamicSignal
//一個(gè)私有的RACSignal子類(lèi)實(shí)現(xiàn)它們的訂閱行為
// A private `RACSignal` subclasses that implements its subscription behavior
// using a block.
@interface RACDynamicSignal : RACSignal

+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe;

@end
  • 查看RACDynamicSignal類(lèi)中的createSignal方法
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
    RACDynamicSignal *signal = [[self alloc] init];
    signal->_didSubscribe = [didSubscribe copy];
    return [signal setNameWithFormat:@"+createSignal:"];
}

這個(gè)方法中主要做了兩件事

  • 1、創(chuàng)建一個(gè)信號(hào)量對(duì)象
  • 2、將外面?zhèn)鬟M(jìn)來(lái)的block保存在信號(hào)量對(duì)象的_didSubscribe變量中

step2: 查看訂閱信號(hào)subscribeNext

- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
    NSCParameterAssert(nextBlock != NULL);
    
    RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
    return [self subscribe:o];
}

這個(gè)方法主要做了兩件事

  • 1、創(chuàng)建訂閱者

  • 2、執(zhí)行訂閱命令

  • subscriberWithNext: error: completed:前面已經(jīng)講過(guò)，這里就不再講述

  • 查看subscribe:方法，是在RACDynamicSignal類(lèi)中

- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
    NSCParameterAssert(subscriber != nil);

    RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable];
    subscriber = [[RACPassthroughSubscriber alloc] initWithSubscriber:subscriber signal:self disposable:disposable];

    if (self.didSubscribe != NULL) {
        RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
            RACDisposable *innerDisposable = self.didSubscribe(subscriber);
            [disposable addDisposable:innerDisposable];
        }];

        [disposable addDisposable:schedulingDisposable];
    }
    
    return disposable;
}

關(guān)鍵代碼在self.didSubscribe(subscriber);，在創(chuàng)建信號(hào)量時(shí)將傳進(jìn)來(lái)的block 賦值給了self.didSubscribe，此時(shí)調(diào)用self.didSubscribe(subscriber);即調(diào)用block并將訂閱者對(duì)象傳進(jìn)去

問(wèn)題是self.didSubscribe(subscriber);的調(diào)用這是在block中，那這個(gè)block是在什么時(shí)候調(diào)用？

  • 查看schedule方法，是RACSubscriptionScheduler類(lèi)的方法
- (RACDisposable *)schedule:(void (^)(void))block {
    NSCParameterAssert(block != NULL);

    if (RACScheduler.currentScheduler == nil) return [self.backgroundScheduler schedule:block];

    block();
    return nil;
}

可以看到傳進(jìn)來(lái)的參數(shù)block被調(diào)用

step3: sendNext發(fā)送信號(hào)

- (void)sendNext:(id)value {
    @synchronized (self) {
        void (^nextBlock)(id) = [self.next copy];
        if (nextBlock == nil) return;

        nextBlock(value);
    }
}

從訂閱者對(duì)象中取出next變量，即第二步中訂閱信號(hào)時(shí)的block，然后調(diào)用這個(gè)block方法

RACReplaySubject

RACReplaySubject *subject = [RACReplaySubject subject];
[subject subscribeNext:^(id  _Nullable x) {
     NSLog(@"subscribeNext - %@",x);
}];
[subject sendNext:@"liu"];

運(yùn)行結(jié)果

subscribeNext - liu

源碼分析

step1: 先看下它的.h文件

保存它發(fā)送的值
/// A replay subject saves the values it is sent (up to its defined capacity)
/// and resends those to new subscribers. It will also replay an error or
/// completion.
@interface RACReplaySubject<ValueType> : RACSubject<ValueType>

/// Creates a new replay subject with the given capacity. A capacity of
/// RACReplaySubjectUnlimitedCapacity means values are never trimmed.
+ (instancetype)replaySubjectWithCapacity:(NSUInteger)capacity;

@end

RACReplaySubject是RACSubject的子類(lèi)，對(duì)外只暴露了一個(gè)replaySubjectWithCapacity方法，這是個(gè)初始化方法

step2: 看下replaySubjectWithCapacity方法實(shí)現(xiàn)

+ (instancetype)replaySubjectWithCapacity:(NSUInteger)capacity {
    return [(RACReplaySubject *)[self alloc] initWithCapacity:capacity];
}

- (instancetype)init {
    return [self initWithCapacity:RACReplaySubjectUnlimitedCapacity];
}

- (instancetype)initWithCapacity:(NSUInteger)capacity {
    self = [super init];
    
    _capacity = capacity;
    _valuesReceived = (capacity == RACReplaySubjectUnlimitedCapacity ? [NSMutableArray array] : [NSMutableArray arrayWithCapacity:capacity]);
    
    return self;
}

不管是通過(guò)自己的初始化方法replaySubjectWithCapacity，還是通過(guò)父類(lèi)的初始化方法subject，最終都會(huì)調(diào)用initWithCapacity方法，在initWithCapacity方法里創(chuàng)建了一個(gè)數(shù)組用來(lái)存儲(chǔ)發(fā)送信號(hào)時(shí)傳遞的數(shù)據(jù)。

step2: 訂閱信號(hào)subscribeNext

- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
    NSCParameterAssert(nextBlock != NULL);
    
    RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
    return [self subscribe:o];
}

  • 第一步創(chuàng)建訂閱者與父類(lèi)是相同的，創(chuàng)建一個(gè)訂閱者并將block保存在訂閱者的成員變量中。

  • 第二步調(diào)用的RACReplaySubject自己的方法

- (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)];
            }

            if (compoundDisposable.disposed) return;

            if (self.hasCompleted) {
                [subscriber sendCompleted];
            } else if (self.hasError) {
                [subscriber sendError:self.error];
            } else {
                RACDisposable *subscriptionDisposable = [super subscribe:subscriber];
                [compoundDisposable addDisposable:subscriptionDisposable];
            }
        }
    }];

    [compoundDisposable addDisposable:schedulingDisposable];

    return compoundDisposable;
}

會(huì)遍歷第一步創(chuàng)建的數(shù)組保存的數(shù)據(jù)，然后發(fā)送信號(hào)，即訂閱信號(hào)流程中包含發(fā)送信號(hào)。

step3: 發(fā)送信號(hào)sendNext，注意這是在RACReplaySubject中實(shí)現(xiàn)

- (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];
    }
}

會(huì)將發(fā)送的數(shù)據(jù)保存在第一步創(chuàng)建的數(shù)組中以便訂閱信號(hào)時(shí)使用，最終發(fā)送信號(hào)還是調(diào)用的父類(lèi)的方法。

問(wèn)題： RACReplaySubject 與 RACSubject有什么區(qū)別

RACSubject中代碼必須按照 創(chuàng)建信號(hào)--> 訂閱信號(hào) --> 發(fā)送信號(hào)，這樣的先后順序，否則無(wú)效；而在RACReplaySubject中創(chuàng)建信號(hào)后，訂閱信號(hào)與發(fā)送信號(hào)順序無(wú)所謂。

所以RACReplaySubject寫(xiě)成下面這樣也是可以的。

RACReplaySubject *subject = [RACReplaySubject subject];
[subject sendNext:@"liu"];
[subject subscribeNext:^(id  _Nullable x) {
      NSLog(@"subscribeNext - %@",x);
}];

RACCommand

- (void)testRACCommand {
    
    /**
     *  RACCommand使用注意
     *  1、RACCommand內(nèi)部必須返回RACSignal
     *  2、executionSignals信號(hào)中的信號(hào)，一開(kāi)始獲取不到內(nèi)部信號(hào)
     *      2.1 使用switchToLatest:獲取內(nèi)部信號(hào)
     *      2.2 使用execute:獲取內(nèi)部信號(hào)
     *  3、executing判斷是否正在執(zhí)行
     *      3.1 第一次不準(zhǔn)確，需要skip:跳過(guò)
     *      3.2 一定要記得sendCompleted，否則永遠(yuǎn)不會(huì)執(zhí)行完成
     *  4、通過(guò)執(zhí)行execute，執(zhí)行command的block
     */
    
    RACCommand *command = [[RACCommand alloc] initWithSignalBlock:^RACSignal * _Nonnull(id  _Nullable input) {
        return [RACSignal createSignal:^RACDisposable * _Nullable(id<RACSubscriber>  _Nonnull subscriber) {
            [subscriber sendNext:@"發(fā)送第1條信號(hào)"];
            [subscriber sendCompleted];
            return nil;
        }];
    }];
    
    [command.executionSignals.switchToLatest subscribeNext:^(id  _Nullable x) {

    }];
    
    [[command.executing skip:1] subscribeNext:^(NSNumber * _Nullable x) {
        //NSLog(@"x = %@", x);
        if (x.boolValue) {
            NSLog(@"x = %@ 正在執(zhí)行", x);
        } else {
            NSLog(@"x = %@ 執(zhí)行完成", x);
        }
    }];
    
    [command execute:@1];
    
}

源碼分析

step1: 查看RACCommand類(lèi)的.h文件

1. executionSignals:需要執(zhí)行的block成功的時(shí)候返回的信號(hào)，他是在主線程執(zhí)行的。
2. executing：信號(hào)量  監(jiān)聽(tīng)RACCommand的狀態(tài)
3. enabled:當(dāng)前命令是否enabled，默認(rèn)是no，他也可以根據(jù)enableSignal來(lái)設(shè)置或者allowsConcurrentExecution設(shè)置為NO的時(shí)候（command已經(jīng)開(kāi)始執(zhí)行）
4. errors:執(zhí)行command的時(shí)候獲取的error都會(huì)通過(guò)這個(gè)信號(hào)發(fā)送
5. allowsConcurrentExecution：是否允許并發(fā)執(zhí)行command，默認(rèn)是NO。

6.initWithSignalBlock:(RACSignal * (^)(id input))signalBlock:初始化RACCommand，參數(shù)為返回一個(gè)信號(hào)的block，即block返回的是executionSignals
7.- (id)initWithEnabled:(RACSignal *)enabledSignal signalBlock:(RACSignal * (^)(id input))signalBlock:第一個(gè)參數(shù)設(shè)置當(dāng)前command是否可用，第二個(gè)是執(zhí)行的block。enableed默認(rèn)是yes，所以第二個(gè)參數(shù)也可以為nil。
8.execute:(id)input：調(diào)用command，input為executionSignals的訂閱者發(fā)送的值

step2: 查看初始化方法

- (instancetype)initWithSignalBlock:(RACSignal<id> * (^)(id input))signalBlock {
    return [self initWithEnabled:nil signalBlock:signalBlock];
}

- (instancetype)initWithEnabled:(RACSignal *)enabledSignal signalBlock:(RACSignal<id> * (^)(id input))signalBlock {
    NSCParameterAssert(signalBlock != nil);

    self = [super init];

    _addedExecutionSignalsSubject = [RACSubject new];
    _allowsConcurrentExecutionSubject = [RACSubject new];
    _signalBlock = [signalBlock copy];

    _executionSignals = [[[self.addedExecutionSignalsSubject
        map:^(RACSignal *signal) {
            return [signal catchTo:[RACSignal empty]];
        }]
        deliverOn:RACScheduler.mainThreadScheduler]
        setNameWithFormat:@"%@ -executionSignals", self];
    
    // `errors` needs to be multicasted so that it picks up all
    // `activeExecutionSignals` that are added.
    //
    // In other words, if someone subscribes to `errors` _after_ an execution
    // has started, it should still receive any error from that execution.
    RACMulticastConnection *errorsConnection = [[[self.addedExecutionSignalsSubject
        flattenMap:^(RACSignal *signal) {
            return [[signal
                ignoreValues]
                catch:^(NSError *error) {
                    return [RACSignal return:error];
                }];
        }]
        deliverOn:RACScheduler.mainThreadScheduler]
        publish];
    
    _errors = [errorsConnection.signal setNameWithFormat:@"%@ -errors", self];
    [errorsConnection connect];

    RACSignal *immediateExecuting = [[[[self.addedExecutionSignalsSubject
        flattenMap:^(RACSignal *signal) {
            return [[[signal
                catchTo:[RACSignal empty]]
                then:^{
                    return [RACSignal return:@-1];
                }]
                startWith:@1];
        }]
        scanWithStart:@0 reduce:^(NSNumber *running, NSNumber *next) {
            return @(running.integerValue + next.integerValue);
        }]
        map:^(NSNumber *count) {
            return @(count.integerValue > 0);
        }]
        startWith:@NO];

    _executing = [[[[[immediateExecuting
        deliverOn:RACScheduler.mainThreadScheduler]
        // This is useful before the first value arrives on the main thread.
        startWith:@NO]
        distinctUntilChanged]
        replayLast]
        setNameWithFormat:@"%@ -executing", self];
    
    RACSignal *moreExecutionsAllowed = [RACSignal
        if:[self.allowsConcurrentExecutionSubject startWith:@NO]
        then:[RACSignal return:@YES]
        else:[immediateExecuting not]];
    
    if (enabledSignal == nil) {
        enabledSignal = [RACSignal return:@YES];
    } else {
        enabledSignal = [enabledSignal startWith:@YES];
    }
    
    _immediateEnabled = [[[[RACSignal
        combineLatest:@[ enabledSignal, moreExecutionsAllowed ]]
        and]
        takeUntil:self.rac_willDeallocSignal]
        replayLast];
    
    _enabled = [[[[[self.immediateEnabled
        take:1]
        concat:[[self.immediateEnabled skip:1] deliverOn:RACScheduler.mainThreadScheduler]]
        distinctUntilChanged]
        replayLast]
        setNameWithFormat:@"%@ -enabled", self];

    return self;
}

將傳進(jìn)來(lái)的block拷貝到變量_signalBlock 中，以便后面使用。

step3: 查看command.executing subscribeNext:，訂閱信號(hào)從而獲取RACCommand的狀態(tài)

- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
    NSCParameterAssert(nextBlock != NULL);
    
    RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
    return [self subscribe:o];
}

點(diǎn)擊subscribeNext進(jìn)入的是RACSignal文件，但是查看self會(huì)發(fā)現(xiàn)是RACReplaySubject

  • 進(jìn)入RACReplaySubject的subscribe方法
- (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)];
            }

            if (compoundDisposable.disposed) return;

            if (self.hasCompleted) {
                [subscriber sendCompleted];
            } else if (self.hasError) {
                [subscriber sendError:self.error];
            } else {
                RACDisposable *subscriptionDisposable = [super subscribe:subscriber];
                [compoundDisposable addDisposable:subscriptionDisposable];
            }
        }
    }];

    [compoundDisposable addDisposable:schedulingDisposable];

    return compoundDisposable;
}

step4: RACCommand執(zhí)行命令execute

- (RACSignal *)execute:(id)input {
    // `immediateEnabled` is guaranteed to send a value upon subscription, so
    // -first is acceptable here.
    BOOL enabled = [[self.immediateEnabled first] boolValue];
    if (!enabled) {
        NSError *error = [NSError errorWithDomain:RACCommandErrorDomain code:RACCommandErrorNotEnabled userInfo:@{
            NSLocalizedDescriptionKey: NSLocalizedString(@"The command is disabled and cannot be executed", nil),
            RACUnderlyingCommandErrorKey: self
        }];

        return [RACSignal error:error];
    }

    RACSignal *signal = self.signalBlock(input);
    NSCAssert(signal != nil, @"nil signal returned from signal block for value: %@", input);

    // We subscribe to the signal on the main thread so that it occurs _after_
    // -addActiveExecutionSignal: completes below.
    //
    // This means that `executing` and `enabled` will send updated values before
    // the signal actually starts performing work.
    RACMulticastConnection *connection = [[signal
        subscribeOn:RACScheduler.mainThreadScheduler]
        multicast:[RACReplaySubject subject]];
    
    [self.addedExecutionSignalsSubject sendNext:connection.signal];

    [connection connect];
    return [connection.signal setNameWithFormat:@"%@ -execute: %@", self, RACDescription(input)];
}
  • self.signalBlock(input)，self.signalBlock是第一步中外部傳進(jìn)來(lái)的block，這句代碼就是執(zhí)行外面的block

RACTuple

在 CocoaReactive 中，有些信號(hào)流傳遞的信號(hào)量是由其他多個(gè)信號(hào)流傳遞的信號(hào)量組合而成的，而這多個(gè)信號(hào)量則是封裝在一個(gè) RACTuple 實(shí)例中進(jìn)行傳遞的。

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