• RACSubject :信號(hào)提供者,自己可以充當(dāng)信號(hào),又能夠發(fā)送信號(hào)

@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

基本使用

#import "ViewController.h"
#import <ReactiveObjC/ReactiveObjC.h>

@interface ViewController ()

@end

@implementation ViewController


- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    
    // 1.訂閱信號(hào)
    RACSubject *subject = [RACSubject subject];
    
    // 2.訂閱信號(hào)
    // 不同的信號(hào)砚尽，訂閱方式不一樣（因?yàn)轭愋筒灰粯樱哉{(diào)用方法不一樣）
    [subject subscribeNext:^(id  _Nullable x) {
       
        NSLog(@"第1個(gè)訂閱信號(hào)中的內(nèi)容是: %@", x);
    }];
    
    [subject subscribeNext:^(id  _Nullable x) {
        
        NSLog(@"第2個(gè)訂閱信號(hào)中的內(nèi)容是: %@", x);
    }];
    
    [subject subscribeNext:^(id  _Nullable x) {
        
        NSLog(@"第3個(gè)訂閱信號(hào)中的內(nèi)容是: %@", x);
    }];
    
    // 3.發(fā)送信號(hào)
    // 遍歷出所有的訂閱者,調(diào)用nextBlock
    [subject sendNext:@"subject的信號(hào)"];
}

過(guò)程分析

RACSubject.png

• 創(chuàng)建信號(hào)

// RACSubject
// 創(chuàng)建一個(gè)容量為1的數(shù)組
+ (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;
}

• 訂閱信號(hào)

// RACSignal
// 訂閱信號(hào) 調(diào)用父類的方法 RACSignal 
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
    NSCParameterAssert(nextBlock != NULL);
    
    // 創(chuàng)建訂閱者    在內(nèi)部 保存了 nextBlock
    RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
    
    return [self subscribe:o]; // 注意此時(shí)的 self 是 RACSubject
}

// RACSubject
// 保存訂閱者

// This should only be used while synchronized on `self`.
@property (nonatomic, strong, readonly) NSMutableArray *subscribers;


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

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

    NSMutableArray *subscribers = self.subscribers;
    @synchronized (subscribers) {
        
        // 保存訂閱者
        [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;
}

• 發(fā)送信號(hào)

// RACSubject 

// This should only be used while synchronized on `self`.
@property (nonatomic, strong, readonly) NSMutableArray *subscribers;

// 遍歷每個(gè)一個(gè)訂閱都 進(jìn)行逐一發(fā)送消息
- (void)enumerateSubscribersUsingBlock:(void (^)(id<RACSubscriber> subscriber))block {
    NSArray *subscribers;
    @synchronized (self.subscribers) {
        subscribers = [self.subscribers copy];
    }

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

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

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

        nextBlock(value);
    }
}