RAC源碼分析
簡要而言：RAC事實(shí)上就是對block進(jìn)行copy和封裝开镣，在需要的時(shí)候進(jìn)行調(diào)用的時(shí)候再拿出來調(diào)用。在signal的創(chuàng)建階段保存創(chuàng)建block荚藻，在subscribe階段調(diào)用創(chuàng)建的block來創(chuàng)建一個(gè)subscriber并在subscriber中保存需要執(zhí)行的block屋灌，最后在send階段執(zhí)行執(zhí)行的block。綜上应狱，RACSignal就是保存一個(gè)構(gòu)造函數(shù)共郭，再執(zhí)行構(gòu)造函數(shù)生成observer保存執(zhí)行函數(shù)，在sendnext執(zhí)行保存的執(zhí)行函數(shù)，一共兩步保存兩步執(zhí)行：保存除嘹、執(zhí)行+保存写半、執(zhí)行 分別對應(yīng)create，subscribe和send階段尉咕。
RACSignal
self.signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[blockButton addTarget:subscriber action:@selector(sendNext:) forControlEvents:UIControlEventTouchUpInside];
return [RACDisposable disposableWithBlock:^{
[blockButton removeTarget:subscriber action:@selector(sendNext:) forControlEvents:UIControlEventTouchUpInside];
}];
}];
- 以上這個(gè)代碼塊還尚未被調(diào)用只是被保存了下來留到subscribe的時(shí)候使用它創(chuàng)建一個(gè)subscriber叠蝇，進(jìn)入createSignal的實(shí)現(xiàn)看到：
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
return [RACDynamicSignal createSignal:didSubscribe];
}
- 創(chuàng)建的是一個(gè)DynamicSignal，看這名字好像是Signal的一個(gè)子類年缎？點(diǎn)開一看針地秀悔捶！為什么父類的create方法怎么調(diào)用子類的創(chuàng)建方法，RACSignal在.m文件中偷偷包含了子類DynamicSignal的.h文件晦款。RACSignal把傳入的參數(shù)原封不動(dòng)地傳給了子類的構(gòu)建函數(shù)炎功，意思就是：你要?jiǎng)?chuàng)建一個(gè)可以工作的信號(hào)？好的我自己比較抽象缓溅，只負(fù)責(zé)指導(dǎo)兒子們工作，我派我最得意的兒子動(dòng)態(tài)信號(hào)給你干活赁温。點(diǎn)開子類DynamicSignal的創(chuàng)建方法：
+ (RACSignal *)createSignal:(RACDisposable * (^)(id<RACSubscriber> subscriber))didSubscribe {
RACDynamicSignal *signal = [[self alloc] init];
signal->_didSubscribe = [didSubscribe copy];
return [signal setNameWithFormat:@"+createSignal:"];
}
- 真正干活的兒子復(fù)制了自己的一個(gè)本地坛怪，然后保存了一個(gè)didSubscribe的備份，質(zhì)疑道signal是copy類型的代碼塊指針股囊，被copy和strong指針指向的代碼塊都會(huì)在堆區(qū)復(fù)制一個(gè)副本來袜匿，這里就完成了第一步的保存，保存的是subscribe代碼塊稚疹，也就是構(gòu)建subscriber的代碼塊居灯。
[self.signal subscribeNext:^(id x) {
NSLog(@"仙人板板");
}];
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
NSCParameterAssert(nextBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
return [self subscribe:o];
}
- 哦？創(chuàng)建了一個(gè)RACSubscriber内狗，初始化的時(shí)候把這個(gè)next當(dāng)參數(shù)傳進(jìn)去了怪嫌，還傳了兩個(gè)NULL值。什么時(shí)候這個(gè)NULL值不是NULL呢柳沙？
- (RACDisposable *)subscribeError:(void (^)(NSError *error))errorBlock {
NSCParameterAssert(errorBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:NULL error:errorBlock completed:NULL];
return [self subscribe:o];
}
- (RACDisposable *)subscribeCompleted:(void (^)(void))completedBlock {
NSCParameterAssert(completedBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:NULL error:NULL completed:completedBlock];
return [self subscribe:o];
}
- 往下看岩灭，哦，subscribeNext就把block當(dāng)next傳進(jìn)去了赂鲤，subscribeError噪径，就把block當(dāng)error傳進(jìn)去了，傳subscribeCompleted就把block當(dāng)completed參數(shù)傳進(jìn)去了数初；對罢野！都傳也行泡孩！
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock error:(void (^)(NSError *error))errorBlock completed:(void (^)(void))completedBlock {
NSCParameterAssert(nextBlock != NULL);
NSCParameterAssert(errorBlock != NULL);
NSCParameterAssert(completedBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:errorBlock completed:completedBlock];
return [self subscribe:o];
}
- subscribeNext车摄，subscribecompleted，subscribeError，分三個(gè)函數(shù)執(zhí)行和一起執(zhí)行的區(qū)別就是創(chuàng)建了三個(gè)subscriber分別保存一個(gè)block和一個(gè)subscriber保存三個(gè)block的區(qū)別练般。哦矗漾，結(jié)尾還執(zhí)行了[self subscribe:0];點(diǎn)開:誒，怎么還需要選擇類薄料？注意到執(zhí)行的是[self subscribe:o];剛才創(chuàng)建的是dynamicSignal敞贡，所以選的是DynamicSignal；如果你點(diǎn)開的是RACSignal摄职，會(huì)出現(xiàn)這樣一句代碼：
NSCAssert(NO, @"This method must be overridden by subclasses");
- 父類的subscribe函數(shù)必須要子類重寫誊役，所以剛才選擇的那些項(xiàng)都是Signal的子類，發(fā)現(xiàn)其中還有RACSubject谷市，打開DynamicSignal的subscribe函數(shù):
- (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;
}
- 重點(diǎn)在這里：RACDisposable *innerDisposable = self.didSubscribe(subscriber);執(zhí)行了一次didSubscribe代碼塊蛔垢，這個(gè)didSubscribe代碼塊是怎么拿到的？見上文dynamicSignal的create函數(shù)第二句：signal->_didSubscribe = [didSubscribe copy];就是在創(chuàng)建的時(shí)候復(fù)制了一份block到堆中迫悠，（因?yàn)樵诤瘮?shù)中聲明的block通常為棧block鹏漆，函數(shù)結(jié)束就隨生命周期結(jié)束釋放了，而通常create创泄，subscribe和send都是在不同的函數(shù)中調(diào)用的艺玲，block必須保存為堆block）。所以在這個(gè)didSubscribe代碼塊中需要做就是規(guī)定好observer的觸發(fā)條件鞠抑，網(wǎng)上一大堆例子直接在didSubscribe塊中調(diào)用了[observer sendNext]和[observer sendCompleted]組合;這個(gè)是什么觸發(fā)條件饭聚？只在調(diào)用didSubscribe執(zhí)行的時(shí)候才會(huì)發(fā)射信號(hào)。搁拙。秒梳。原諒我沒有看懂這種操作，這種信號(hào)之后是怎么觸發(fā)的呢箕速？
- 以上是第二步的“執(zhí)行+保存”酪碘。執(zhí)行的是didsubscribe，保存的是next弧满，completed婆跑，error三種block。
- 最后一步send就簡單了庭呜，假裝在didSubcribe代碼塊中寫一句[subcriber sendNext:nil];(因?yàn)閟ignal對外沒有sendNext方法暴露出來滑进，只能調(diào)用subcriber的sendNext方法，不過沒關(guān)系募谎，只是點(diǎn)進(jìn)去看看)代碼如下:
- (void)sendNext:(id)value {
@synchronized (self) {
void (^nextBlock)(id) = [self.next copy];
if (nextBlock == nil) return;
nextBlock(value);
}
}
- 懂了扶关，直接運(yùn)行了之前保存好的nextBlock；那我sendCompleted呢数冬？直接completedBlock()节槐？那還用薛呀搀庶？當(dāng)巖了！error呢铜异？哥倔。。揍庄。
- (void)sendCompleted {
@synchronized (self) {
void (^completedBlock)(void) = [self.completed copy];
[self.disposable dispose];
if (completedBlock == nil) return;
completedBlock();
}
}
- 給出RACSignal使用的正確姿勢:textField_signal咆蒿；引入ReactiveCocoa頭文件，隨便創(chuàng)建一個(gè)textfield;textField.rac_textSignal,點(diǎn)進(jìn)去rac_textSignal,代碼如下：
- (RACSignal *)rac_textSignal {
@weakify(self);
return [[[[[RACSignal
defer:^{
@strongify(self);
return [RACSignal return:self];
}]
concat:[self rac_signalForControlEvents:UIControlEventAllEditingEvents]]
map:^(UITextField *x) {
return x.text;
}]
takeUntil:self.rac_willDeallocSignal]
setNameWithFormat:@"%@ -rac_textSignal", self.rac_description];
}
- 類別為textField添加textSignal屬性蚂子。重點(diǎn)在這:[self rac_signalForControlEvents:UIControlEventAllEditingEvents]]點(diǎn)進(jìn)去看到：
- (RACSignal *)rac_signalForControlEvents:(UIControlEvents)controlEvents {
@weakify(self);
return [[RACSignal
createSignal:^(id<RACSubscriber> subscriber) {
@strongify(self);
[self addTarget:subscriber action:@selector(sendNext:) forControlEvents:controlEvents];
[self.rac_deallocDisposable addDisposable:[RACDisposable disposableWithBlock:^{
[subscriber sendCompleted];
}]];
return [RACDisposable disposableWithBlock:^{
@strongify(self);
[self removeTarget:subscriber action:@selector(sendNext:) forControlEvents:controlEvents];
}];
}]
setNameWithFormat:@"%@ -rac_signalForControlEvents: %lx", self.rac_description, (unsigned long)controlEvents];
}
- 重點(diǎn)在這:[self addTarget:subscriber action:@selector(sendNext:) forControlEvents:controlEvents];哦沃测，在這里每次textField發(fā)生event都會(huì)到subscriber中調(diào)用nextBlock。使用一個(gè)信號(hào)就實(shí)現(xiàn)了對events的監(jiān)聽食茎。若仿照其實(shí)現(xiàn)對一個(gè)按鈕的點(diǎn)擊事件的監(jiān)聽：
self.signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[blockButton addTarget:subscriber action:@selector(sendNext:) forControlEvents:UIControlEventTouchUpInside];
return [RACDisposable disposableWithBlock:^{
[blockButton removeTarget:subscriber action:@selector(sendNext:) forControlEvents:UIControlEventTouchUpInside];
}];
}];
- 在didSubscribe塊中直接[subScriber sendNext];的寫法有什么使用場景蒂破。。我一直沒搞明白别渔；上面這個(gè)寫法值得注意的是如果在disposableblock中沒有removeTarget是沒法正常綁定的附迷，這個(gè)問題我問了很多討論群里的大神，都沒有給出比較好的答案钠糊，暫時(shí)存疑挟秤。disposible塊中通常做一些類似dealloc函數(shù)里面進(jìn)行的操作。
- Subject繼承自RACSignal抄伍，可以直接[subject sendNext];棕叫，這個(gè)sendNext是把存在subject數(shù)組中的所有subscriber遍歷一遍都執(zhí)行nextBlock:
- (void)sendNext:(id)value {
[self enumerateSubscribersUsingBlock:^(id<RACSubscriber> subscriber) {
[subscriber sendNext:value];
}];
}
結(jié)束
