前言
最近，ReactiveCocoa火的不行，网上各种大牛各种说RAC的优点，早就有学习的想法，一直没有付诸行动，最近公司开发不是很紧张，特意学习了一下RAC，以便以后改版使用。
1.[-subscribe…][RACSignal]该方法会检测RACSignal中当前和以后的值，来执行subscribe中相应的方法。
example:
RACSignal *letters = [@“a b c d e f” componentsSeparatedByString:@“ “].rac_sequence.signal;
//数组中的元素分割成多个信号
[letters subscribeNext:^(id x){
NSLog(@“%@“, x);
}];
//letters信号的subscriber在signal的值改变时执行相应方法
output:a b c d e f(每一行输出一个字母)
2.[-subscribe…][RACSignal]
__block unsigned subscriptions =0;RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id subscriber) { subscriptions++; [subscriber sendCompleted];returnnil;}];
// Outputs:// subscription 1[loggingSignal subscribeCompleted:^{NSLog(@"subscription %u", subscriptions);}];// Outputs:// subscription 2[loggingSignal subscribeCompleted:^{NSLog(@"subscription %u", subscriptions);}];
执行顺序：创建RACSignal ->执行subscribeCompleted->回调createSignal中的方法-执行[subscriber sendCompleted]->回调[loggingSignal subscribeCompleted:]中的方法
总结：[RACSignal subscribeCompleted:] [RACSignal subscribeNext:]都会回调createSignl中的block中的方法，但是block中的[sendCompleted] [sendNext]只会执行他回调的方法，即谁回调执行谁。 但是，[doNext]和[doCompleted]中的block会执行。
3.[-do…][RACSignal+Operations] ([doNext:][RACSignal] [doCompleted:][RACSignal])
__blockunsignedsubscriptions =0;RACSignal *loggingSignal = [RACSignal createSignal:^ RACDisposable * (id subscriber) { subscriptions++; [subscriber sendCompleted];returnnil;}];// Does not output anything yetloggingSignal = [loggingSignal doCompleted:^{NSLog(@"about to complete subscription %u", subscriptions);}];// Outputs:// about to complete subscription 1// subscription 1[loggingSignal subscribeCompleted:^{NSLog(@"subscription %u", subscriptions);}];
执行doCompleted或者doNext时，必须返回RACSignal,否则，不会执行其block。[doNext:][doCompleted]不会像[subscribeCompleted:][subscribeNext:]那样主动去回调[createSignal:][RACSignal]中的block,而是，当[subscribe doNext:][subscribe doComplete]时执行相应的动作。
4.[-map:][RACStream]
map:映射的意思，此方法可以将一个信号映射成一个新的任意类型的信号。
RACSequence *letters = [@"A B C D E F G H I"componentsSeparatedByString:@" "].rac_sequence;// Contains: AA BB CC DD EE FF GG HH IIRACSequence *mapped = [letters map:^(NSString *value) {return[valuestringByAppendingString:value];}];
RACSequence *mapped2 = [letters map:(^NSString *value){
return @([value isEqualToString:@“a”]);
}];
如上，可以将原来的letters信号串map成@“AA BB CC DD EE FF GG HH II”信号串，也可以map成BOOL类型的信号串
5.[-filter:][RACStream]
筛选符合条件的信号，组成一个只包含符合条件信号的信号流。
RACSequence *numbers = [@"1 2 3 4 5 6 7 8 9"componentsSeparatedByString:@" "].rac_sequence;// Contains: 2 4 6 8RACSequence *filtered = [numbers filter:^ BOOL (NSString *value) {return(value.intValue %2) ==0;}];
如图，过滤出符合条件的signal；
6.[-concat:][RACStream]
将一个信号流添加到另一个信号流后面。
RACSequence*letters= [@"A B C D E F G H I" componentsSeparatedByString:@""].rac_sequence;RACSequence*numbers= [@"123456789" componentsSeparatedByString:@""].rac_sequence;//Contains: A B C D E F G H I123456789RACSequence*concatenated= [letters concat:numbers];
7.[-flatten][RACStream]
(1)将两个sequence合成一个sequence，其实质就是concatenated。
RACSequence*letters= [@"A B C D E F G H I" componentsSeparatedByString:@""].rac_sequence;RACSequence*numbers= [@"123456789" componentsSeparatedByString:@""].rac_sequence;RACSequence*sequenceOfSequences=@[letters, numbers ].rac_sequence;//Contains: A B C D E F G H I123456789RACSequence*flattened= [sequenceOfSequences flatten];
（2）将两个signal合成一个signal，其实质就是merge。
RACSubject*letters= [RACSubject subject];RACSubject*numbers= [RACSubject subject];RACSignal*signalOfSignals= [RACSignal createSignal:^ RACDisposable * (id subscriber) { [subscriber sendNext:letters];[subscriber sendNext:numbers];[subscriber sendCompleted];returnnil;}];RACSignal*flattened= [signalOfSignals flatten];//Outputs: A1B C2[flattened subscribeNext:^(NSString*x) { NSLog(@"%@",x);}];[letters sendNext:@"A"];[numbers sendNext:@"1"];[letters sendNext:@"B"];[letters sendNext:@"C"];[numbers sendNext:@"2"];
调用顺序：createSignal->[flattend subscribeNext:]->[createSignal (^block)]->[letters sendNext:]->[flattend subscribeNext:^block]…(之后重复，sendNext之后，回调subscribeNext)；
8.[-flattenMap:][RACStream]
实质：mapping和flattening
RACSequence*numbers= [@"123456789" componentsSeparatedByString:@""].rac_sequence;//Contains:112233445566778899RACSequence*extended= [numbers flattenMap:^(NSString*num) {return@[num, num ].rac_sequence;}];//Contains:1_3_5_7_9_RACSequence*edited= [numbers flattenMap:^(NSString*num) {if(num.intValue %2==0) {return[RACSequence empty]; }else{ NSString*newNum= [num stringByAppendingString:@"_"];
return [RACSequence return:newNum];
}
}];
9.[-then:][RACSignal+Operations]
RACSignal *letters = [@"A B C D E F G H I"componentsSeparatedByString:@" "].rac_sequence.signal;// The new signal only contains:123456789//// But when subscribed to, it also outputs: A B C D E F G H IRACSignal *sequenced =[[letters doNext:^(NSString *letter) { NSLog(@"%@", letter); }] then:^{return[@"1 2 3 4 5 6 7 8 9"componentsSeparatedByString:@" "].rac_sequence.signal; }];
sequenced.signal subscribeNext:^(id x){
NSLog(@“%@“, x); //输出1 2 3 4 5 6 7 8，并不会输出A B C D E F G H I
}
执行完doNext:中的方法后，返回一个新的signal给原来的信号，并去执行subscribeNext中的相应方法
10.[+merge:][RACSignal+Operations]
将两个信号流合成一个信号流
RACSubject*letters= [RACSubject subject];RACSubject*numbers= [RACSubject subject];RACSignal*merged= [RACSignal merge:@[letters, numbers ]];//Outputs: A1B C2[merged subscribeNext:^(NSString*x) { NSLog(@"%@", x);}];[letters sendNext:@"A"];[numbers sendNext:@"1"];[letters sendNext:@"B"];[letters sendNext:@"C"];[numbers sendNext:@"2"];
[-subscribeNext:]相当于水管出水口，当[-sendNext:]有水注入时，水管出口就会有相应的水流出。
11.[+combineLatest:][RACSignal+Operations] and [+combineLatest:reduce:]
观察所有信号的状况，当有信号发生改变时，会将最后改变的信号发送给监听者。
RACSubject*letters= [RACSubject subject];RACSubject*numbers= [RACSubject subject];RACSignal*combined= [RACSignal combineLatest:@[letters, numbers ] reduce:^(NSString*letter, NSString*number) {return[letter stringByAppendingString:number]; }];//Outputs: B1 B2 C2 C3[combined subscribeNext:^(idx) { NSLog(@"%@", x);}];[letters sendNext:@"A"];[letters sendNext:@"B"];[numbers sendNext:@"1"];[numbers sendNext:@"2"];[letters sendNext:@"C"];[numbers sendNext:@"3"];
12.[-switchToLatest][RACSignal+Operations]
用于信号和信号之间，总是选择最新的信号给另一个。
RACSubject*letters= [RACSubject subject];RACSubject*numbers= [RACSubject subject];RACSubject*signalOfSignals= [RACSubject subject];RACSignal*switched= [signalOfSignals switchToLatest];//Outputs: A B1D [switched subscribeNext:^(NSString*x) { NSLog(@"%@",x);}];[signalOfSignals sendNext:letters];[letters sendNext:@"A"];[letters sendNext:@"B"];[signalOfSignals sendNext:numbers];[letters sendNext:@"C"];[numbers sendNext:@"1"];[signalOfSignals sendNext:letters];[numbers sendNext:@"2"];[letters sendNext:@"D"];