ReactiveCocoa信号高阶操作

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一升阶和降阶

二

1.创造高阶信号

(1)RACSignal*signal = [RACSignalreturn:@1];

RACSignal*signalHighOrder = [RACSignalreturn:signal];

(2)RACSignal *anotherSignal = [signalmap:^id(idvalue) {

return [RACSignalreturn:value];

}];

2.订阅高阶信号

RACSignal*signal =@[@1,@2,@3].rac_sequence.signal;

RACSignal*highOrderSignal = [signalmap:^id(idvalue) {

return [RACSignalreturn:value];

}];

[highOrderSignalsubscribeNext:^(RACSignal*aSignal) {

[aSignalsubscribeNext:^(idx) {

// get real value here.

}]; }];

三降阶操作

1.SwitchToLatests

信号1 信号2(将信号1关闭) 信号4 信号5与高阶信号信号6 信号7 判断信号是否结束

示例一

RACSignal*autoRunButtonClickSignal = [self.autoRunBtn rac_signalForControlEvents:UIControlEventTouchUpInside];

RACSignal*oneStepButtonClickSignal = [self.oneStepBtn

rac_signalForControlEvents:UIControlEventTouchUpInside];

RACSignal*idSignal = [RACSignalreturn:nil];

RACSignal*timerSignal = [RACSignalinterval:1 onScheduler:[RACScheduler mainThreadScheduler]];

autoRunButtonClickSignal = [autoRunButtonClickSignalmapReplace:idSignal];

oneStepButtonClickSignal = [oneStepButtonClickSignalmapReplace:timerSignal];

RACSignal*controlSignal = [autoRunButtonClickSignalmerge: oneStepButtonClickSignal];

controlSignal = [controlSignal switchToLatest];

示例二搜索请求

网络差连续发送不同的请求有时后搜索的会先返回造成搜索不准

RACSignal*searchTextSignal = [self.searchTextField rac_textSignal];

RACSignal*requestSignals = [searchTextSignalmap:^id(NSString*searchText) {

NSString *urlString = [NSStringstringWithFormat:

@"http://xxxx.xxx.xxx/?q=%@", searchText];

NSURL *url = [NSURLURLWithString:urlString];

NSURLRequest *request = [NSURLRequestrequestWithURL:url];

return [NSURLConnectionrac_sendAsynchronousRequest:request];

}];

//第二个信号去请求时会把第一个信号关掉

requestSignals = [requestSignals switchToLatest];

2.If/then/else

If/then/else本质&类似操作

+ (RACSignal*)if:(RACSignal*)boolSignal

then:(RACSignal*)trueSignal

else:(RACSignal*)falseSignal {

return [[boolSignal

map:^(NSNumber*value) {

return (value.boolValue? trueSignal : falseSignal);

}]

switchToLatest];

}

+ (RACSignal*)switch:(RACSignal*)signal

cases:(NSDictionary*)cases

default:(RACSignal*)defaultSignal;

3.Flatten 不会丢数据扁平

异步并发同时允许2段并发(此时已经满了,黄色和绿色信号) 绿色信号或黄色信号结束了橙色信号才会开始

Flatten:1的思考

-返回 a 信号,b 信号的高阶信号 flatten:1 相当于 a信号concat:b信号

- (RACSignal *)concat;

concat 与1秒延迟信号

RACSignal *signal = @[@1, @3, @7,@9, @8].rac_sequence.signal;

RACSignal *timerSignal = [[signal map:^id(id value) {

return [[RACSignal return:value] delay:1];

}] concat];

降阶操作总结

SwitchToLatests (将上一个信号抛弃)

Flatten (Merge)

Concat (Flatten:1)

四思考

1.改变某个值的个数

返回的是1,2,2,3,3,3

RACSignal *signal = @[@1, @2, @3].rac_sequence.signal;

RACSignal *mappedSignal = [[signal map:^id(NSNumber *value) {

return [[[RACSignal return:value] repeat] take:value.integerValue];

}] flatten];

2.将一个值改为一个错误

RACSignal *signal = @[@1,@2,@3,@0].rac_sequence.signal;

RACSignal *mappedSignal = [[signal map:^id(NSNumber *value) { if(value.integerValue ==0) {

return [RACSignal error:[NSError errorWithDomain:@"0"code:0 }else {

return[RACSignalreturn:value];

}

}] flatten];

3.改变值的时间间隔

RACSignal *signal = @[@"♪5",@"♬1",@"♬2",@"♬3",@"♩4"]

.rac_sequence

.signal;

NSDictionary*toneLengthMap =@{@"♩":@0.5,

@"♪":@0.25,

@"♬":@0.125};

RACSignal*mappedSignal = [[signalmap:^id(NSString*value) {

NSString *tone = [value substringFromIndex:1];

NSString *length = [value substringToIndex:1];

NSNumber *toneValue = @(tone.integerValue);

NSNumber *toneLength = toneLengthMap[length];

return [[RACSignalreturn:toneValue]

concat:[[RACSignalempty]

delay: toneLength.doubleValue]];

}] concat];

delay 是不靠谱的(concat一个 empty 信号,delay 延长)

4.Map————>Flatten FlattenMap 高阶—>降阶

五 FlattenMap

1.重要性

可以用 FlattenMap 实现很多的信号转换

支持串行异步操作(类似 Promise)

满足 Monad 部分定义 (bind 和 return 才完全满足)

FlattenMap要求传入信号,然后返回扁平化后的 value

RACSignal*flatten = [signal flattenMap:^RACStream *(RACSignal *value) {

return value;

}];

RACSignal*map = [signal flattenMap:^RACStream *(idvalue) {

id anotherValue = value;// map here!

return [RACSignal return: anotherValue];

}];

过滤掉空的值

RACSignal*filter = [signal flattenMap:^RACStream *(idvalue) {

BOOL filter = (value ==nil);// filter here!

return filter ? [RACSignal empty] : [RACSignal return:value];

}];

在实际使用时的重要场景

RACSignal*signal = [RACSignalreturn:@"http://xx.com/a"];

RACSignal*getSignal = [signalflattenMap: ^RACStream*(NSString*url) {

NSURLRequest *request = [NSURLRequestrequestWithURL:[NSURLURLWithString:url]];

return [NSURLConnectionrac_sendAsynchronousRequest:request];

}];

RACSignal*jsonSignal = [getSignalflattenMap: ^RACStream*(NSData*data) {

NSError *error = nil;

id result = [NSJSONSerializationJSONObjectWithData:dataoptions:0error:&error];

return error == nil ? [RACSignalreturn:result]: [RACSignalerror: error];

}];

RACSignal*getItemSignal = [jsonSignalflattenMap: ^RACStream*(NSDictionary*value) {

if (![valueisKindOfClass:[NSDictionaryclass]] || value[@"data.url"] == nil) {

return [RACSignal error:someError];

}

NSURLRequest *anotherRequest = [NSURLRequestrequestWithURL:[NSURLURLWithString:value[@"data.url"]]];

return [NSURLConnectionrac_sendAsynchronousRequest:anotherRequest];

}];

2.FlattenMap 与 monad,bind

Functor,Applicative,Monad 概念
FlattenMap 符合 Monad 的 bind 定义,但是无法实现 takeUntil:操作,无法做副作用操作例如 take:的计数

- (instancetype)flattenMap:(RACStream * (^)(idvalue))block;

- (instancetype)bind:(RACStreamBindBlock (^)(void))block;

typedef RACStream * (^RACStreamBindBlock)(idvalue,BOOL *stop);

3.bind妙用

- (RACSignal*)take:(NSUInteger)count {

if (count ==0)return [RACSignalempty];

return [selfbind:^{

__block NSUInteger taken = 0;

return ^ id (idvalue,BOOL *stop) {

if (taken < count) {

++taken;

if (taken == count) *stop =YES;

return [class return:value];

}else {

return nil; }

}; }];

}

4.bind简单实现和问题

- (RACSignal*)bind:(RACStreamBindBlock(^)(void))block;

{

return [RACSignalcreateSignal:^RACDisposable*(id<RACSubscriber> subscriber) {

RACStreamBindBlock bindBlock = block();

[selfsubscribeNext:^(idx) {

BOOL stop =NO;

RACSignal *signal = (RACSignal *)bindBlock(x, &stop);

if (signal ==nil || stop) { [subscriber sendCompleted];

}else {

[signal subscribeNext:^(idx) { [subscriber sendNext:x];

} error:^(NSError *error) { [subscriber sendError:error];

} completed:^{ }];

}

} error:^(NSError *error) { [subscriber sendError:error];

} completed:^{ [subscriber sendCompleted]; }];

return nil;

}]; }

六有用的高阶操作

- (RACSignal *)try:(BOOL(^)(idvalue, NSError **errorPtr))tryBlock; 对每个值进行分析,用来简化 flattenMap 等操作

- (RACSignal*)tryMap:(id(^)(idvalue, NSError **errorPtr))mapBlock;

- (RACSignal *)catch:(RACSignal * (^)(NSError *error))catchBlock;

- (RACSignal*)catchTo:(RACSignal*)signal;

- (RACSignal *)timeout:(NSTimeInterval)interval

onScheduler:(RACScheduler *)scheduler;

七扩展问题

不能信号是 pushDriver 只能被动接收浓缩信号变短(冷热信号操作)

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