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简介
函数响应式编程(Functional Reactive Programming:FRP)，ReactiveCocoa 版本 2.5
冷热信号
- 冷信号
只有当你订阅的时候，它才会发布消息，
一对一，当有不同的订阅者，消息是重新完整发送。
- 热信号
尽管你并没有订阅事件，但是它会时刻推送，类似“直播”，错过了就不再处理。
可以有多个订阅者，是一对多
RACSignal 与RACSubject 的区别
RACSignal是冷信号RACSubject是热信号
如下图
signal
image.png
subject
image.png
replaySubject
image.png
Subject可以附加行为，例如
RACReplaySubject具备为未来订阅者缓冲事件的能力。（这一点与冷信号类似，即使是在数据发送之后才订阅的，依然会收到全部消息）
冷信号示例：延时订阅，依然能收到所有信号数据
- (void)test1 {
RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[subscriber sendNext:@1];
[subscriber sendNext:@2];
[subscriber sendNext:@3];
[subscriber sendCompleted];
return nil;
}];
NSLog(@"Signal was created.");
[[RACScheduler mainThreadScheduler] afterDelay:0.1 schedule:^{
[signal subscribeNext:^(id x) {
NSLog(@"Subscriber1 recveive: %@", x);
}];
}];
[[RACScheduler mainThreadScheduler] afterDelay:1 schedule:^{
[signal subscribeNext:^(id x) {
NSLog(@"Subscriber2 recveive: %@", x);
}];
}];
}
image.png
热信号示例：错过了订阅时机，就收不到信号数据，类似于直播
冷信号会收到全部的数据，即使是在数据发送之后才订阅的
- (void)test2 {
RACMulticastConnection *connection = [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[[RACScheduler mainThreadScheduler] afterDelay:1 schedule:^{
[subscriber sendNext:@1];
}];
[[RACScheduler mainThreadScheduler] afterDelay:2 schedule:^{
[subscriber sendNext:@2];
}];
[[RACScheduler mainThreadScheduler] afterDelay:3 schedule:^{
[subscriber sendNext:@3];
[subscriber sendCompleted];
}];
return nil;
}] publish];
[connection connect];
NSLog(@"Signal was created.");
[[RACScheduler mainThreadScheduler] afterDelay:1.1 schedule:^{
[connection.signal subscribeNext:^(id x) {
NSLog(@"Subscriber1 recveive: %@", x);
}];
}];
[[RACScheduler mainThreadScheduler] afterDelay:2.1 schedule:^{
[connection.signal subscribeNext:^(id x) {
NSLog(@"Subscriber2 recveive: %@", x);
}];
}];
}
image.png
SideEffect示例：多次订阅导致信号block多次执行
- (void)test3 {
// 多次订阅会多次执行
RACSignal *requestSignal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSLog(@"开始请求网络数据");
[RACScheduler.mainThreadScheduler afterDelay:1 schedule:^{
[subscriber sendNext:@"1"];
}];
return nil;
}];
// 【请求数据次数 +1】
[requestSignal subscribeNext:^(id x) {
NSLog(@"订阅者1");
}];
// 【请求数据次数 +1】
[requestSignal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者2");
}];
// 将信号转换为内容为2的信号
RACSignal *signal1 = [requestSignal flattenMap:^RACStream *(id value) {
return [RACSignal return:@"2"];
}];
// 将signal1信号所有错误信息转换为字符串@"Error"
[signal1 catchTo:[RACSignal return:@"Error"]];
// 在没有获取值之前以字符串@"Loading..."占位
[signal1 startWith:@"Loading..."];
// 将信号进行绑定
// 【请求数据次数 +1】
RAC(self.acountField, text) = signal1;
// 订阅多个信号的任何错误，并且弹出UIAlertView
// 【请求数据次数 +2】
[[RACSignal merge:@[requestSignal, signal1]] subscribeError:^(NSError *error) {
NSLog(@"发生错误");
}];
}
image.png
解决方式一：使用 RACMulticastConnection把冷信号转化为热信号
- (void)test4 {
RACSignal *requestSignal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSLog(@"开始请求网络数据");
[RACScheduler.mainThreadScheduler afterDelay:1 schedule:^{
[subscriber sendNext:@"1"];
[subscriber sendCompleted];
}];
return nil;
}];
RACMulticastConnection *connection = [requestSignal multicast:[RACSubject subject]];
// RACMulticastConnection *connection = [requestSignal multicast:[RACReplaySubject subject]];
[connection connect];
[connection.signal subscribeNext:^(id x) {
NSLog(@"订阅者1:%@", x);
}];
[connection.signal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者2:%@", x);
}];
[RACScheduler.mainThreadScheduler afterDelay:2 schedule:^{
[connection.signal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者3:%@", x);
}];
}];
}
使用RACSubject时
RACMulticastConnection *connection = [requestSignal multicast:[RACSubject subject]];
image.png
使用RACReplaySubject时
RACMulticastConnection *connection = [requestSignal multicast:[RACReplaySubject subject]];
image.png
解决方式二：使用 replayLazily把冷信号转化为热信号
- (void)test5 {
RACSignal *requestSignal = [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSLog(@"开始请求网络数据");
[RACScheduler.mainThreadScheduler afterDelay:1 schedule:^{
[subscriber sendNext:@"1"];
[subscriber sendCompleted];
}];
return nil;
}] replayLazily]; // modify here!!
[requestSignal subscribeNext:^(id x) {
NSLog(@"订阅者1:%@", x);
}];
[requestSignal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者2:%@", x);
}];
[RACScheduler.mainThreadScheduler afterDelay:2 schedule:^{
[requestSignal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者3:%@", x);
}];
}];
}
image.png
使用RACCommand把冷信号转化为热信号
- (void)test6 {
RACCommand *requestCommand = [[RACCommand alloc] initWithSignalBlock:^RACSignal *(id input) {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
NSLog(@"开始请求网络数据");
[RACScheduler.mainThreadScheduler afterDelay:1 schedule:^{
[subscriber sendNext:@"1"];
[subscriber sendCompleted];
}];
return nil;
}];
}];
RACSignal *requestSignal = [requestCommand execute:nil];
[requestSignal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者1:%@", x);
}];
[requestSignal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者2:%@", x);
}];
[RACScheduler.mainThreadScheduler afterDelay:2 schedule:^{
[requestSignal subscribeNext:^(NSArray *x) {
NSLog(@"订阅者3:%@", x);
}];
}];
}
image.png
总结
RACMulticastConnection与RACSubject结合使用时是直播的热信号
RACCommand、replayLazily、RACReplaySubject都是类似于冷信号的情况，不管何时订阅，都会收到所有数据
ReactiveCocoa中潜在的内存泄漏与解决方案
RACObserve中潜在使用了self，要注意循环引用RACSubject中如果没有调用sendCompleted，调用map等操作将造成内存泄漏（循环引用）。RACSignal不会有这个问题
