concat、catchTo、never、takeUntil

1. - (RACSignal *)concat:(RACSignal *)signal

//源码
- (RACSignal *)concat:(RACSignal *)signal {
	return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
		RACSerialDisposable *serialDisposable = [[RACSerialDisposable alloc] init];

		RACDisposable *sourceDisposable = [self subscribeNext:^(id x) {
			[subscriber sendNext:x];
		} error:^(NSError *error) {
			[subscriber sendError:error];
		} completed:^{
			RACDisposable *concattedDisposable = [signal subscribe:subscriber];
			serialDisposable.disposable = concattedDisposable;
		}];

		serialDisposable.disposable = sourceDisposable;
		return serialDisposable;
	}] setNameWithFormat:@"[%@] -concat: %@", self.name, signal];
}

多个信号顺序输出，只有当前一个信号sendCompleted后一个信号才会执行。

//eg.
RACSignal *s1 = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
    [subscriber sendNext:@"1"];
    [subscriber sendCompleted];
    return nil;
}];

RACSignal *s2 = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
    [subscriber sendNext:@"2"];
    return nil;
}];

[[s1 concat:s2] subscribeNext:^(id x) {
    NSLog(@"%@",x);
}];

输出：

2020-07-06 17:39:06.542592+0800 C-41[3323:243230] 1
2020-07-06 17:39:06.542817+0800 C-41[3323:243230] 2

1. - (RACSignal *)catchTo:(RACSignal *)signal ``` //源码
2. (RACSignal *)catch:(RACSignal * (^)(NSError *error))catchBlock { NSCParameterAssert(catchBlock != NULL);

return [[RACSignal createSignal:^(id subscriber) { RACSerialDisposable *catchDisposable = [[RACSerialDisposable alloc] init];

RACDisposable *subscriptionDisposable = [self subscribeNext:^(id x) { [subscriber sendNext:x]; } error:^(NSError *error) { RACSignal *signal = catchBlock(error); NSCAssert(signal != nil, @“Expected non-nil signal from catch block on %@”, self); catchDisposable.disposable = [signal subscribe:subscriber]; } completed:^{ [subscriber sendCompleted]; }];

return [RACDisposable disposableWithBlock:^{ [catchDisposable dispose]; [subscriptionDisposable dispose]; }]; }] setNameWithFormat:@”[%@] -catch:“, self.name]; }

当某个信号发生错误时`senderError`，将替补信号的值作为备选值。

//eg. RACSignal *s1 = [RACSignal createSignal:^RACDisposable *(id subscriber) { [subscriber sendError:nil]; return nil; }];

RACSignal *s2 = [RACSignal createSignal:^RACDisposable *(id subscriber) { [subscriber sendNext:@“替补队员跟上”]; return nil; }];

[[s1 catchTo:s2] subscribeNext:^(id x) { NSLog(@“%@”,x); }];

输出：

2020-07-06 17:48:06.347187+0800 C-41[3418:248921] 替补队员跟上


3. `+ (RACSignal *)never`

//源码 + (RACSignal *)never { return [[self createSignal:^ RACDisposable * (id subscriber) { return nil; }] setNameWithFormat:@“+never”]; }

订阅者永远收不到订阅值；没有错误；没有完成。



4. `- (RACSignal *)takeUntil:(RACSignal *)signalTrigger`

//源码 - (RACSignal *)takeUntil:(RACSignal *)signalTrigger { return [[RACSignal createSignal:^(id subscriber) { RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable]; void (^triggerCompletion)(void) = ^{ [disposable dispose]; [subscriber sendCompleted]; };

RACDisposable *triggerDisposable = [signalTrigger subscribeNext:^(id _) { triggerCompletion(); } completed:^{ triggerCompletion(); }];

[disposable addDisposable:triggerDisposable];

RACDisposable *selfDisposable = [self subscribeNext:^(id x) { [subscriber sendNext:x]; } error:^(NSError *error) { [subscriber sendError:error]; } completed:^{ [disposable dispose]; [subscriber sendCompleted]; }];

[disposable addDisposable:selfDisposable];

return disposable; }] setNameWithFormat:@”[%@] -takeUntil: %@“, self.name, signalTrigger]; }

正在进行的信号叫做A信号，遇到信号B被订阅就停止。
首先，通过A信号创建了一个中间信号A1。开始时对A信号进行了了订阅，并将值作为A1信号的输出。当B信号被订阅时，会触发A1信号的`sendCompleted`操作。这样无理A怎么发消息，A1都不会转发。

//eg. RACSubject *untilSignal = [RACSubject subject]; RACSubject *afterUntilSignal = [RACSubject subject];

[[afterUntilSignal takeUntil:untilSignal] subscribeNext:^(id x) { NSLog(@“%@”,x); }];

[untilSignal subscribeNext:^(id x) { NSLog(@“%@”,x); }];

[afterUntilSignal sendNext:@“1”]; [afterUntilSignal sendNext:@“2”]; [untilSignal sendNext:@“stop”]; [afterUntilSignal sendNext:@“3”]; ``` 输出

2020-07-06 17:42:51.878488+0800 C-41[3354:245702] 1
2020-07-06 17:42:51.878642+0800 C-41[3354:245702] 2
2020-07-06 17:42:51.878854+0800 C-41[3354:245702] stop