Question

这是关于RAC 2.0的问题，我很陌生：

我们说我有一个信号：

<receiver android:name=".AlarmReceiver" android:process=":remote" />

当我的应用程序启动时，我想要

- (RACSignal *)signalWithAsyncWorkInIt;

但是sig2的RACSignal *sig1 = [self.signalWithAsyncWorkInIt subscribeNext:...]; // then somewhere else later: RACSignal *sig2 = [self.signalWithAsyncWorkInIt subscribeNext:...]; // looking for some option other than subscribeNext:方法不会触发signalWithAsyncWorkInIt的执行，如果sig1已经或者只是要这样做，那么sig2只会重放＆＃34;最新结果＆＃34; of signalWithAsyncWorkInIt如果它存在并等待sig1等其他东西触发signalWithAsyncWorkInIt它是第一次它还没有被触发。

Answer 1

我不确定我是否理解正确，但也许您正在寻找的是replay，replayLast或replayLazily。

通过重放，您可以避免多次执行信号。它将结果多播到多个订阅者，而不执行每个订阅的操作。

简单示例：

RACSignal* asyncOperationSignal = [[RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
    NSLog(@"execute something here and return with the result");
    [subscriber sendNext:@"42"];
    return nil;
}]
replayLazily]; // call replayLazily to make sure the operation only executes after the first subscription
               // and returns the result for every consecutive subscription

[asyncOperationSignal subscribeNext:^(NSString* result) {
    NSLog(@"Result: %@", result);
}];

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 3 * NSEC_PER_SEC), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // subscribe again later in the code
    [asyncOperationSignal subscribeNext:^(NSString* result) {
        NSLog(@"Result: %@", result);
    }];
});

输出将是：

execute something here and return with the result
42
42

这是一篇关于这个主题的写得很好的文章： http://spin.atomicobject.com/2014/06/29/replay-replaylast-replaylazily/

RAC：如何懒惰地订阅信号，即如果该信号已经或将要由其他用户执行，则不会触发其执行？

1 个答案: