RXScala中的热和冷可观测量有什么区别？

冷可观察性是可观察的,在订阅时开始产生价值.

被动的流并根据请求开始发布.

一些例子：

import rx.lang.scala._
import org.joda.time._

val onetwothree = Observable.just(1,2,3) // when subscribed each subscriber will get 1,and 3
// scala> onetwothree.subscribe(println(_))
// 1
// 2
// 3
// res1: rx.lang.scala.Subscription = rx.lang.scala.Subscription$$anon$2@11be372a

// When subscribed will get one event with current DateTime
val currentTime = Observable.defer {
  Observable.just(DateTime.now)
}
// scala> currentTime.subscribe(println(_))
// 2015-01-19T14:13:37.333+02:00

// scala> currentTime.subscribe(println(_))
// 2015-01-19T14:13:38.742+02:00

// scala> currentTime.subscribe(println(_))
// 2015-01-19T14:13:40.448+02:00

// And this one is tricky.
val loggedInUsers = Obserable.defer {
  fetchLoggedUsersFromDb
}

热门观察

无论订阅如何,都处于活动状态并发布的流.

自然的例子来自UI编程：鼠标点击流.无论是否订阅了流,都会产生点击.

在许多应用程序中,loggedInUsers被称为温暖可观察的东西：

val loggedInUsers = updateTriggers.concatMap { _ => 
  fetchLoggedUsersFromDb
}.replay(1)

当上次触发updateTriggers时,此流的subriber将立即获得一个值,即已记录的用户.还有连续的更新.

温暖的观察

val hot = mouseClicks

// Observable that will replay all of its items and notifications to any future Observer
// i.e. all mouseClicks from the time point we called `.replay`
val cold = hot.replay

但是之间有一些东西：

// Observable that will replay at most 10 items emitted by `hot`
val warm = hot.replay(10)

当我们订阅热门时,它会立即发出最后10次点击,并在此之后继续发出点击.