📜  RxPY-使用主题

📅  最后修改于: 2020-11-06 06:40:07             🧑  作者: Mango


主题既是可观察的序列,也是可以多播的观察者,即与已订阅的许多观察者交谈。

我们将讨论以下主题主题-

  • 创建一个主题
  • 订阅主题
  • 将数据传递给主题
  • 行为主体
  • 重播主题
  • 异步主题

创建一个主题

要处理主题,我们需要导入主题,如下所示:

from rx.subject import Subject

您可以按如下方式创建主题对象-

subject_test = Subject()

该对象是具有三种方法的观察者-

  • on_next(值)
  • on_error(错误)和
  • on_completed()

订阅主题

您可以在主题上创建多个订阅,如下所示:

subject_test.subscribe(
   lambda x: print("The value is {0}".format(x))
)
subject_test.subscribe(
   lambda x: print("The value is {0}".format(x))
)

将数据传递给主题

您可以将数据传递给使用on_next(value)方法创建的主题,如下所示-

subject_test.on_next("A")
subject_test.on_next("B")

数据将传递给所有订阅,并添加到主题上。

这是该主题的一个实际例子。

from rx.subject import Subject
subject_test = Subject()
subject_test.subscribe(
   lambda x: print("The value is {0}".format(x))
)
subject_test.subscribe(
   lambda x: print("The value is {0}".format(x))
)
subject_test.on_next("A")
subject_test.on_next("B")

subject_test对象是通过调用Subject()创建的。 subject_test对象引用了on_next(value),on_error(error)和on_completed()方法。上面示例的输出如下所示-

输出

E:\pyrx>python testrx.py
The value is A
The value is A
The value is B
The value is B

我们可以使用on_completed()方法来停止主题执行,如下所示。

from rx.subject import Subject
subject_test = Subject()
subject_test.subscribe(
   lambda x: print("The value is {0}".format(x))
)
subject_test.subscribe(
   lambda x: print("The value is {0}".format(x))
)
subject_test.on_next("A")
subject_test.on_completed()
subject_test.on_next("B")

一旦调用完成,就不会调用后面调用的下一个方法。

输出

E:\pyrx>python testrx.py
The value is A
The value is A

现在让我们看看如何调用on_error(error)方法。

from rx.subject import Subject
subject_test = Subject()
subject_test.subscribe(
   on_error = lambda e: print("Error : {0}".format(e))
)
subject_test.subscribe(
   on_error = lambda e: print("Error : {0}".format(e))
)
subject_test.on_error(Exception('There is an Error!'))

输出

E:\pyrx>python testrx.py
Error: There is an Error!
Error: There is an Error!

行为主体

当被调用时,BehaviorSubject将为您提供最新的值。您可以如下所示创建行为主题-

from rx.subject import BehaviorSubject
behavior_subject = BehaviorSubject("Testing Behaviour Subject"); // initialized the behaviour subject with value:Testing Behaviour Subject

这是使用行为主题的有效示例

from rx.subject import BehaviorSubject
behavior_subject = BehaviorSubject("Testing Behaviour Subject");
behavior_subject.subscribe(
   lambda x: print("Observer A : {0}".format(x))
)
behavior_subject.on_next("Hello")
behavior_subject.subscribe(
   lambda x: print("Observer B : {0}".format(x))
)
behavior_subject.on_next("Last call to Behaviour Subject")

输出

E:\pyrx>python testrx.py
Observer A : Testing Behaviour Subject
Observer A : Hello
Observer B : Hello
Observer A : Last call to Behaviour Subject
Observer B : Last call to Behaviour Subject

重播主题

重播主题类似于行为主题,其中,它可以缓冲值并将其重播给新订户。这是重放主题的一个有效示例。

from rx.subject import ReplaySubject
replay_subject = ReplaySubject(2)
replay_subject.subscribe(lambda x: print("Testing Replay Subject A: {0}".format(x)))
replay_subject.on_next(1)
replay_subject.on_next(2)
replay_subject.on_next(3)
replay_subject.subscribe(lambda x: print("Testing Replay Subject B: {0}".format(x)));
replay_subject.on_next(5)

重播主题上使用的缓冲区值为2。因此,最后两个值将被缓冲并用于新的订户。

输出

E:\pyrx>python testrx.py
Testing Replay Subject A: 1
Testing Replay Subject A: 2
Testing Replay Subject A: 3
Testing Replay Subject B: 2
Testing Replay Subject B: 3
Testing Replay Subject A: 5
Testing Replay Subject B: 5

异步主题

对于AsyncSubject,最后一次调用的值将传递给订阅服务器,并且只有在调用complete()方法之后才能完成。

from rx.subject import AsyncSubject
async_subject = AsyncSubject()
async_subject.subscribe(lambda x: print("Testing Async Subject A: {0}".format(x)))
async_subject.on_next(1)
async_subject.on_next(2)
async_subject.on_completed()
async_subject.subscribe(lambda x: print("Testing Async Subject B: {0}".format(x)))
Here, before complete is called, the last value passed to the subject is 2, and the same is given to the subscribers.

输出

E:\pyrx>python testrx.py
Testing Async Subject A: 2
Testing Async Subject B: 2