初始化 BehaviorSubject<T> 类的新实例，该类创建一个缓存其最后一个值并从指定值开始的主题。
Namespace：System.Reactive.Subjects
装配： System.Reactive.dll) 中的 System.Reactive (
语法
'Declaration
Public Sub New ( _
value As T _
)
'Usage
Dim value As T
Dim instance As New BehaviorSubject(value)
public BehaviorSubject(
T value
)
public:
BehaviorSubject(
T value
)
new :
value:'T -> BehaviorSubject
public function BehaviorSubject(
value : T
)
parameters
- value
类型： T
当使用者尚未收到其他值时，发送给观察者的初始值。
备注
BehaviorSubject 缓冲它通过其 IObservable 接口发布的最后一项。 如果尚未通过其 IObservable 接口发布任何项，则构造函数中提供的初始项是当前缓冲的项。 订阅 BehaviorSubject 的 IObservable 接口时，发布的序列从当前缓冲的项开始。
一旦 BehaviorSubject 的 IObserver 接口收到完成，则不会缓冲或发布任何项。
示例
此示例演示 BehaviorSubject。 该示例使用 Interval 运算符每秒向整数序列发布一个整数。 发布 10 个整数后，Take 运算符将完成序列。 这是 BehaviorSubject 订阅的序列。
为 BehaviorSubject 的 IObservable 接口创建两个订阅，以显示它如何发布数据。
订阅 #1 ：此订阅将从头开始，并显示序列中构造函数 (-9) 的初始缓冲值。
订阅 #2 ：此订阅将在睡眠 5 秒后启动。 此订阅显示序列以当前缓冲的项开头。
using System;
using System.Reactive.Linq;
using System.Reactive.Subjects;
using System.Reactive.Concurrency;
using System.Threading;
namespace Example
{
class Program
{
static void Main()
{
//********************************************************************************************************//
//*** A subject acts similar to a proxy in that it acts as both a subscriber and a publisher ***//
//*** It's IObserver interface can be used to subscribe to multiple streams or sequences of data. ***//
//*** The data is then published through it's IObservable interface. ***//
//*** ***//
//*** A BehaviorSubject buffers the last item it published through its IObservable interface. If no ***//
//*** item has been published through its IObservable interface then the initial item provided in the ***//
//*** constructor is the current buffered item. When a subscription is made to the BehaviorSubject's ***//
//*** IObservable interface, the sequence published begins with the currently buffered item. ***//
//*** ***//
//*** No items are buffered or published from a BehaviorSubject once its IObserver interface receives ***//
//*** a completion. ***//
//*** ***//
//*** In this example, we use the Interval operator to publish an integer to a integer sequence every ***//
//*** second. The sequence will be completed by the Take operator after 10 integers are published. ***//
//*** This will be the sequence that the BehaviorSubject subscribes to. ***//
//*** ***//
//*** We will create 2 subscriptions to the BehaviorSubject's IObservable interface to show how it ***//
//*** publishes it's data. ***//
//*** ***//
//*** Subscription #1 : This subscription will start at the very beginning and will show the initial ***//
//*** buffered value from the constructor (-9) in the sequence. ***//
//*** ***//
//*** Subscription #2 : This subscription will start after a 5 sec. sleep showing the sequence starts ***//
//*** with the currently buffered item. ***//
//********************************************************************************************************//
BehaviorSubject<long> myBehaviorSubject = new BehaviorSubject<long>((-9));
Observable.Interval(TimeSpan.FromSeconds(1), Scheduler.ThreadPool).Take(10).Subscribe(myBehaviorSubject);
//********************************************************************************************************//
//*** Subscription #1 : This subscription will start at the very beginning and will show the initial ***//
//*** buffered value from the constructor (-9) in the sequence. ***//
//********************************************************************************************************//
EventWaitHandle wait1 = new EventWaitHandle(false, EventResetMode.ManualReset);
myBehaviorSubject.Subscribe(x => Console.WriteLine("Subscription #1 observes : " + x),
() =>
{
Console.WriteLine("Subscription #1 completed.");
wait1.Set();
});
//********************************************************************************************************//
//*** Subscription #2 : This subscription will start after a 5 sec. sleep showing the sequence starts ***//
//*** with the currently buffered item. ***//
//********************************************************************************************************//
Thread.Sleep(5000);
EventWaitHandle wait2 = new EventWaitHandle(false, EventResetMode.ManualReset);
myBehaviorSubject.Subscribe(x => Console.WriteLine("{0,30}Subscription #2 observes : {1}", " ", x),
() =>
{
Console.WriteLine("{0,30}Subscription #2 completed.", " ");
wait2.Set();
});
//**************************************************//
// *** Wait for completion on both subscriptions ***//
//**************************************************//
WaitHandle.WaitAll(new WaitHandle[] { wait1, wait2 });
myBehaviorSubject.Dispose();
Console.WriteLine("\nPress ENTER to exit...");
Console.ReadLine();
}
}
}
示例代码的以下输出显示了重叠的订阅。
Subscription #1 observes : -9
Subscription #1 observes : 0
Subscription #1 observes : 1
Subscription #1 observes : 2
Subscription #1 observes : 3
Subscription #1 observes : 4
Subscription #2 observes : 4
Subscription #1 observes : 5
Subscription #2 observes : 5
Subscription #1 observes : 6
Subscription #2 observes : 6
Subscription #1 observes : 7
Subscription #2 observes : 7
Subscription #1 observes : 8
Subscription #2 observes : 8
Subscription #1 observes : 9
Subscription #2 observes : 9
Subscription #1 completed.
Subscription #2 completed.
Press ENTER to exit...