BehaviorSubject < T > 建構函式
初始化BehaviorSubject < T >類別的新實例，這個類別會建立主旨來快取其最後一個值，並以指定的值開頭。
Namespace：System.Reactive.Subjects
裝配： System.Reactive.dll) 中的 System.Reactive (
語法
'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
)
參數
- value
類型： T
當主體尚未收到其他值時，傳送給觀察者的初始值。
備註
BehaviorSubject 會緩衝它透過其 IObservable 介面發佈的最後一個專案。 如果尚未透過其 IObservable 介面發佈任何專案，則建構函式中提供的初始專案是目前緩衝的專案。 當對 BehaviorSubject 的 IObservable 介面進行訂閱時，發行的順序會以目前緩衝的專案開始。
一旦 IObserver 介面收到完成，就不會從 BehaviorSubject 緩衝或發佈任何專案。
範例
此範例示範 BehaviorSubject。 此範例會使用 Interval 運算子每秒將整數發佈至整數序列。 發行 10 個整數之後，Take 運算子將會完成序列。 這是 BehaviorSubject 訂閱的順序。
會為 BehaviorSubject 的 IObservable 介面建立兩個訂用帳戶，以顯示其發佈資料的方式。
訂用帳戶#1：此訂用帳戶會從開頭開始，並顯示序列中建構函式的初始緩衝值 (-9) 。
訂用帳戶#2：此訂用帳戶會在 5 秒睡眠後啟動。 此訂用帳戶會顯示序列開頭為目前緩衝的專案。
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();
}
}
}
範例程式碼的下列輸出會顯示重迭的訂用帳戶。
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...