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WorkflowQueue Class

Represents a workflow queue.


Namespace:  System.Workflow.Runtime
Assembly:  System.Workflow.Runtime (in System.Workflow.Runtime.dll)

Public Class WorkflowQueue

The WorkflowQueue type exposes the following members.

Public propertyCountGets the number of items contained in the WorkflowQueue.
Public propertyEnabledGets or sets a value that specifies whether the WorkflowQueue is enabled.
Public propertyQueueNameGets the name of the workflow queue.
Public propertyQueuingServiceGets the queuing service associated with this WorkflowQueue.

Public methodDequeueRemoves and returns the object at the beginning of the WorkflowQueue.
Public methodEnqueueAdds an object to the end of the WorkflowQueue.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodPeekReturns the object at the beginning of the WorkflowQueue without removing it.
Public methodRegisterForQueueItemArrivedRegisters a subscriber to the QueueItemArrived event.
Public methodRegisterForQueueItemAvailable(IActivityEventListener(Of QueueEventArgs))Registers a subscriber to the QueueItemAvailable event.
Public methodRegisterForQueueItemAvailable(IActivityEventListener(Of QueueEventArgs), String)Registers a subscriber to the QueueItemAvailable event.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodUnregisterForQueueItemArrivedUnregisters a subscriber to the QueueItemArrived event.
Public methodUnregisterForQueueItemAvailableUnregisters a subscriber to the QueueItemAvailable event.

Public eventQueueItemArrivedOccurs when an item is delivered on this WorkflowQueue.
Public eventQueueItemAvailableOccurs when an item is available on this WorkflowQueue.

Workflow queues are used to pass messages between a host or host services and activities in a workflow. Any activity can create a WorkflowQueue by calling WorkflowQueuingService.CreateWorkflowQueue, and a host, a service, or another activity can call Enqueue to add an item to that WorkflowQueue. You can subscribe to the QueueItemAvailable event to be notified when an item arrives on the WorkflowQueue. You can use Peek to examine an item at the beginning of the WorkflowQueue and Dequeue to remove an item from the WorkflowQueue. Each WorkflowQueue is associated with a WorkflowQueuingService that you can use to perform other management operations on the WorkflowQueue, such as deleting the queue. QueuingService exposes the WorkflowQueuingService associated with this WorkflowQueue.

The following code example demonstrates how you can create a WorkflowQueue by calling the WorkflowQueuingService.GetWorkflowQueue method. It also uses the Count property to determine whether any messages exist in the current queue. Finally, the code uses the Dequeue method to remove and return the first object in the queue.

This code example is part of the File Watcher Activity SDK Sample from the FileSystemEvent.cs file. For more information, see File System Watcher Activity.

Private Function ProcessQueueItem(ByVal context As ActivityExecutionContext) As Boolean

    Dim qService As WorkflowQueuingService = context.GetService(Of WorkflowQueuingService)()

    If Not qService.Exists(Me.QueueName) Then
        Return False
    End If

    Dim Queue As WorkflowQueue = qService.GetWorkflowQueue(Me.QueueName)

    ' If the queue has messages, then process the first one
    If Queue.Count = 0 Then
        Return False
    End If

    Dim e As FileWatcherEventArgs = CType(Queue.Dequeue(), FileWatcherEventArgs)

    ' Raise the FileSystemEvent
    MyBase.RaiseGenericEvent(Of FileWatcherEventArgs)(FileSystemEvent.FileWatcherEventHandlerEvent, Me, e)
    DoUnsubscribe(context, Me)
    Return True
End Function

.NET Framework

Supported in: 4, 3.5, 3.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.