Datasheet

Chapter 1: Workﬂ ow Programming Principles

3. It then invokes the GetWorkflowQueue method to access the WorkflowQueue object that

represents the workflow queue that the activity created in its initialization phase. Note

that the method passes the QueueName property of its second argument into the

GetWorkflowQueue method. This is not important in our case because this activity creates a

single workflow queue in its initialization phase. However, in cases where the activity creates

more than one workflow queue in its initialization phase, you should use the QueueName

property to ensure that you ’ re accessing the right workflow queue.

WorkflowQueue workflowQueue =

workflowQueuingService.GetWorkflowQueue(e.QueueName);

4. The method then invokes the Dequeue method on the WorkflowQueue object to access the

deposited data, and consumes it:

object data = workflowQueue.Dequeue();

5. The WorkflowQueue_QueueItemAvailable method is part of the execution logic of our activity

because it was the Execute method of our activity that registered this method as an event

handler for the QueueItemAvailable event of the workflow queue. Once the event handler is

registered, our activity can resume its execution where it left off when the external entity finally

deposits the data into the workflow queue. The workflow run time expects every execution

method to notify it when the execution status of the activity changes. Such notification can occur

in two different forms.

If the method returns a value of the ActivityExecutionStatus type, then it must return the appro-

priate ActivityExecutionStatus enumeration value. Otherwise, it must invoke the appropriate

method on the ActivityExecutionContext to inform the workflow run time of the execution sta-

tus change. Execution methods such as Execute, Cancel, and HandleFault return a value of the

ActivityExecutionStatus type. Execution methods such as event handlers do not. In this case, the

WorkflowQueue_QueueItemAvailable method invokes the CloseActivity method on the Activi-

tyExecutionContext to inform the workflow run time that the execution logic of the current ac-

tivity is now completed:

activityExecutionContext.CloseActivity();

The following example presents the complete code for the custom activity that we ’ ve been developing in

last few sections:

using System.Workflow.ComponentModel;

using System.Workflow.Runtime;

using System;

namespace Chapter1

{

public class CustomActivity : Activity

{

protected override void Initialize(IServiceProvider provider)

{

WorkflowQueuingService workflowQueuingService =

provider.GetService(typeof(WorkflowQueuingService))

as WorkflowQueuingService;

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