Understanding a Hello World program in Windows Workflow Foundation

Hi,

1. Create a new Sequential Workflow Console Application project.

2. Open Workflow1.cs in design mode.

3. Drag a Code activity to the workflow at (Drop activities to create a sequential workflow)

4. Select Code activity and in the properties window for ExecuteCode property write MyMessage and the press enter twice, which will create a method with the same name.

private void MyMessage(object sender, EventArgs e)
{
Console.Write(“Hello World”);
Console.ReadLine();
}

5. Press F5 to run the project.

This completes our first program in windows workflow foundation.

What we have done over here is that

We have created a console application which is hosting a workflow. Workflow requires an application as a host. It could be a console application, windows forms application,

asp.net application and even a Windows service.

We can found the code used for hosting the workflow in Program.cs.

Let’s try to understand the code

// First we are creating an instance of WorkflowRuntime

// WorkflowRuntime – is responsible for starting our workflow, firing events for different situations

// while the task is executing.

using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())

{

// Our application and the workflow, both are running on different threads.

// We need our application to wait long enough before our workflow either gets completed or terminated(due to error).

// For this AutoResetEvent is used.

// Here an instance of AutoResetEvent is created i.e. waitHandle

// calling waitHandle.WaitOne() will make the main thread to wait until it is signalled using

// waitHandle.Set(), which will be done when workflow either gets complete or gets terminated.

AutoResetEvent waitHandle = new AutoResetEvent(false);

 

// Here anonymous method is used to declare an event handler for WorkflowCompleted event

// Once workflow gets completed, the main thread is signalled to proceed further through

// waitHandle.Set()

workflowRuntime.WorkflowCompleted += delegate(object sender, WorkflowCompletedEventArgs e)

{waitHandle.Set();};

 

// Here anonymous method is used to declare an event handler for WorkflowTerminated event

// Once workflow gets completed, the main thread is signalled to proceed further through

// waitHandle.Set(), which releases the console application from its wait

workflowRuntime.WorkflowTerminated += delegate(object sender, WorkflowTerminatedEventArgs e)

{

Console.WriteLine(e.Exception.Message);

waitHandle.Set();

};

 

// Workflow instance is composed of one or more activities. WorkflowRuntime executes these workflow instances.

// workflowRuntime.CreateWorkflow->Creates a workflow instance and if the workflow runtime hasn’t been started

// the CreateWorkflow method calls StartRuntime method of WorkflowRuntime

WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(HelloWorldWorkflow.Workflow1));

 

//Starts the execution of the worflow instance

instance.Start();

 

// The main thread waits till it is signalled to proceed further i.e. waitHandle.Set()

waitHandle.WaitOne();

}

Bye…