CallExternalMethod Activity in Workflow

Introduction

The CallExternalMethod Activity define a Workflow communication activity that is used to call a method on a local service. This activity is used send data from the Workflow to the host through a local service. A local service is a class which are implements a local service interface and added to the ExternalDataExchangeService. The ExternalDataExchangeService is define as

It comes under the namespace "System.Workflow.Activities"
The instance of this class is added to the workflow runtime engine for local services communications to be enabled.

Step 1 : Open Visual Studio.

Select File->New->Project.
Select Sequential Workflow Console Application.
Workflow1.cs [Design] open.

Step 2 : Go to the Toolbox.

Drag CallExternalMethod Activity.

Step 3 : Go to Solution Explorer and right-click.

Add-> New Item.
Select Interface and Add.
Define [ExternalDataExchange]
Add the namespace Using System.Workflow.Activities.

Code :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Workflow.Activities;
namespace call1
{
[ExternalDataExchange]
interface Interface1
{
void WorkFlowToHost(string msg);
}
}

Step 4 : Go to Solution Explorer and right-click.

Add-> New Item->Class.
Implements Interface.
Add Event.

Code :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Workflow.ComponentModel.Compiler;
using System.Workflow.ComponentModel.Serialization;
using System.Workflow.ComponentModel;
using System.Workflow.ComponentModel.Design;
using System.Workflow.Runtime;
using System.Workflow.Activities;
using System.Workflow.Activities.Rules;
namespace call1
{
class Class1 : Interface1
{
public event EventHandler<SenddataEventArg> RaiseEventFromHost;
public void WorkFlowToHost(string msg)
{
SenddataEventArg arg = new SenddataEventArg();
arg.Response = msg;
EventHandler<SenddataEventArg> Senddata = this.RaiseEventFromHost;
if (Senddata != null)
{
Senddata(this, arg);
}
}
}
public class SenddataEventArg : EventArgs
{
string _response;
public string Response
{
get { return _response; }
set { _response = value; }
}

}
}

Step 5 : Go to Workflow1.cs option.

right-click on CallExternalMetod Activity.
Go to properties option.
Define Interface Type, MethodName.

Step 6 : Double-click in CallExternalMethod Activity.

Write a code.

Code :

using System;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Collections;
using System.Linq;
using System.Workflow.ComponentModel.Compiler;
using System.Workflow.ComponentModel.Serialization;
using System.Workflow.ComponentModel;
using System.Workflow.ComponentModel.Design;
using System.Workflow.Runtime;
using System.Workflow.Activities;
using System.Workflow.Activities.Rules;
namespace call1
{
public sealed partial class Workflow1 : SequentialWorkflowActivity
{
private string _message = "Hey, passingthe data from workflow to host application";
public string Message
{
get
{
return _message;
}
}
public Workflow1()
{
InitializeComponent();
}
private void callExternalMethodActivity1_MethodInvoking(object sender, EventArgs e)
{
}
}
}

Step 7 : Define the Message for CallExternalMethod Activity.

Go to properties option and click in msg option.
Add Message.

Step 8 : Go to Solution Explorer.

Select Program.cs option.
Double-click on option.
Add the Instance of " ExternalDataExchange" class to the WorkflowRuntime.

Code :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Workflow.Runtime;
using System.Workflow.Runtime.Hosting;
using System.Workflow.Activities;
namespace call1
{
class Program
| {
static void Main(string[] args)
{
using (WorkflowRuntime workflowRuntime = new WorkflowRuntime())
{
ExternalDataExchangeService externalService = new ExternalDataExchangeService();
workflowRuntime.AddService(externalService);
Class1 comm = new Class1();
externalService.AddService(comm);
AutoResetEvent waitHandle = new AutoResetEvent(false);
workflowRuntime.WorkflowCompleted += delegate(object sender, WorkflowCompletedEventArgs e) { waitHandle.Set(); };
workflowRuntime.WorkflowTerminated += delegate(object sender, WorkflowTerminatedEventArgs e)
{
Console.WriteLine(e.Exception.Message);
waitHandle.Set();|
};
WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(call1.Workflow1));
instance.Start();
comm.RaiseEventFromHost += delegate(object sender, SenddataEventArg e)
{
string val = e.Response;
Console.WriteLine(val);|
};
Console.ReadLine();
waitHandle.WaitOne();
}
}
}
}

Step 9 : Press F5 and run the application.