More on WF: Getting Started

This post was originally published at http://solepano.blogspot.com

1- Quickly create your first sequence workflow

[See my previous post about the requirements for developing .Net framework 3 features.]

I am not going to put many details here, but to create your first workflow you need to select one of the workflow project templates in Visual Studio 2005. Just to start select the Sequential Workflow Console Application template. This generates a project with the references to the WF assemblies, the workflow itself and a test program.

By clicking on the workflow class the workflow is shown in the designer. Here is where you can drag activities from the toolbox. For example drag a CodeActivity. In the CodeActivity ExecuteCode property, type a method's name and press enter. VS will generate the method stub for you. Just write hello world to console there. Pressing the "view code" tab, the partial class with the workflow code (wfl properties, event_handlers, methods, etc) appears. You can see that the workflow inherits from SequentialWorkflowActivity.

So far we have the workflow defined with a set of activities. What we need now is to host the workflow and execute it. The generated program shows us how to do it:

using(WorkflowRuntime workflowRuntime = new WorkflowRuntime()) {

...

WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(WorkflowConsoleApplication1.Workflow1));

instance.Start();

...

}

So, just press F5 and see the greeting message!

2- Get a feel of the Pre-build Activities

Some of the pre-build activities I have been experiencing with:

• CallExternalMethod
• Code
• Delay
• IfElse
• Listen
• Sequence
• HandleExternalEvent

They are more or less self explained...I only want to mention one thing that may be a constraint in some circumstances:

The CallExternalMethod activity needs the following properties to execute:

• InterfaceType
• MethodName
• Parameters

and the HandleExternalEvent similar properties:

• InterfaceType
• EventName
• Parameters

In both cases the InterfaceType must be an Interface decorated with the ExternalDataExchange attribute, only this type of interfaces will be listed by the object browser. So the presence of that attribute is what I think may be a restriction as you can't use just any already built assembly.

3- Pass data to the WF:

There are two general approaches for receiving data into a workflow when it is started. They are Parameters and Events. With parameters, a list of parameter names and types are defined with the workflow. These parameter values are passed in by a host when it starts a new instance of the workflow type. With events, workflow authors add an activity that receives an event and data associated with the event. Events are generally specific to the host and custom activities that have been designed to handle the event.

The parameters can be passed in the CreateWorkflow method as shown here:

using(WorkflowRuntime workflowRuntime = new WorkflowRuntime()) {

...

 

Dictionary<string, object> parameters = new Dictionary<string, object>();
parameters.Add("FirstName", "Tom");
parameters.Add("LastName", "Sawyer");

WorkflowInstance instance = wr.CreateWorkflow(typeof(HelloWorldWorkflow.Workflow1), parameters);
instance.Start();

...

}

4- Make use of Conditions

A rule condition is a condition statement that is created in a dialog and stored as XML with the workflow. It can include predicates that compare workflow state and Boolean algebra combining multiple predicates. The conditions can be used in various activities including IfElse, While, ConditionedActivityGroup, and Replicator.

Take for example the IfElse activity. A condition can be set to one or both of its branches using the activity's properties. You can specify a CodeCondition or a DeclarativeCondition. In the first case you just enter the method's name. When you press enter the condition handler will be generated and shown in the code window. Put your logic in there, for instance:

public void If_Condition(object sender, ConditionalEventArgs e){

e.Result = this.reviewArgs.Review.Approved;

}

When using the DeclarativeCondition, you can use the Condition Editor to create it. You can access the workflow properties by intellisense.