The Problem Solver

Note: This blog post is written using the .NET framework 4.0 Beta 2

Flowcharts are a nice addition to Windows Workflow Foundation 4. They allow for a lot of pretty complex behavior that is hard to do in a sequential workflow. In WF 3 we used to model these complex behaviors as state machine workflows. That worked but they weren't really state machines or event driven and things could get a bit tricky.

Enter the flowchart in Windows Workflow Foundation 4

One of the good things is that a flowchart is not another workflow type. No it is just another activity to drop in a workflow. So you are free to combine sequential work with a flowchart in one workflow. For example you can have a Sequence activity containing a Flowchart activity and that in turn can contain another Sequence activity which can contain another …. I guess you get the picture.

Below a Flowchart containing a mix of a FlowSwitch and a FlowDecision activity, which are only usable in a Flowchart, and some other general activities like a WriteLine and an Assign activity.

So far so good.

The one thing I don’t like is the FlowSwitch activity

The problem with the FlowSwitch is that the activity takes an expression determining the branch to execute and each branch has a case property to determine which branch is executed. Sounds like a good plan except when you start trying things. What I did was add a Random variable named rnd to the workflow so different branches would execute. To do this I added the following expression to the FlowSwitch:

rnd.Next(5)

Next in each of the first 3 cases I entered 1, 2 and 3 leaving the 4th as default. Sounds good right?

Well not quite!

When I ran the sample I would only get Default printed to the console. Well I guess with Random that is possible to try again. And again.

Hmm something must be wrong here.

It turns out all the cases are of type string and the expression is of type Int32. Those are never going to match! But there are no compile or runtime errors either. I am sure this is going to bite me some time in the future

Of course the FlowSwitch should just to a ToString() on the expression result, anything else would be pointless as any comparison fails. But as it doesn’t we have to do so ourselves. So I changed the Expression to:

and everything works as expected.

Enjoy!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Note: This blog post is written using the .NET framework 4.0 Beta 2

When using Windows Workflow Foundation 4 you often need to enter expression in some activity property. The new thing is these expressions are all in the Visual Basic dialect regardless of what language you project is in. So when developing a project in C# the expressions are sill in Visual Basic.

Weird right?

Well not really when you think about it!

After all power business users are expected to be able to modify workflows. And guess what their favorite tools are. That would be Microsoft Excel and Word. And what do they use to create macros? Right Visual Basic for Applications is their language of choice.

So if they use VBA letting them enter VB into expression dialogs is a far more natural fit than having them use C#.

A case for the Delay activity

So lets take a look at the delay activity. This activity takes 1 input property Duration of type Time Span. So I guess that means our VBA power users are going to have to enter something like if they want to wait 5 seconds:

Now for some reason I suspect that is not the first thing they are going to type. In fact they are more likely to time something like “0:0:05” instead. Not very VB like right?

Well it turns out workflow is smart enough to realize it can convert the string literal to a Time Span and use this. So when our power users does the following it just works

Nice, I like this!

Enjoy WF4!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Op 21 november 2009 organiseren de SDN, de dotNED User Group en VBcentral.nl samen de derde Nederlandse Code Camp. Een unieke dag, voortkomend uit een unieke samenwerking. Kenmerkend aan deze dag is, dat het een evenement is dóór ontwikkelaars en vóór ontwikkelaars!

We zijn op zoek naar collega ontwikkelaars die het leuk vinden om ook een sessie voor hun rekening te nemen. Er is ruimte voor de meer traditionele sessies, maar bijvoorbeeld ook voor Chalk & Talk sessies. In principe is zijn de mogelijke onderwerpen zeer divers en worden door ons op voorhand niet beperkt. Ben jij geïnteresseerd om ook een sessie te doen? Laat het ons weten! Ook als je geen of nog niet zoveel sprekerservaring hebt ben je meer dan welkom. Indien je dat wilt willen we je hier best mee helpen.

Het evenement vindt plaats in Rotterdam en meer informatie kun je vinden op de Code Camp website:www.codecamp.nl

We zien graag jouw sessievoorstel tegemoet! Stuur deze zo snel mogelijk naar: andre@obelink.com.

Een lijstje van onderwerpen waar deelnemers ondermeer om vragen:

• Architectuur/Design patterns
• Frameworks
• Surface
• .NET 4/3.5
• Visual Studio 2010
• VSTS
• Open Source
• SharePoint
• ASP.NET/MVC/Web development/Silverlight
• Windows 7
• iPhone
• DNN
• VSTO
• LINQ
• SQL Server 2008
• Geneva
• BizTalk
• Windows Presentation Foundation
• Windows Communication Foundation
• Windows Workflow Foundation

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Note: This blog post is written using the .NET framework 4.0 Beta 2

Creating parameters for a workflow is quite easy to do in WF 4. Just open the arguments tab in the workflow and add each input or output parameter you need and the required type.

Now in WF 3 passing data to a workflow was done using a Dictionary<string, object> to specify the input. This is very flexible but also very brittle as it is all magic of key names matching property names. This approach still works as the following code demonstrates.

var input = new Dictionary<string, object>();

input["FirstName"] = "Maurice";

input["LastName"] = "de Beijer";

var result = WorkflowInvoker.Invoke(new Workflow1(), input);

Console.WriteLine(result["Greeting"]);

However WF4 has a new approach that includes full type safety. Every time you create an in or out argument the workflow will also get a corresponding public property. These properties are of type InArgument<T> but they contain an implicit cast from T so the code is quite easy as shown below.

var workflow = new Workflow1();

workflow.FirstName = "Maurice";

workflow.LastName = "de Beijer";

var result = WorkflowInvoker.Invoke(workflow);

Console.WriteLine(result["Greeting"]);

Much cleaner!

Unfortunately the OutArgument Greeting is there but printing it’s contents to the console only results in the type being printed. There is also a Get() method but this requires an ActivityContext to be passed. So in the case of output we are still restricted to using the Dictionary<string, object>.

Enjoy!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

One real nice feature in Windows 7 is the boot from VHD capability. Real simple to do once you know the basics. And these basics are all covered in 2 blog posts by Scott Hanselman. So rather that repeat the information I am just going to point to his blog posts.

1. Step-By-Step: Turning a Windows 7 DVD or ISO into a Bootable VHD Virtual Machine
2. Less Virtual, More Machine - Windows 7 and the magic of Boot to VHD

Enjoy!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

www.twitter.com/mauricedb

Op 21 november 2009 organiseren de SDN, Stichting dotNed en VBcentral samen het derde Nederlandse Code Camp. Dit is een dag lang met code, code sharing, freaking en gezellig samenzijn. Een evenement door ontwikkelaars, voor ontwikkelaars. De regie ligt voor een belangrijk deel bij de deelnemers! Het aantal plaatsen voor deelnemers is wel beperkt tot maximaal 150. Wacht dus niet te lang met beslissen want voor je het weet is er geen plaats meer. Vergeet bij je aanmelding niet op te geven welke onderwerpen je interesse hebben. Bovendien nodigen we iedereen graag uit om zelf een sessie in te vullen.

Op de website, www.codecamp.nl, vind je meer informatie en kan je je aanmelden.

Looking for the slides and samples from my two presentations at the Nationale Office Dag in Ede? You can download them from here.

Enjoy!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu