Simple Workflow Designer with Silverlight and MEF

Introducing simple workflow designer

I’m excited to announce another project from my collection went public today. This time it is a demo POC (proof of concept) implementation for a simple workflow designer written in Silverlight 4 and MEF.


The project contains the following features that may be interesting for review:

  • Design surface with drag and drop (MVC)
  • Toolbox with automatic runtime discovery of items (MVVM)
  • Drawing connections, live update of connections during drag and drop
  • Separate model layer with custom serialization support (functions, activities, workflows)
  • Separate presentation layer (visual elements for activities), styling and templating nodes
  • Runtime discovery of models and corresponding node views (decoupled layers)
  • Simple rules (i.e. “Output ” node may have only 1 incoming connection)

There are two modes supported out of box – Design and Source views.

Design view

This mode showcases the process of visual modeling. The process is divided into two separated areas – Toolbox and Design Surface.


Toolbox hosts all items exported and discovered at runtime by means of MEF. Default set of activities resides in a separate “WorkflowDesigner.Activities.dll” assembly and can be easily replaced or extended. There’s also an additional “WorkflowDesigner.Sdk.dll” assembly that is mean to be shared across 3rd party libraries and aids in creating custom activity libraries.

You can add activities to the surface by double-clicking the corresponding item in the toolbox. For the sake of simplicity there is no drag and drop support for the toolbox but it can be easily introduced. The quickest way may be reusing Telerik’s drag and drop manager with fancy visual cues, but this is out of scope of this article.

Design surface is based on MVC pattern and showcases basic set of functions like: drag and drop of activities across the surface, drawing connection lines, removing nodes or connections, clearing entire surface. Every visual node is mapped to underlying model (activity) at runtime. That means that both activity and it’s visual representation are completely decoupled and any of the parts can be easily tuned or extended.

For demonstration purposes default activities emulate the behavior of OData- or SQL-based entities with simple UI editors, entire project emulates the process of creating a workflow that deals with data aggregation.


UI dialogs are not bound to any particular business logic except assigning corresponding property values of the model entity. However this may be a good start building user experiences based on your real-life scenarios.



Source view

In addition the Source view feature is supported. It allows you switching to the XML representation of the workflow at any time during design process. Serialization is completely custom and was kept as simple as possible in order to be replaceable or customized. Based on your real-life scenarios the resulting XML can travel to server side and can be turned into object graph without UI dependencies, etc.


Project structure

I will be giving only brief overview of the project structure in this article. Most of the code is split into 2 areas and resides in 2 different class libraries: “WorkflowDesigner.Sdk” and “WorkflowDesigner.Activities“:



As soon as you figure out the process of creation of new activities you most probably may need only “WorkflowDesigner.Sdk” assembly that contains all core and shared functionality.

Source code

You can grab the source code at my GitHub repository.


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