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for input), and a bookmark must be defined to mark the current execution point in the workflow.

Persistence is particularly important when you have long-running workflows, where you want to be

able to unload workflows that are idle and waiting for input, or if the machine/server may restart in

the times that the workflow is idle, or if the execution may even continue on a different server (such

as in a server farm).

Note that the workflow itself is not persisted to the instance, only its state. You

need to be aware of the consequences of modifying the workflow while instances

are still alive and persisted, and cater accordingly.

WF comes with a default persistence provider called SqlWorkflowInstanceStore that handles

persisting a workflow instance to a SQL Server database. You can also create your own custom

persistence provider by inheriting from the InstanceStore class.

You have two ways to persist a workflow instance. One is to use the predefined Persist activity from the

Toolbox in your workflow, which will persist the workflow instance when executed by the run time.

The other option is for the host to register an event handler for the PersistableIdle event, which

is raised by the run time when the workflow instance is idle (but not yet complete). The host can then

choose whether or not to persist the workflow instance, returning a value from the PersistIdleAction

enumeration that will tell the run time what it should do.

tracking

WF enables you to implement tracking in your workflows, where various aspects of the execution

of a workflow can be logged for analysis. Tracking provides transparency over your workflow,

enabling you to see what it has done in the past and its current execution state by the workflow run

time emitting tracking records.

You can specify the granularity at which the tracking records will be emitted by configuring a

tracking profile, which can be defined either in the App.config file or through code. This will

enable you to specify which tracking records you want the workflow run time to emit. The types of

tracking records that can be emitted include workflow life cycle records (such as when a workflow

starts or finishes), activity life cycle records (such as when an activity is scheduled or completes, or

when an error occurs), bookmark resumption records, and custom tracking records (which you can

emit from your custom activities). These tracking records can include associated data, such as the

current values of variables and arguments.

Where tracking records are written is determined by specifying a tracking participant. By default,

the WF run time emits tracking records to the Windows Event Log. You can create your own

Getting started .

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tracking participants if you, for example, want to write tracking records to a different source,

such as a database.

You can also trace the execution of a workflow for troubleshooting and diagnostic purposes, which

makes use of the standard .NET trace listeners. Tracing can be configured in the App.config file.

GettinG started

Start by opening the New Project dialog and navigating to the Workflow category under your

favorite language (as shown in Figure 32-1).

fiGure 32-1

As you can see, you have four project types to choose from as follows:

.

Activity Designer Library: Enables you to create and maintain a reusable library of activity

designers to customize how their corresponding activities look and behave in the WF

designer.

.

Activity Library: Creates a project that enables you to create and maintain a reusable library

of activities (consisting of other activities) that you can then use in your workflows. Think

of it much like a class library but for workflows.

.

Workflow Console Application: Creates an empty workflow hosted in a console application.

.

WCF Workflow Service Application: Creates a workflow hosted and publicly exposed as a

WCF service.

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For the sample project, you will use the simplest option to get up

and running, by using the Workfl ow Console Application project

template. As you can see from Figure 32 - 2, the project it generates is

very simple, containing Program.cs / Module1.vb and Workflow1

.xaml . The Program class (for C# developers), or Module1 module

(for VB developers), as found in any console application, contains

the entry point for the application (that is, the static/shared Main

method), which is automatically confi gured to instantiate and execute

the workfl ow. The Workflow1.xaml fi le is the fi le where you will

defi ne your workfl ow.

fiGure 32 - 2

You aren ’ t limited to hosting workfl ows in a console application or WCF

service — you can also host them in other platforms such as Windows Forms,

WPF, or ASP.NET applications. Add a workfl ow to an existing project using the

Add New Item dialog and selecting Activity from the Workfl ow category (there is

no Workfl ow item, because a workfl ow is essentially an activity itself, containing

other activities).

Note that the workfl ow fi le is a XAML fi le — a fi le format you may recognize

because it is used to defi ne user interfaces in WPF and Silverlight. However, in

this case it is used to declaratively defi ne a workfl ow. You can view and edit the

underlying XAML for a workfl ow by right - clicking the fi le and selecting View

Code from the context menu.

Before you do anything else, compile and run the application as is to see the result. You should fi nd

that a console window briefl y appears before the application automatically ends (because it is not

currently confi gured to actually do anything).

The name Workflow1.xaml isn ’ t very meaningful, so you will no doubt want to change that to

something more appropriate. Unfortunately Visual Studio doesn ’ t help you much in this respect

(unlike with forms and classes), because changing the fi lename will not automatically change the

class created behind the scenes for the workfl ow, nor will it change any references to the class when

you change its name in the designer. For example, to rename the workfl ow and its corresponding

class to SimpleProcessWorkflow , you will need to:

Change the name of the fi le (in t . he Solution Explorer).

. Change the name of the corresponding class (by clicking the design surface, and assigning

the name to the Name property in the Properties tool window).

. C hange all existing references to the workfl ow class. In this case where you haven ’ t done

anything with your project as yet, the only reference will be in the Program class (for

C# developers) or Module1 module (for VB developers), which will need to be updated

The Workflow foundation Designer .

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accordingly. Note that the class name will not appear in IntelliSense and will indicate an

error when you enter it, if you have not compiled the project after changing the class name

(because it’s only then that the compiler will regenerate the class).

the workflow foundation desiGner

The WF designer enables you to drop control flow activities and standard activities (from the

Toolbox) on a workflow design surface, and connect them to form the workflow. It’s much like

building a form where you drop controls from the Toolbox onto the design surface, but in this case

you are building a workflow. When you first create the project, the empty workflow is displayed in

the designer, as shown in Figure 32-3.

fiGure 32-3

At the bottom of the designer, you will note the three hyperlink buttons: Variables, Arguments, and

Imports. Clicking one of these buttons pops up a pane at the bottom of the designer that will enable

to you modify their respective configurations.

Variables can be defined for use by activities within a given scope (which is defined by a parent activity

to which the variables are attached). Add a variable by simply popping up the Variables pane (as shown

in Figure 32-4), clicking in the area that says Create Variable, and entering a name for it. You can set

the type for the variable by clicking in the Variable Type column and selecting the type from the drop-

down list. If the type that you need doesn’t appear in the list, you can click the Browse for Types item,

which will pop up a dialog enabling you to type in the qualified name of the type, or navigate through

the referenced assemblies tree to find it. Clicking in the Scope column displays a drop-down list that

will allow you to modify the scope of the variable (by selecting the activity it belongs to). This activity

and its child activities will therefore have access to the variable. Clicking in the Default column enables

you to enter an expression (in VB code) that will set the default value of the variable.

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The Arguments pane (as shown in Figure 32 - 5) enables you to defi ne the input and output

arguments for an activity (which enable the fl ow of data in and out of the activity). There are four

types of arguments (that is, argument directions): Input arguments, Output arguments, In/Out

arguments, and Property arguments.

. Input arguments can conceptually be considered the same as passing parameters into

methods by value in regular code.

. Output arguments can conceptually be considered the same as output parameters in

methods in regular code, whose values are set in the method and returned to the caller.

. In/Out arguments can conceptually be considered the same as passing parameters into

methods by reference in regular code.

. Property arguments can conceptually be considered the same as assigning property values

on an object in regular code.

Add an argument by simply popping up the Arguments pane, clicking in the area that says Create

Argument, and entering a name for it. Specify the type of argument by clicking in the Direction

column and selecting a type from the drop - down list. You can set the type for the argument by

clicking in the Argument Type column and selecting the type from the drop - down list. As with

variables, you can also assign an expression to the default value of the argument (for In and

Property arguments only).

fiGure 32 - 4

Note that the default value column accepts expressions rather than values. If you

want to assign a value to the variable rather than an expression you will need to

enter the literal value, not simply the value itself. The literal values for numeric

values are identical, but if the variable is a string, you will need to enclose it in

double quotes. This also applies when setting the default value of arguments.

Note that activities can also have a return value.

The Workflow foundation Designer .

711

fiGure 32-5

The Imports pane (as shown in Figure 32-6) enables you to import namespaces (the same as defining

using statements in C#) for use in expressions. At the top of the panel is a combo box where you can

type a namespace to import and add to the list, or select a namespace from the drop-down list.

fiGure 32-6

Workflows can become quite large and potentially unwieldy as they increase in complexity, but

luckily the WF designer contains a few tools to help you manage and navigate through the model.

You will find that some activities have an icon in their top-right corner, enabling you to roll them

up to just display their title (that is, collapse them), or to expand them if they are collapsed. Because

you can nest activities within activities (and so on), potentially creating rather deep and complex

hierarchies, it can be useful to hide some of this complexity by collapsing activities when you are

not actively editing them. Collapsing activities can reduce the amount of space they take in the

workflow diagram, and can also be used to hide the complexity of the hierarchy of sub-activities

contained within them. You can then expand the activities again by clicking this same icon (whose

arrows will have changed direction according to the state of the activity).

In the top-right corner of the designer, you will find an Expand All hyperlink button and a Collapse

All hyperlink button (both of which change to read Restore when clicked). It can often be useful to

“roll up” the entire workflow (using the Collapse All hyperlink button) to its top-level activities, from

which you can then drill down through specific activities by expanding them as required to follow a

specific logical path. In addition, you can also use the Expand All hyperlink button to expand all the

activities that form the workflow, enabling you to get a picture of the full extent of the workflow.

You can zoom in and out of the view of the workflow using the drop-down list in the bottom-right

side of the designer (that lists zoom percentages), and clicking the magnifying glass icon to its left

resets the view back to 100%. The icon to the right of the drop-down list will automatically select

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a zoom level that will enable the entire workflow to be fitted within the visible area of the designer

window (without requiring you to scroll).

When you have a large workflow with activities you don’t want to collapse, with it far too big to

fit entirely in the visible area of the designer window, you can make use of the Overview window by

clicking the rightmost icon in the bottom-right side of the designer. This will pop up a window in

the designer (as shown in Figure 32-7) that enables you to pan around the workflow by clicking

and dragging the orange rectangle (representing the visible portion of the workflow in the designer)

around to display the part of the workflow that you want to currently view.

fiGure 32-7

As previously discussed, one of the advantages of using WF is that the diagram of the workflow can

be used as a form of documentation for your business process/logic/rules. It can often be useful to

place this diagram in documentation or presentations, and the way to do this is quite easy. Right-

click anywhere on the design surface. Two items appear in the context menu that you can use for

this purpose: Save as Image and Copy as Image. Selecting the Copy as Image menu item copies a