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CHAPTER 1
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Building a Simple Workflow
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Let s start by building a simple workflow. Start Visual Studio (VS) 2010 and select the New Project link. Under the Installed Templates, navigate to Visual C#, Workflow and you should see that four templates have been provided. Select the Workflow Console Application, as shown in Figure 1-1. Enter the name as 01 and select a suitable location for this solution.
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Figure 1-1. Creating a new workflow project
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CHAPTER 1 BUILDING A SIMPLE WORKFLOW
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A Simple Workflow
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The template generates a Program.cs file, which implements the console application. It also generates a Workflow1.xaml file, which defines the activities in your workflow. If you ve worked with Windows Presentation Framework (WPF) applications, you re probably familiar with xaml, which is an XML-like syntax used for declaring programmatic elements. Instead of labels, text boxes, and grids, however, this file will contain the activity-derived elements in your workflow definition. VS 2010 provides a designer that allows you to graphically view and edit these activities.
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Exploring the IDE
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Figure 1-2 shows a typical layout of the Visual Studio 2010 integrated development environment (IDE). The Toolbox on the left contains the built-in and custom activities that are available to you. I have expanded some of the more common groups of activities. The Solution Explorer and the Properties window are on the right. The bottom window contains a number of tabs including the Error List and Output window.
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Figure 1-2. Typical Visual Studio 2010 IDE
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CHAPTER 1 BUILDING A SIMPLE WORKFLOW
The WF 4.0 designer is in the middle. At the bottom right, there are controls for zooming. Workflow designs in version 4.0 tend to be somewhat long, and this is a handy feature to see the big picture or to find a particular activity. There are three controls at the bottom left for displaying the variables, arguments, and imported assemblies. When you click the Variables control, a window appears to show the existing variables, as shown in Figure 1-3. To close this window, click the Variables control again.
Figure 1-3. Viewing workflow variables If you think of your workflow as a class, variables are the class members. You can use them to store data that must be shared between activities. You can define the scope of a variable either the entire workflow or just a specific activity (and its children). Arguments are similar to variables, but they are intended for passing data in or out of the workflow. You can think of them as method parameters. Figure 1-4 shows what the Arguments window looks like. Notice the Direction column; it defines whether the data is passed in to the workflow or sent out of the workflow.
Figure 1-4. Viewing workflow arguments
Designing the Workflow
The initial workflow designer is empty. You will drag activities onto it to define the workflow behavior. This project will initially just display the greeting Hello, World! Later, you ll embellish it somewhat to discover some of the procedural activities. To start, drag a Sequence activity onto the designer. Then drag a WriteLine activity to the Sequence. The diagram should look like the one shown in Figure 1-5.
CHAPTER 1 BUILDING A SIMPLE WORKFLOW
Figure 1-5. Adding a WriteLine activity The Properties window is shown in Figure 1-6.
Figure 1-6. WriteLine Properties window The DisplayName property is the text shown in the diagram. You should give this a more meaningful name because when you have many WriteLine activities, it will help you remember what this is for. Change this to Hello. Also, enter the Text property as the following literal string: "Hello, World!" The Text property can be any expression that results in a string. You can click the ellipses, which will display a dialog in which you can enter an expression. You can leave the TextWriter property blank. By default, the text will be written to the console. You can specify a class derived from TextWriter (new for .Net 4.0) if you want to specify a different implementation. This will be demonstrated in 9.
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