c# itextsharp create barcode Designing the Workflow in VB.NET

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Designing the Workflow
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You ll start by defining the normal workflow activities and add the error-handling logic later.
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Modifying the Application
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Open the Program.cs file and replace the generated code with the implementation shown in Listing 17-1. Listing 17-1. Implementation of Program.cs using System; using System.Activities;
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CHAPTER 17 COMPENSATION, CONFIRMATION, AND CANCELLATION
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using System.Threading; namespace Wedding { class Program { static void Main(string[] args) { AutoResetEvent syncEvent = new AutoResetEvent(false); WorkflowApplication i = new WorkflowApplication(new Workflow1()); i.OnUnhandledException = (waueea) => { Console.WriteLine("{0} - {1}", waueea.UnhandledException.GetType(), waueea.UnhandledException.Message); return UnhandledExceptionAction.Cancel; }; i.Completed = (wacea) => { syncEvent.Set(); }; i.Run(); syncEvent.WaitOne(); Console.WriteLine("Press ENTER to exit"); Console.ReadLine(); } } public class CallItOffException : Exception { public CallItOffException() : base() { } public CallItOffException(string message) : base(message) { } } } The default action when an unhandled exception is thrown is to terminate the workflow. When this occurs, the cancellation or compensation handlers are not executed. For this project, you must return the Cancel action. This will stop the normal workflow processing, but will allow the cancellation and compensation handlers to perform their defined activities. The WorkflowInvoker class does not give you the ability to override the default action, so you must use the WorkflowApplication class. This file also defines the CallItOffException class that will be used later when the wedding is cancelled:
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CHAPTER 17 COMPENSATION, CONFIRMATION, AND CANCELLATION
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Configuring a TryCatch Activity
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Open the Workflow1.xaml file in design view. Drag a TryCatch activity onto the sequence. The designer should look like the one shown in Figure 17-2. (You used the TryCatch activity in 6 if you want to refer to it for more information.)
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Figure 17-2. An empty TryCatch activity Drag a Sequence activity to the Try section and set the DisplayName to Wedding Preparations. Click the link that says Add new catch and then select Browse for types in the drop-down list. In the dialog, expand the Wedding assembly and choose the CallItOffException class, as shown in Figure 17-3.
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Figure 17-3. Selecting the exception to be caught
CHAPTER 17 COMPENSATION, CONFIRMATION, AND CANCELLATION
Drag a WriteLine activity to the Catches section where it says Drop activity here . For the Text property, enter Catch: + exception.Message. The designer should look like the one shown in Figure 17-4.
Figure 17-4. Completed TryCatch activity
Tip For the Text properties, you will begin the output text with a word that indicates where the activity was executed from. In this case, it was the Catch activity. The remainder of the WriteLine activities will indicate whether the activity was in the Body, Compensation, Confirmation, or Cancellation section. This will help you analyze the results because there are numerous messages being generated.
Using a Parallel Activity
Expand the Wedding Preparations activity and drag a Parallel activity onto it. Set its DisplayName property to Planning Activities. In this workflow, you ll design three sequences of activities that will execute simultaneously. Drag three CompensableActivity objects onto the Parallel activity and set their DisplayName property to Wedding, Reception, and Invitation. The designer should look like the one shown in Figure 17-5.
Figure 17-5. A Parallel activity with three CompensableActivity objects
CHAPTER 17 COMPENSATION, CONFIRMATION, AND CANCELLATION
CompensableActivity
Double-click the Wedding activity. You should have four sections, as shown in Figure 17-6.
Figure 17-6. An empty CompensableActivity As you can see from Figure 17-6, a CompensableActivity allows you to define handlers for compensation, confirmation, and cancellation. The Body section is the normal activity (or sequence of activities) that are executed. If the Body activity must be cancelled before it has completed, the activity in the Cancellation Handler section is executed. The activity in the Compensation Handler section is executed, if necessary, to undo the work of the Body section if the Body has completed. The Compensation Handler section is where you ll define the activity (or sequence of activities) that should be executed if subsequent workflow activities fail and the workflow is aborted. The activity in the Confirmation Handler section is executed when the activity has been confirmed. By default, confirmation happens automatically when the workflow instance has completed. You can place any finalization activities here. The following set of rules may help you remember when these handlers are executed: An activity can be compensated only if it has completed; in-process activities cannot be compensated.
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