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Generating UPC-A in C#.NET Part I

Part I
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Introducing Windows Workflow Foundation (WF)
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Tip As it happens, Visual Studio can add the handler for you. Nice! Here s how it works: After you type the equal sign (=), press the tab key to let IntelliSense add the EventHandler keyword and name. It will leave the name highlighted. Without changing the highlight, type in the name you want to use (workflowIdled in the preceding example). Then just press the Tab key when Visual Studio prompts you, and Visual Studio will insert the handler with the matching name immediately below whatever procedure you are coding. Of course, you can always modify the handler method name after the handler has been inserted into your code if you need to.
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3. Following the code you just added, type in this line of code to add the handler for workflow completion:
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workflowRuntime.WorkflowCompleted += new EventHandler<WorkflowCompletedEventArgs>(workflowCompleted);
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4. And now add the handler for the WorkflowTerminated event:
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workflowRuntime.WorkflowTerminated += new EventHandler<WorkflowTerminatedEventArgs>(workflowTerminated);
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5. If you compile and run WorkflowHost, the application should compile and execute. But there is no workflow executed because we didn t ask the workflow runtime to start a workflow instance. (We ll add this in the next chapter.) In preparation, though, let s add some code. First, we ll add the automatic reset event we ll need to stop the main thread long enough for the workflow events to fire (so that we can observe them). The AutoResetEvent class is perfect for the job. Following the two lines of code you just typed in (in steps 3 and 4), add these lines of code. (We ll define the waitHandle object in the next step.)
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Console.WriteLine("Waiting for workflow completion."); waitHandle.WaitOne(); Console.WriteLine("Done.");
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6. We ll need to create the _waitHandle object, so add this static class member just prior to the Main method:
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private static AutoResetEvent waitHandle = new AutoResetEvent(false);
7. AutoResetEvent is exported by System.Threading, so add the using directive to the list at the top of the Program.cs source file:
using System.Threading;
8. The three event handlers (created by Visual Studio 2005) both contain not implemented yet exceptions. We need to get rid of those and implement some code. Locate the first handler we added, workflowIdled, and replace the exception you find there with the following lines of code:
Console.WriteLine("Workflow instance idled.");
2
The Workflow Runtime
9. We ll perform a similar edit to the workflowCompleted handler. Replace the not implemented yet exception with this:
Console.WriteLine("Workflow instance completed."); waitHandle.Set();
10. The workflowTerminated handler rounds out the set of handlers. Replace the not implemented yet exception with the code you see here:
Console.WriteLine("Workflow instance terminated, " + "reason: '{0}'.",e.Exception.Message); waitHandle.Set();
The completed main application is shown in Listing 2-2.
Listing 2-2 The Complete WorkflowHost Application
using using using using using System; System.Collections.Generic; System.Text; System.Workflow.Runtime; System.Threading;
namespace WorkflowHost { class Program { private static AutoResetEvent waitHandle = new AutoResetEvent(false); static void Main(string[] args) { WorkflowRuntime workflowRuntime = WorkflowFactory.GetWorkflowRuntime(); workflowRuntime.WorkflowIdled += new EventHandler<WorkflowEventArgs>(workflowIdled); workflowRuntime.WorkflowCompleted += new EventHandler<WorkflowCompletedEventArgs> (workflowCompleted); workflowRuntime.WorkflowTerminated += new EventHandler<WorkflowTerminatedEventArgs> (workflowTerminated); Console.WriteLine("Waiting for workflow completion."); waitHandle.WaitOne(); Console.WriteLine("Done."); } static void workflowTerminated(object sender, WorkflowTerminatedEventArgs e) { Console.WriteLine("Workflow instance terminated, " + "reason: '{0}'.",e.Exception.Message); waitHandle.Set(); } static void workflowCompleted(object sender,
Part I
Introducing Windows Workflow Foundation (WF)
WorkflowCompletedEventArgs e) { Console.WriteLine("Workflow instance completed."); waitHandle.Set(); } static void workflowIdled(object sender, WorkflowEventArgs e) { Console.WriteLine("Workflow instance idled."); } }
What are we missing A workflow to execute! We ll dive into workflow instances in the next chapter. For now, though, if you execute this application, it hangs. Why The events we tapped into never fire because we never execute a workflow instance. That means the event handlers never handle the events. And because of that, waitHandle is never tripped the application hangs forever (or until you terminate it yourself). We ll revisit this application in the next chapter when we add a workflow instance and execute it.
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