Writing Your First Service in Visual Basic 2008 (part 1)

With the Visual Studio 2008 Visual Basic templates, you can quickly and easily get started with the first service. Begin by opening Visual Studio 2008. If you are launching Visual Studio for the first time, you can select the Visual Basic Settings in the Settings dialog box that appears automatically if you want to set help filters and keyboard shortcuts to Visual Basic.

From the File menu, select New Project. For the Project Type, expand Visual Basic and then select Windows. In the Templates pane, select Windows Service. In the Name text box, type Tutorials. Verify that you have the .NET 3.5 SDK selected in the drop-down box above the Templates pane, and then click OK.

Note

If you are using the Express version of Visual Studio Basic, the Windows Service template may not be available to you. You can look on Microsoft’s MSDN site for templates or download the Professional version.

In the Solution Explorer, you will see Tutorials, under which you will then see My Project and then Service1.vb. Service1.vb holds the wizard-generated code that holds the required components, methods, and entry points to create and compile your service. Currently it is empty except for stubs for the <OnStart> and <OnStop> methods.

Renaming Our Project Files

Now that we have wizard-generated code ready, we want to properly identify the service and rename the wizard-generated labels. Service1.vb represents the service. For this reason, rename the Service1.vb file Tutorials.vb. At this point, the solution, the project, and the service should all be named Tutorials.

Note

Understanding the Wizard Code

Let’s start by reviewing the code generated by the wizard. Right-click the Tutorials.vb file and select View Code. You will see the class definition along with two methods, <OnStart> and <OnStop>. They are both blank, but they are both required for your service to run properly.

The <OnStart> Method

The <OnStart> method represents the entry point into your service. This is what the underlying Service Control Manager (SCM) will call when the user clicks Start on the Control Panel Services screen. You will notice that <OnStart> has one argument. This argument contains the parameters defined in the Administrative Tools, Services, Service Properties. This is where the application is started and also where we will later add functionality that will make the service useful.

The <OnStop> Method

The <OnStop> method represents the exit point of your service. This is where we want to add cleanup code. It will be called when the user clicks Stop on the Services tab under Administrative Tools.

Other Events

Services support more than just the <OnStart> and <OnStop> events. Two other very important events are <OnPause> and <OnContinue>.

<OnPause> allows a user to temporarily suspend operation of your service without shutting it down. At times you might want to debug your service or you might need to perform an action on a server that your service relies on. Allowing it to run while you perform your maintenance could be detrimental. If your service supports <OnPause>, you should implement the method to react to the pause event.

To use the OnPause and OnContinue methods, you must first enable these features in your service by following these steps:

Adding <OnPause>

In the Solution Explorer, right-click the Tutorials.vb and select View Code.

Below the current <OnStop> method, type Protected Overrides Sub <OnPause> and select Enter. As you type this, you should notice that the options for different methods to override appear in the IntelliSense.

You will notice that a single piece of code, <MyBase.OnPause()>, will appear in your method definition. This allows your service to call the base class just in case you have implemented some general code in it. Since we have not, you can remove this code by highlighting it and deleting it. We will not be adding any code to this method at this time.

Adding <OnContinue>

<OnContinue> is the counterpart to <OnPause>. Once a service is paused it will need to be resumed. This is where <OnContinue> comes in. As we did with <OnPause>, we will add this method by typing in the following code below the <OnPause> method: Protected Overrides Sub OnContinue. Now click Enter. Once again you will see its implementation appear with the <Mybase.OnContinue()> code. Again, merely highlight this and delete it.

Now we will create the code to make the service useful.