Part IV in .NET

Creating QR Code in .NET Part IV

Part IV
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Recognize QR Code In .NET Framework
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Win32 Applications
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Barcode Decoder In .NET
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Required by the Component Designer
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Making QR Code ISO/IEC18004 In Visual Studio .NET
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Private components As System.ComponentModel.Container
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NOTE: The following procedure is required by the Component Designer.
Make Code 3/9 In VS .NET
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It can be modified using the Component Designer.
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UPCE Generation In .NET
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Do not modify it using the code editor.
Generating UPC-A Supplement 5 In None
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Bar Code Creation In Java
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<System.Diagnostics.DebuggerStepThrough()> _
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Private Sub InitializeComponent()
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Encryptor
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Me.CanPauseAndContinue = True
Me.ServiceName = Encryptor"
End Sub #End Region Protected Overrides Sub OnStart(ByVal args() As String) Add code here to start your service. This method should set things in motion so your service can do its work. End Sub Protected Overrides Sub OnStop() Add code here to perform any tear-down necessary to stop your service. End Sub End Class
The preceding code reveals how your service class actually works. The code in the Shared Sub Main procedure creates an array of all the service classes that share the same process space and then passes this array to the ServiceBase.Run shared method:
System.ServiceProcess.ServiceBase.Run(ServicesToRun)
Thanks to this approach, your project can include multiple service classes that run in the same process (and therefore save system resources), yet can be stopped, paused, and resumed independently of one another. A careful examination of the preceding code shows a minor bug in the code generated by the designer. Although the name of the class correctly reflects the Name property you set in the Properties window, the name of the class instantiated in the Shared Sub Main procedure is still Service1 (the statement in boldface in the preceding listing), so you must change it manually as follows:
ServicesToRun = New System.ServiceProcess.ServiceBase() _ {New Encryptor()}
Overriding ServiceBase Methods
A nontrivial service application typically must execute code when the service starts and stops, as well as when the service is paused and resumed (if you set the CanPauseAndContinue property to True). When these events occur, the .NET runtime invokes one of the public methods of the ServiceBase class, so you have to override these methods to execute your custom code instead.
20:
Windows Services
The Encryptor service uses a FileSystemWatcher component to be notified when a new file is created in a given directory on the hard disk. As you saw in 19, you can create this component by means of code or by dropping it from the Components tab of the Toolbox. In our demo Encryptor service, we ll use the latter approach. After you drop an instance of the FileSystemWatcher component on the designer sur face, you should set its EnableRaisingEvents property to False so that the component won t raise events before the service starts. You can leave all the other properties at their default value. Next you can switch to the code editor and add the following code inside the OnStart and OnStop methods:
The path of the watched directory Dim Path As String = C:\Encrypt" Protected Overrides Sub OnStart(ByVal args() As String) Ensure that the directory exists. If Not Directory.Exists(Path) Then Directory.CreateDirectory(Path) End If Start receiving file events. FileSystemWatcher1.Path = Path FileSystemWatcher1.EnableRaisingEvents = True End Sub Protected Overrides Sub OnStop() Stop receiving file events. FileSystemWatcher1.EnableRaisingEvents = False End Sub
Because this service also can be paused and resumed, you should override the OnPause and OnContinue methods as well:
Protected Overrides Sub OnPause() Stop receiving file events. FileSystemWatcher1.EnableRaisingEvents = False End Sub Protected Overrides Sub OnContinue() Start receiving file events. FileSystemWatcher1.EnableRaisingEvents = True End Sub
Implementing the Encryption Algorithm
The Encryptor service sleeps until the FileSystemWatcher component detects that a new file has been created in the directory and fires a Created event. When this happens, the service invokes the EncryptFile custom routine, which reads the contents of the file (in blocks of 8 KB each) and creates a temporary encrypted file with a .$$$ extension. When the encryption is completed, the service deletes the original file and
Part IV
Win32 Applications
renames the temporary file as the original file. The encryption routine simply uses an XOR operation on each byte in the original file with a byte specified in a password:
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