Using Visual Basic .NET to Create a Plug-in

Article
09/04/2009

To create a plug-in using Visual Basic and Microsoft Visual Studio® .NET, complete the following steps:

Start Microsoft Visual Studio .NET and, on the File menu, click New and then click Project.
In the New Project dialog box, click Visual Basic Projects and click the Class Library template. Give the project a name, specify a location for your project, and click OK.
Click Add Reference on the Project menu. Click the .NET tab in the Add Reference dialog box and select the Microsoft.WindowsMediaServices component. Click OK.

Open the Class1.vb file and add the following namespaces.

Imports System
Imports System.Runtime.InteropServices
Imports Microsoft.WindowsMediaServices.Interop
Imports Microsoft.Win32

Declare a class to represent your plug-in object and inherit from the IWMSBasicPluginIWMSBasicPlugin Object (Visual Basic .NET). You must also inherit from the specialized interfaces needed by the type of plug-in you are creating. For example, an event notification plug-in must inherit from the IWMSEventNotificationPluginIWMSEventNotificationPlugin Object (Visual Basic .NET). This is illustrated by the following example.
```
Public Class VBEventTest
    Implements IWMSBasicPlugin
    Implements IWMSEventNotificationPlugin
```
Use the GuidAttribute class in the System.Runtime.InteropServices namespace to add an explicit GUID to the class that represents your plug-in. You can use the GuidGen.exe utility that ships with Visual Studio .NET to generate a GUID.
```
<GuidAttribute("7DF709B2-3585-4201-BC50-4820ABE2BF18")> _
Public Class VBEventTest
    Implements IWMSBasicPlugin
    Implements IWMSEventNotificationPlugin
```

Use the keyword to override the ImplementsIWMSBasicPlugin methods. Your implementation of these methods depends upon the nature of your plug-in. The following example illustrates the minimal implementation.

    Public Sub EnablePlugin( _
            ByRef plFlags As Integer, _
            ByRef plHeartbeatPeriod As Integer) _
                  Implements IWMSBasicPlugin.EnablePlugin

        ' Set the heartbeat period to zero.
        plFlags = 0
        plHeartbeatPeriod = 0
    End Sub

    Public Sub DisablePlugin() _
                  Implements IWMSBasicPlugin.DisablePlugin

    End Sub

    Public Sub InitializePlugin( _
            ByVal pServerContext As IWMSContext, _
            ByVal pNamedValues As WMSNamedValues, _
            ByVal pClassFactory As IWMSClassObject) _
                  Implements IWMSBasicPlugin.InitializePlugin

    End Sub

    Public Sub OnHeartBeat() _
                  Implements IWMSBasicPlugin.OnHeartbeat

    End Sub

    Public Sub ShutDownPlugin() _
                  Implements IWMSBasicPlugin.ShutdownPlugin

    End Sub

    Public Function GetCustomAdminInterface() As Object _
                  Implements IWMSBasicPlugin.GetCustomAdminInterface
        Return 0
    End Function

Override the methods required by the specific type of plug-in you are creating. For example, if you are creating an event notification plug-in, you must override methods in the IWMSEventNotificationPlugin interface. This is illustrated by the following example.

' Overrides the IWMSEventNotificationPlugin.OnEvent method. This 
' implementation displays a message box when a client either
' connects or disconnects.

Public Function GetHandledEvents() As Object _
               Implements IWMSEventNotificationPlugin.GetHandledEvents

    ' Capture the connect and disconnect events.
    Dim iHandledEvents(2) As Integer
    iHandledEvents(0) = WMS_EVENT_TYPE.WMS_EVENT_CONNECT
    iHandledEvents(1) = WMS_EVENT_TYPE.WMS_EVENT_DISCONNECT

    Return iHandledEvents

End Function

Public Sub OnEvent( _
          ByRef pEvent As WMS_EVENT, _
          ByVal pUserCtx As IWMSContext, _
          ByVal pPresentationContext As IWMSContext, _
          ByVal pCommandCtx As IWMSCommandContext) _
                  Implements IWMSEventNotificationPlugin.OnEvent

    Try
        Select Case pEvent.Type
            Case WMS_EVENT_TYPE.WMS_EVENT_CONNECT
                MsgBox("Client connected", _
                       MsgBoxStyle.OKOnly, _
                       "VB Sample Event Plug-in")

            Case WMS_EVENT_TYPE.WMS_EVENT_DISCONNECT
                MsgBox("Client disconnected", _
                       MsgBoxStyle.OKOnly, _
                       "VB Sample Event Plug-in")
            End Select

    Catch e As Exception
        MsgBox(e.ToString, MsgBoxStyle.OKOnly, "OnEvent Error")

    End Try

End Sub

Create functions that modify the registration process so that Windows Media Services can find your plug-in. You can use the Regasm.exe utility that ships with Visual Studio .NET to register an assembly, but Windows Media Services requires more information about your plug-in than it can find in the registry settings created by Regasm. However, Regasm can call additional methods implemented by your plug-in to supply extra information to the registry. You can use the ComRegisterFunctionAttribute and the ComUnregisterFunctionAttribute classes to identify the appropriate methods to call, and you can use the Registry and RegistryKey classes in the Microsoft.Win32 namespace to create and modify registry keys. This is illustrated for an event notification plug-in by the following example. For more information about registry settings, see Registering Plug-ins.

<ComRegisterFunctionAttribute()> _
Shared Sub RegisterFunction(ByVal t As Type)
  Try
    Dim regHKLM As RegistryKey
    regHKLM = Registry.LocalMachine
    regHKLM = regHKLM.CreateSubKey("SOFTWARE\\Microsoft\\Windows Media\\Server\\RegisteredPlugins\\Event Notification and Authorization\\{7DF709B2-3585-4201-BC50-4820ABE2BF18}")
    regHKLM.SetValue(Nothing, "Sample VBEvent Notification")

    Dim regHKCR As RegistryKey
    regHKCR = Registry.ClassesRoot
    regHKCR = regHKCR.CreateSubKey("CLSID\\{7DF709B2-3585-4201-BC50-4820ABE2BF18}\\Properties")
    regHKCR.SetValue("Name", "Sample VBEvent Notification")
    regHKCR.SetValue("Author", "XYZ Corporation")
    regHKCR.SetValue("CopyRight", "Copyright 2002 . All rights reserved")
    regHKCR.SetValue("Description", "Enables you to trap the connect and disconnect events")

  Catch e As Exception
    MsgBox(e.Message, MsgBoxStyle.OKOnly)
  End Try
End Sub

<ComUnregisterFunction()> _
  Shared Sub UnRegisterFunction(ByVal t As Type)
    Try

      Dim regHKLM As RegistryKey
      regHKLM = Registry.LocalMachine
      regHKLM.DeleteSubKey("SOFTWARE\\Microsoft\\Windows Media\\Server\\RegisteredPlugins\\Event Notification and Authorization\\{7DF709B2-3585-4201-BC50-4820ABE2BF18}")

      Dim regHKCR As RegistryKey
      regHKCR = Registry.ClassesRoot
      regHKCR.DeleteSubKeyTree("CLSID\\{7DF709B2-3585-4201-BC50-4820ABE2BF18}")
      regHKCR.DeleteSubKeyTree("VBEventTest.VBEventPlugin")

    Catch e As Exception
      MsgBox(e.Message, MsgBoxStyle.OKOnly)
    End Try
End Sub

Build your plug-in. You can register the assembly manually or by using Visual Studio. To register the assembly manually, copy it to <%systemroot%>/system32/windows media/server, and run the Regasm.exe utility to register it and create a type library.
```
    regasm VBEventTest.dll /tlb
```

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Using Visual Basic .NET to Create a Plug-in

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