Microsoft Visual Basic 2008 : Using the WMI Class

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Adding New EventLog Constants

We will add the constants shown in Listing 1 to the top of the modService.vb file so that we can write the correct EventID to the Application log.

Listing 1. Application log EventID constants.
Public Const WMI_ERROR As Integer = 1010
Public Const WMI_INFO As Integer = 2007
Public Const CONFIG_READ_ERROR As Integer = 4000

Updating <Tutorials.ThreadFunc>

 Listing 2 shows the updated <ThreadFunc> method.

Listing 2. Updated <ThreadFunc> method.
Private Sub ThreadFunc()
   While Not m_ThreadAction.StopThread
     If Not m_ThreadAction.Pause Then
           Dim tmpWMI As New WMI
           If Not tmpWMI.Connect(".") Then
             WriteLogEvent("Thread WMI Connection Error - " +
        tmpWMI.GetError, WMI_ERROR, EventLogEntryType.Error, "Tutorials")
            'Now process the file
             Dim pMOC As ManagementObjectCollection
            'Run our Query for SystemInfo
             pMOC = tmpWMI.Query(Nothing, WMI.Management_Query_Type.SystemINfo)
             If Not pMOC Is Nothing Then
               Dim Name As String = Nothing
               Dim Domain As String = Nothing
               Dim Status As String = Nothing
               Dim NumberOfProcessors As String = Nothing
               Dim TotalPhysicalMemory As String = Nothing
               Dim pMO As ManagementObject
               For Each pMO In pMOC
                   ReadProperty(pMO, "Name", Name)
                   ReadProperty(pMO, "Domain", Domain)
                   ReadProperty(pMO, "Status", Status)
                   ReadProperty(pMO, "NumberOfProcessors",
                   ReadProperty(pMO, "TotalPhysicalMemory",
                Catch ex As Exception
                   Exit For
                End Try
               'Lets Log This Information
                Dim pszOut As String
                pszOut = "Name: " + Name.Trim
                pszOut += ",Domain: " + Domain.Trim
                pszOut += ",Status: " + Status.Trim
                pszOut += ",NumberOfProcessors: " +
                pszOut += ",TotalPhysicalMemory: " +
                TotalPhysicalMemory.Trim + vbCrLf
                WriteLogEvent(pszOut, WMI_INFO,
                EventLogEntryType.Information, "Tutorials")
            WriteLogEvent("Thread WMI query Error - " +
            tmpWMI.GetError, WMI_ERROR, EventLogEntryType.Error,
           End If
         End If
         WriteLogEvent("Thread Function Information - " +
         Now.ToString, 1005, EventLogEntryType.Information,
      Catch tab As ThreadAbortException
     'this must be listed first as Exception is the master catch
     'Clean up the thread here
        WriteLogEvent("Thread Function Abort Error - " +
        Now.ToString, 1006, EventLogEntryType.Error, "Tutorials")
     Catch ex As Exception
        WriteLogEvent("Thread Function Error - " + Now.ToString,
        1005, EventLogEntryType.Error, "Tutorials")
     End Try
    End If
    If Not m_ThreadAction.StopThread Then
    End If
   End While
End Sub


The example shown in Listing 2 allows us to read and then log information about the system that we have queried. One thing you’ll notice about the WMI class is that we used the built-in query for Win32_ComputerSystem; however, because we knew exactly what information we were querying, we could have written the query ourselves to limit the amount of data that was returned. This is a very good idea when you are querying a large number of servers over a network interface. Not only will the amount of data traffic and memory requirements be reduced, but it will also speed up your application.

Adding the WMI Property Reader Method

When we use the WMI class implementation to run our predefined queries, we will be returned an object with a specific set of properties exposed. To manage the reading of these properties, I’ve implemented the code in Listing 3 to facilitate reading the property and returning the value to the calling method. This method will be added to our existing Tutorials.vb class implementation.

Listing 3. WMI property reading method implementation for Tutorials.vb.
Private Sub ReadProperty(ByRef pObject As ManagementObject,
         ByRef pProp As String, ByRef pszStr As String)
            pszStr = pObject.Properties(pProp).Value.ToString
        Catch ex As Exception
            pszStr = ""
        End Try
End Sub

This method attempts to read the value of the property defined in the parameter list called pProp, and setting the outgoing pointer, pszStr, to the string value of the property. If the property is not valid or an exception occurs, the return parameter is assigned a null value.

The previous code was fairly simple. We used a WMI class to connect to the server, and then we queried the WMI class that we wanted information about, assigning the result of that query to our local ManagementObjectCollection. When you call a WMI class using System.Management, nearly every object returns two types of collections: the objectname collection and the Enumerator collection. You can use either collection to access the objects that were returned. When you perform the query, you are returned a ManagementObject-Collection, which contains all the objects from your query, such as each Logicaldisk or Adapter. Each object within the collection has a Properties collection. The difference between the collection interface and the Enumerator collection interface is that the Enumerator class allows you to access objects within the collection as if it were a database result set, in that it holds a pointer to the previous and next objects available. When you use the standard collection, you would normally loop through with a For Each loop, but you have no direct bookmark into the collection, so accessing it initially and then accessing it later will not hold your place. Using the Enumerator rectifies this.

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