HOWTO: Call CLSID And ProgID Related COM APIs in Visual Basic

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 5.0
• Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 32-bit only, for Windows, version 4.0

SUMMARY

This article demonstrates how to use a set of related Component Object Model (COM) APIs that retrieve and manipulate CLSIDs and ProgIDs. The following APIs are discussed:

• CLSIDFromProgID: To retrieve the CLSID of a COM object with a given ProgID.



• StringFromCLSID: To convert a CLSID structure to a string.



• CLSIDFromString: To convert a CLSID in string format to a structure.



• ProgIDFromCLSID: To retrieve a ProgID with a given CLSID.

MORE INFORMATION

WARNING: One or more of the following functions are discussed in this article; VarPtr, VarPtrArray, VarPtrStringArray, StrPtr, ObjPtr. These functions are not supported by Microsoft Technical Support. They are not documented in the Visual Basic documentation and are provided in this Knowledge Base article "as is." Microsoft does not guarantee that they will be available in future releases of Visual Basic.

1. Create a new ActiveX DLL project (Project1) in Visual Basic (Class1 is created by default).



2. Compile the default project. Now, you have a test component: Project1.dll, which contains a COM class (Project1.Class1)



3. Create a new Standard EXE project (Project1) in Visual Basic. Form1 is created by default.



4. Add three TextBoxes, one Command button, and one ListBox to Form1.



5. Add the following code to Form1's code module:




      ' ========== CODE FOR FORM1 ==============
      Option Explicit

      'CLSID/GUID structure
      '====================

      Private Type GUID
          Data1 As Long
          Data2 As Integer
          Data3 As Integer
          Data4(7) As Byte
      End Type

      'API Declarations:
      '=================

      Private Declare Function CLSIDFromProgID _
         Lib "ole32.dll" (ByVal lpszProgID As Long, _
         pCLSID As GUID) As Long

      Private Declare Function ProgIDFromCLSID _
         Lib "ole32.dll" (pCLSID As GUID, lpszProgID As Long) As Long

      Private Declare Function StringFromCLSID _
         Lib "ole32.dll" (pCLSID As GUID, lpszProgID As Long) As Long

      Private Declare Function CLSIDFromString _
         Lib "ole32.dll" (ByVal lpszProgID As Long, _
         pCLSID As GUID) As Long

      Private Declare Sub CopyMemory Lib "kernel32" Alias _
         "RtlMoveMemory" (pDst As Any, pSrc As Any, ByVal ByteLen As Long)

      Private Sub Command1_Click()
         Dim strProgID As String * 255
         Dim pProgID As Long
         Dim udtCLSID As GUID
         Dim strCLSID As String * 255
         Dim pCLSID As Long
         Dim lngRet As Long
         Dim strTemp As String
         Dim i As Integer

         'Take a ProgID.
         strTemp = Text1.Text

         'Get CLSID.
         lngRet = CLSIDFromProgID(StrPtr(strTemp), udtCLSID)

         'Display CLSID elements.
         With List1
            .AddItem Hex(udtCLSID.Data1)
            .AddItem Hex(udtCLSID.Data2)
            .AddItem Hex(udtCLSID.Data3)
            For i = 0 To 7
               .AddItem Hex(udtCLSID.Data4(i))
            Next
         End With

         'Convert CLSID to a string and get the pointer back.
         lngRet = StringFromCLSID(udtCLSID, pCLSID)

         'Get the CLSID string and display it.
         StringFromPointer pCLSID, strCLSID
         Text2.Text = strCLSID

         'Reinitialize the CLSID.
         With udtCLSID
            .Data1 = 0
            .Data2 = 0
            .Data3 = 0
            For i = 0 To 7
               .Data4(i) = 0
            Next
         End With

         'Convert the string back to CLSID.
         strTemp = Text2.Text
         lngRet = CLSIDFromString(StrPtr(strTemp), udtCLSID)

         'Get a pointer to ProgID string. This is a Unicode string.
         lngRet = ProgIDFromCLSID(udtCLSID, pProgID)

         'Get the ProgID and display it.
         StringFromPointer pProgID, strProgID
         Text3.Text = strProgID

      End Sub

      'This function takes a pointer to a Unicode string, a string buffer
      'and place the bytes in the Visual Basic string buffer.

      Private Sub StringFromPointer(pOLESTR As Long, strOut As String)
         Dim ByteArray(255) As Byte
         Dim intTemp As Integer
         Dim intCount As Integer
         Dim i As Integer

         intTemp = 1

         'Walk the string and retrieve the first byte of each WORD.
         While intTemp <> 0
            CopyMemory intTemp, ByVal pOLESTR + i, 2
            ByteArray(intCount) = intTemp
            intCount = intCount + 1
            i = i + 2
         Wend

         'Copy the byte array to our string.
         CopyMemory ByVal strOut, ByteArray(0), intCount
      End Sub

      Private Sub Form_Load()
         Text1.Text = "Project1.Class1"
      End Sub 

6. Run the project, and press Command1. The following appears:

Text1: Displays the ProgID of the component that you want to get the CLSID from.
Text2: Displays the CLSID retrieved in string format.
Test3: Displays the ProgID retrieved based on the CLSID.
List1: Displays the members of the CLSID structure in hex format.

Additional query words:

Keywords : kbGrpVB VBKBAX_VBKBComp
Version : WINDOWS:4.0,5.0
Platform : WINDOWS
Issue type : kbhowto