Binaryworld - DeleteFileAssociation - Unregister a file extension ... [ VB -> Windows ]

Private Declare Sub SHChangeNotify Lib "shell32.dll" (ByVal wEventId As Long, _
  ByVal uFlags As Long, ByVal dwItem1 As Long, ByVal dwItem2 As Long)
Const SHCNE_ASSOCCHANGED = &H8000000
Const SHCNF_IDLIST = 0

' Destroy a file association
'
' NOTE: requires the GetRegistryValue and DeleteRegistryKey functions

Sub DeleteFileAssociation(ByVal Extension As String)
  Dim ClassName As String

  Const HKEY_CLASSES_ROOT = &H80000000

  ' ensure that there is a leading dot
  If Left(Extension, 1) <> "." Then
    Extension = "." & Extension
  End If
  ' read the associated class name
  ClassName = GetRegistryValue(HKEY_CLASSES_ROOT, Extension, "")
  ' exit if there is no extension association
  If Len(ClassName) = 0 Then Exit Sub

  ' delete this key
  DeleteRegistryKey HKEY_CLASSES_ROOT, Extension
  ' delete the other key where registration data is found
  DeleteRegistryKey HKEY_CLASSES_ROOT, ClassName

  ' notify Windows that file associations have changed
  SHChangeNotify SHCNE_ASSOCCHANGED, SHCNF_IDLIST, 0, 0
End Sub