[Registry/Windows] Performing simple file associations

[bergerkiller]

These two functions allow you to associate a program with a certain file type:

Imports:

Imports System.Runtime.InteropServices

Main code:

<DllImport("shell32.dll", CharSet:=CharSet.Auto, SetLastError:=True)> _
    Private Shared Sub SHChangeNotify(ByVal wEventId As UInt32, ByVal uFlags As UInt32, ByVal dwItem1 As IntPtr, ByVal dwItem2 As IntPtr)
    End Sub
    Private Const SHCNE_ASSOCCHANGED As UInt32 = &H8000000
    Private Const SHCNF_IDLIST As UInt32 = &H0
 
    Public Shared Function Associate(ByVal type As String, ByVal typename As String, ByVal executable As String, Optional ByVal arguments As String = "%1") As Boolean
        DeAssociate(type)
        Try
            My.Computer.Registry.ClassesRoot.CreateSubKey("." & type).SetValue("", typename)
            My.Computer.Registry.ClassesRoot.CreateSubKey(typename & "\shell\open\command").SetValue("", executable & " " & arguments)
            My.Computer.Registry.ClassesRoot.CreateSubKey(typename & "\DefaultIcon").SetValue("", executable)
            SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, IntPtr.Zero, IntPtr.Zero)
            Return True
        Catch
            Return False
        End Try
    End Function
    Public Shared Function DeAssociate(ByVal type As String) As Boolean
        Try
            Dim typename As String = My.Computer.Registry.ClassesRoot.OpenSubKey("." & type).GetValue("")
            My.Computer.Registry.ClassesRoot.DeleteSubKey("." & type)
            My.Computer.Registry.ClassesRoot.DeleteSubKeyTree(typename)
            SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, IntPtr.Zero, IntPtr.Zero)
            Return True
        Catch
            Return False
        End Try
    End Function
    Public Shared Function IsAssociated(ByVal type As String) As Boolean
        Try
            Dim typename As String = My.Computer.Registry.ClassesRoot.OpenSubKey("." & type, False).GetValue("")
            My.Computer.Registry.ClassesRoot.OpenSubKey(typename, False)
            Return True
        Catch
            Return False
        End Try
    End Function

To associate:

Associate("type", "Type file", "C:\program files\typeopener.exe", "-i %1"

Associates the file type ".type" to the typeopener.exe program. When opening the file in Windows it will use the "-i %1" arguments, where "%1" is the file opened. The type displayed in the properties dialog will be "Type file".

To de-associate:

DeAssociate("type")

It will search the type name of "type" (="Type file") and removes both keys and for the type name the entire tree.

To check if a type is associated:

If IsAssociated("type") Then
     MessageBox.Show("Type is associated")
End If

Note that all these functions are not very solid, since they use a Try-Catch block to check if the operation is possible.
You could add checks to existing keys, but looping the GetSubKeyNames function could mean a loss of performance.
SHChangeNotify is used to make Windows update the association internally. (Icons)

For a more advanced class you could use FileAssociation.vb from Mentalis.org.

Special thanks go to Edgemeal.