Subclass (hook) external programs

[moeur]

This is the .NET version of the hooking code I wrote for the VB6 Codebank.
http://www.vbforums.com/showthread.php?t=322261

This code allows you to hook into (subclass) external programs to intercept their windows messages. This allows you to do things like monitor button presses and keyboard input as well as respond to new menu items you can add to other programs which you don't have the source code for.

There are two parts to the code: a VB class and a C++ dll. I've attached the class and the compiled dll, the C++ dll source is in the previous thread if you want it.

Here is a description of the class clsHook.vb

Methods

GetWindowHandle(Caption, ClassName) - returns a handle to a top-level window
GetChildHandle(Caption, ClassName, TopLevelHandle) - returns a handle to a child window
AddMessage(NewMessage, strMessage) - Adds a windows message to the list of messages we want to monitor
SetHook - Sets the hook into the external program.
RemoveHook - Removes the hook from the external program.

Properties

isHooked - Returns True if the hook is set.
TargethWnd - Sets or returns the handle of the target window that is to be hooked

Events

SentMessage(ByRef m As Message) - Sent messages arrive here
SentRETMessage(ByRef m As Message) - Sent messages after processing arrive here
PostedMessage(ByRef m As Message) - Posted messages arrive here
HookError(Number, LocalMsg, APIMsg) - Raised on certain non-fatal error conditions
UnHook() - Raised when the hook is removed

Example

Public Class Form1
    'This Program hooks Notepad.exe and monitors WM_CHAR, 
    ' WM_LBUTTONDOWN, WM_LBUTTONUP messages
    Private WithEvents EditHook As New clsHook
    Private Const WM_LBUTTONDOWN = &H201
    Private Const WM_LBUTTONUP = &H202
    Private Const WM_CHAR = &H102

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
        Handles Button1.Click
        'Set the hook
        Dim hWndMain As Integer
        Dim hwndEdit As Integer
        'Get handle to notepad
        hWndMain = EditHook.GetWindowHandle(vbNullString, "NotePad")
        'Get handle to notepad's Edit window
        hwndEdit = EditHook.GetChildHandle("", "Edit", hWndMain)
        'Make that our target
        EditHook.TargethWnd = hwndEdit

        'Add the message(s) we want to look for
        EditHook.AddMessage(WM_CHAR, "WM_CHAR")
        EditHook.AddMessage(WM_LBUTTONDOWN, "WM_LBUTTONDOWN")
        EditHook.AddMessage(WM_LBUTTONUP, "WM_LBUTTONUP")
        'Set the hook
        EditHook.SetHook()
    End Sub

    Private Sub EditHook_PostedMessage(ByRef m As System.Windows.Forms.Message) _
        Handles EditHook.PostedMessage
        'Here is where Posted messages will arrive
        Dim myPoint As Int32
        Select Case m.Msg
            Case WM_CHAR
                'wParam points to char code
                TextBox1.Text &= EditHook.Messages(m.Msg) & ":  " & Chr(CByte(m.WParam.ToInt32)) _
                    & vbCrLf
            Case WM_LBUTTONUP, WM_LBUTTONDOWN
                'lParam: x-lo word, y-hi word
                myPoint = m.LParam.ToInt32
                TextBox1.Text &= EditHook.Messages(m.Msg) & ":  " & CStr(myPoint And &HFFFF) _
                    & " : " &                   CStr(myPoint \ &H10000) & vbCrLf   
             End Select
    End Sub
End Class

Edit: Added source code for C++ dll