Drydo's Blog

To be quite frank, after 3 months of ASP.NET development, the opportunity to do some down and dirty API programming really appealled to me today. So, the question (as indicated by the title) involved a member wanting to disable the right-click context menu from the Flash ActiveX component when being used in a WinForms application. (See previous blog entries for examples of Flash in VB.NET and communication between the two such as http://blogs.vbcity.com/drydo/archive/2005/10/18/5586.aspx).

The simple answer is to capture the right-click of the Flash Window itself and prevent it from being processed. A little play with Spy++ quickly came up with the answers and the rest was all about good old fashioned subclassing. I must admit it pinched the API declarations from Pinvoke.net and smartened them up a tad and that is pretty much it.

For the record, this is something I've been meaning to do for a while + I can leave work not feeling like some CSS floozy :)

Note: to recreate, create one form, one button and add one Flash Active X control. Copy and Paste as necessary. Tested in VS2005. If you get the dreaded 'Failed to import the ActiveX control' message, check out this workaround

Imports System.Runtime.InteropServices

Public Class Form1

#Region "API Routines"

    <DllImport("User32.dll")> _
   Private Shared Function EnumChildWindows _
       (ByVal WindowHandle As IntPtr, ByVal Callback As EnumWindowProcess, _
       ByVal lParam As IntPtr) As Boolean
    End Function

    <DllImport("user32.dll", CharSet:=CharSet.Auto)> _
Private Shared Sub GetClassName(ByVal hWnd As System.IntPtr, _
   ByVal lpClassName As System.Text.StringBuilder, ByVal nMaxCount As Integer)
    End Sub

    <DllImport("user32.dll", CharSet:=CharSet.Auto)> _
    Private Overloads Shared Function SetWindowLong(ByVal hWnd As IntPtr, ByVal
 nIndex As Integer, ByVal dwNewLong As Integer) As Integer
    End Function

    <DllImport("user32.dll", CharSet:=CharSet.Auto)> _
    Private Overloads Shared Function SetWindowLong(ByVal hWnd As IntPtr, ByVal
 nIndex As Integer, ByVal dwNewLong As FlashCaptureRoutine) As Integer
    End Function

    <DllImport("user32.dll", CharSet:=CharSet.Auto)> _
     Private Shared Function CallWindowProc(ByVal lpPrevWndFunc As Integer, ByVal
 hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer
    End Function

#End Region

#Region "Delegates"

    ' Used for processing Flash Window messages
    Public Delegate Function FlashCaptureRoutine(ByVal hwnd As Integer, ByVal
 Msg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer

    ' Used for enumerating child windows
    Public Delegate Function EnumWindowProcess(ByVal Handle As IntPtr, ByVal Parameter As IntPtr) As Boolean

#End Region

    ' Constants
    Public Const GWL_WNDPROC As Integer = (-4)
    Public Const WM_ENTERMENULOOP As Integer = &H211
    Public Const WM_RBUTTONDOWN As Integer = &H204
    Public Const WM_INITMENU = &H116

    ' Private vars
    Private mFlashWindowHandle As IntPtr
    Private mPreviousHandle As Integer
    Private isCapturing As Boolean

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal 
e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        ' Cleanup if appropriate
        If isCapturing Then CleanupCapture()
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal 
e As System.EventArgs) Handles MyBase.Load
        ' Load the test movie...
        Me.AxShockwaveFlash1.Movie = "MyTestMovie.swf"
        Me.AxShockwaveFlash1.Menu = True
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal 
e As System.EventArgs) Handles Button1.Click
        ' Capture / Reset Flash Window Processing as appropriate

        ' React as approrpiate
        If isCapturing Then
            ' Resume
            CleanupCapture()
        Else
            ' Capture events
            CaptureRightClick()
        End If
        ' Switch over the flag
        isCapturing = Not isCapturing
    End Sub

    Private Sub CaptureRightClick()
        ' Attempt to obtain the Flash Window
        EnumChildWindows(Me.Handle, 
AddressOf EnumWindow, IntPtr.Zero)
        ' Subclass using new routine storing the old result
        mPreviousHandle = SetWindowLong(mFlashWindowHandle, GWL_WNDPROC, AddressOf FlashWindowCapture)
    End Sub

    Private Sub CleanupCapture()
        ' Reset back to the original handle...
        SetWindowLong(mFlashWindowHandle, GWL_WNDPROC, mPreviousHandle)
    End Sub

    Private Function FlashWindowCapture(ByVal hwnd As Integer, ByVal Msg As Integer, 
ByVal wParam As Integer, ByVal lParam As Integer) As Integer

        ' Capture the appropriate message and prevent it from being processed
        Select Case Msg
            Case WM_RBUTTONDOWN
                ' Exit
                Exit Function            
        End Select

        ' Carry on...
        Return CallWindowProc(mPreviousHandle, hwnd, Msg, wParam, lParam)
    End Function

    Private Function EnumWindow(ByVal Handle As IntPtr, ByVal Parameter As IntPtr) As Boolean
        ' Obtain the class name of the child window
        Dim ClassName As New System.Text.StringBuilder("", 255)
        GetClassName(Handle, ClassName, ClassName.MaxCapacity)

        ' Is this the Flash Window?
        If ClassName.ToString = "MacromediaFlashPlayerActiveX" Then
            mFlashWindowHandle = Handle
        End If
        Return True
    End Function

End Class