problem with api-call

[escape0]

hi... i've a problem with an api-call

the class should prevent the ExtCombobox from opening the dropdown-box.

Public Class ExtComboBox
    Inherits ComboBox

    Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
    Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
    Private Declare Function GetWindowRect Lib "user32" Alias "GetWindowRect" (ByVal hwnd As Long, ByVal lpRect As RECT) As Long
    Private Declare Function ShowWindow Lib "user32" Alias "ShowWindow" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long

    Private Structure rect
        Dim Left As Long
        Dim Top As Long
        Dim Right As Long
        Dim Botton As Long
    End Structure

    Private Const GWL_WNDPROC = (-4)
    Private Const WM_CTLCOLORLISTBOX = &H134

    Private lbRect As rect
    Private hWndLB As Long

    Private OldWndPrg As Long

    ' Subclassing einschalten
    Public Sub ChangeWndPrg(ByVal hwnd As Long)
        OldWndPrg = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf WndPrg)
    End Sub

    ' Subclassing ausschalten
    Public Sub ResetWndPrg(ByVal hwnd As Long)
        SetWindowLong(hwnd, GWL_WNDPROC, OldWndPrg)
    End Sub

    Public Function WndPrg(ByVal hwnd As Long, _
                           ByVal uMsg As Long, _
                           ByVal wParam As Long, _
                           ByVal lParam As Long) As Long

        If uMsg = WM_CTLCOLORLISTBOX Then

            ' lParam = Handler für Listbox-Window
            hWndLB = lParam

            ' Ausmasse des Windows ermitteln, das erzeugt wird
            GetWindowRect(hWndLB, lbRect)

            ' Wir verhindern damit, dass die Listbox aufgeklappt wird
            ' Parameter: SW_Hidde = 0&
            ShowWindow(hWndLB, 0&)
        End If

        ' Alle Nachrichten an die Fensterprozedur weiterleiten
        Return CallWindowProc(OldWndPrg, hwnd, uMsg, wParam, lParam)
    End Function

End Class

The compiler doesn't accept this code because in ChangeWndPrg the AdressOf-instruction doesn't return a long value.

has andybody an idea how to solve this problem?

thanks
robert

[Pirate]

Change the long to interger and see if that's the problem !

[jovton]

You must add a delegate for the AddressOf operator, and change the parameter of the function declaration to the Delegate type.

See the following topic in the online MSDN Library:

http://msdn.microsoft.com/library/en...l/vbup1048.asp

[jovton]

I have a problem with the API call GetWindowLong in regard to the AddressOf operator though.

Does anyone know how to use the GetWindowLong API call in VB.NET using the GWL_WNDPROC constant as the last parameter, and then use the return value to point to a delegate using the AddressOf operator? Yes it's probably easier said than done. But take a look at this scenario:

I have a class named CFoo, okay. It has a Public variable named lpPrevWndFunc, another called frm of type Windows.Forms.Form, and another variable called hwnd of type Long.

I have an instance of the CFoo class called Foo. Okay, now... in a public module SubClass.vb:

Module modSubclass
 
   Delegate Function SubClassProcDelegate(ByVal hwnd As Integer, _
                                          ByVal msg As Integer, _
                                          ByVal wParam As Integer, _
                                          ByVal lParam As Integer) As Integer
 
   Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" _
                            (ByVal lpPrevWndFunc As Integer, _
                             ByVal hwnd As Integer, _
                             ByVal msgWinMessage As Integer, _
                             ByVal wParam As Integer, _
                             ByRef lParam As Integer) As Integer
 
   Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" 
                            (ByVal hwnd As Integer, _
                             ByVal nIndex As Integer, _
                             ByVal dwNewLong As SubClassProcDelegate) As Integer
 
   Private Function SubclassWndProc(ByVal hwnd As Integer, _
                                      ByVal msgWinMessage As Integer, _
                                      ByVal wParam As Integer, _
                                      ByVal lParam As Integer) As Integer
 
   
       ' code hidden ;oP
     
   End Function
 
 
   Public Sub DoSubclass(ByRef frm As Windows.Forms.Form)
 
        Dim Foo As New CFoo
 
        ' Create the object as a form
        Foo.frm = frm
        Foo.hwnd = frm.Handle.ToInt32
        Foo.lpPrevWndFunc = GetWindowLong(frm.Handle.ToInt32, GWL_WNDPROC)
 
        ' Replace the basic window procedure of the
        ' form calling this procedure
 
        Call SetWindowLong(frm.Handle.ToInt32, _
                           GWL_WNDPROC, _
                           AddressOf SubclassWndProc)
 
   End Sub
 
   Public Sub UnSubClass(ByRef frm As Windows.Forms.Form)
 
        Dim hHelp As New HTMLHelp
 
        ' Release the subclassed form
 
        Call SetWindowLong(frm.Handle.ToInt32, _
                           GWL_WNDPROC, _
                           Foo.lpPrevWndFunc)
 
   End Sub
 
End Module

My real question is... of what type should the class member lpPrevWndFunc be in the class CFoo? Can it be of Type AppName.modSubClass.SubClassProcDelegate? Because if it can then the GetWindowLong returns a value of the wrong type. I would get the error:

Value of type 'Integer' cannot be converted to 'AppName.modSubclass.SubClassProcDelegate'.

Thanks to anyone who makes effort in helping me out.

[dynamic_sysop]

try this link for an article on codeproject...
Subclassing in VB.Net

[dynamic_sysop]

a simple example of subclassing controls , based on the above is this ....

[Color=Blue]Private[/COLOR] [Color=Blue]Const[/COLOR] WM_CTLCOLORLISTBOX [Color=Blue]As[/COLOR] [Color=Blue]Integer[/COLOR] = [Color=Blue]CInt[/COLOR](&H134)
 
    [Color=Blue]Private[/COLOR] [Color=Blue]Declare[/COLOR] [Color=Blue]Function[/COLOR] ShowWindow [Color=Blue]Lib[/COLOR] "user32.dll" ([Color=Blue]ByVal[/COLOR] hwnd [Color=Blue]As[/COLOR] [Color=Blue]Integer[/COLOR], [Color=Blue]ByVal[/COLOR] nCmdShow [Color=Blue]As[/COLOR] [Color=Blue]Integer[/COLOR]) [Color=Blue]As[/COLOR] [Color=Blue]Integer
 
[/COLOR]    [Color=Blue]Private[/COLOR] [Color=Blue]WithEvents[/COLOR] sbclss [Color=Blue]As[/COLOR] SubClass
 
    [Color=Blue]Private[/COLOR] [Color=Blue]Sub[/COLOR] Button1_Click([Color=Blue]ByVal[/COLOR] sender [Color=Blue]As[/COLOR] System.Object, [Color=Blue]ByVal[/COLOR] e [Color=Blue]As[/COLOR] System.EventArgs) [Color=Blue]Handles[/COLOR] Button1.Click
        sbclss = [Color=Blue]New[/COLOR] SubClass(ComboBox1.Handle)
        sbclss.IsSubClassed = [Color=Blue]True
[/COLOR]    [Color=Blue]End[/COLOR] [Color=Blue]Sub
 
[/COLOR]    [Color=Blue]Private[/COLOR] [Color=Blue]Sub[/COLOR] sbclss_Proc([Color=Blue]ByVal[/COLOR] m [Color=Blue]As[/COLOR] Message) [Color=Blue]Handles[/COLOR] sbclss.MyBaseProc
        [Color=Blue]If[/COLOR] m.Msg = WM_CTLCOLORLISTBOX [Color=Blue]Then
[/COLOR]            ShowWindow(m.HWnd.ToInt32, 0)
        [Color=Blue]End[/COLOR] [Color=Blue]If
[/COLOR]    [Color=Blue]End[/COLOR] [Color=Blue]Sub
End[/COLOR] [Color=Blue]Class
 
Public[/COLOR] [Color=Blue]Class[/COLOR] SubClass
    [Color=Blue]Inherits[/COLOR] System.Windows.Forms.NativeWindow
    [Color=Blue]Public[/COLOR] [Color=Blue]Event[/COLOR] MyBaseProc([Color=Blue]ByVal[/COLOR] m [Color=Blue]As[/COLOR] Message)
 
    [Color=Blue]Public[/COLOR] IsSubClassed [Color=Blue]As[/COLOR] [Color=Blue]Boolean[/COLOR] = [Color=Blue]False
[/COLOR]    [Color=Blue]Sub[/COLOR] [Color=Blue]New[/COLOR]([Color=Blue]ByVal[/COLOR] Handle [Color=Blue]As[/COLOR] IntPtr)
        [Color=blue]MyBase[/color].AssignHandle(Handle)
    [Color=Blue]End[/COLOR] [Color=Blue]Sub
 
[/COLOR]    [Color=Blue]Protected[/COLOR] [Color=Blue]Overrides[/COLOR] [Color=Blue]Sub[/COLOR] WndProc([Color=Blue]ByRef[/COLOR] m [Color=Blue]As[/COLOR] System.Windows.Forms.Message)
        [Color=Blue]If[/COLOR] IsSubClassed [Color=Blue]Then
[/COLOR]            [Color=Blue]RaiseEvent[/COLOR] MyBaseProc(m)
        [Color=Blue]End[/COLOR] [Color=Blue]If
[/COLOR]        [Color=blue]MyBase[/color].WndProc(m)
    [Color=Blue]End[/COLOR] [Color=Blue]Sub
End[/COLOR] [Color=Blue]Class[/COLOR]

[jovton]

Seeing that I'm in the early stages of the migration phase I would state that you my friend, are a lifesaver! Thanks.