PreFilterMessage + WM_ACTIVATE ??

[Rickard]

Does IMessageFilter.PreFilterMessage not work with all messages?
Consider the VB app at the bottom of this posting.

The WM_ACTIVATE in the overrided WndProc gets printed, but not the one
in the message filter (the message filter works for other messages like
WM_MOUSEDOWN). Is this behavior by design? There is not mention of which
messaged gets filtered in the documentation for IMessageFilter.
Is there some way to catch WM_ACTIVATE for all windows in my app without
overriding all WndProcs?

------------------------------------------------------------------
Public Class Form1
Implements IMessageFilter


Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click

Dim f As New Form2
f.Show()
End Sub

Public Function PreFilterMessage( _
ByRef m As System.Windows.Forms.Message) As Boolean _
Implements System.Windows.Forms.IMessageFilter.PreFilterMessage

Static i As Integer = 0
If m.Msg = 6 Then
i += 1
Debug.Print("Activate " & i)
End If
End Function

Private Sub Button2_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button2.Click

Application.AddMessageFilter(Me)
End Sub

Protected Overrides Sub WndProc( _
ByRef m As System.Windows.Forms.Message)

Static i As Integer = 0
If m.Msg = 6 Then
i += 1
Debug.Print("WM_ACTIVATE " & i)
End If
MyBase.WndProc(m)

End Sub
End Class
------------------------------------------------------------------

 

[Rickard]

I wrote a simple app that logged all messages. Here is the result. It
seems there is quite a lot of messages not handled by PreFilterMessage.


(0x00ae): WndProc, NOT PreFilterMessage
(0x0118): PreFilterMessage, NOT WndProc
(0xc136): WndProc, NOT PreFilterMessage
WM_ACTIVATE: WndProc, NOT PreFilterMessage
WM_ACTIVATEAPP: WndProc, NOT PreFilterMessage
WM_CAPTURECHANGED: WndProc, NOT PreFilterMessage
WM_CHANGEUISTATE: WndProc, NOT PreFilterMessage
WM_CREATE: WndProc, NOT PreFilterMessage
WM_CTLCOLORBTN: WndProc, NOT PreFilterMessage
WM_CTLCOLORLISTBOX: WndProc, NOT PreFilterMessage
WM_DRAWITEM: WndProc, NOT PreFilterMessage
WM_ENTERSIZEMOVE: WndProc, NOT PreFilterMessage
WM_ERASEBKGND: WndProc, NOT PreFilterMessage
WM_EXITSIZEMOVE: WndProc, NOT PreFilterMessage
WM_GETICON: WndProc, NOT PreFilterMessage
WM_GETMINMAXINFO: WndProc, NOT PreFilterMessage
WM_GETTEXT: WndProc, NOT PreFilterMessage
WM_GETTEXTLENGTH: WndProc, NOT PreFilterMessage
WM_MOUSEACTIVATE: WndProc, NOT PreFilterMessage
WM_MOVE: WndProc, NOT PreFilterMessage
WM_NCACTIVATE: WndProc, NOT PreFilterMessage
WM_NCCALCSIZE: WndProc, NOT PreFilterMessage
WM_NCCREATE: WndProc, NOT PreFilterMessage
WM_NCHITTEST: WndProc, NOT PreFilterMessage
WM_NCPAINT: WndProc, NOT PreFilterMessage
WM_NOTIFYFORMAT: WndProc, NOT PreFilterMessage
WM_PARENTNOTIFY: WndProc, NOT PreFilterMessage
WM_PRINTCLIENT: WndProc, NOT PreFilterMessage
WM_QUERYUISTATE: WndProc, NOT PreFilterMessage
WM_SETCURSOR: WndProc, NOT PreFilterMessage
WM_SETICON: WndProc, NOT PreFilterMessage
WM_SETTEXT: WndProc, NOT PreFilterMessage
WM_SHOWWINDOW: WndProc, NOT PreFilterMessage
WM_SIZE: WndProc, NOT PreFilterMessage
WM_SIZING: WndProc, NOT PreFilterMessage
WM_STYLECHANGED: WndProc, NOT PreFilterMessage
WM_STYLECHANGING: WndProc, NOT PreFilterMessage
WM_SYNCPAINT: WndProc, NOT PreFilterMessage
WM_SYSCOMMAND: WndProc, NOT PreFilterMessage
WM_UPDATEUISTATE: WndProc, NOT PreFilterMessage
WM_WINDOWPOSCHANGED: WndProc, NOT PreFilterMessage
WM_WINDOWPOSCHANGING: WndProc, NOT PreFilterMessage

 

[Claes Bergefall]

PreFilterMessage will only notify you of messages that are posted to the
message queue (after they are pulled from it but before they are
dispatched). WM_ACTIVATE is sent directly to the window procedure, not
posted in the message queue. Most (but not all) of the mouse messages are
posted to the queue.

The keywords here are "posted" and "sent" (see PostMessage and SendMessage
resp.). Only posted messages will show up in your PreFilterMessage routine

/claes

 

[Stoitcho Goutsev \(100\)]

Rickard,

PreFilterMessage filters messages that comes through the application message
queue in other words they are posted rather than sent. There are not a lot
of messages like this. Besically these are messages from the mouse, keyboard
and few others.
On the other hand the WndProc is the target for all messages, so you are
going to receive them all there.

You can use the Spy++ tool to spy on all messages send or posted to an
application. For all messages in the log there there is a mark if the
message has been sent or posted. If I remember correctly posted messages are
marked with P and sent send with S. Only messages marked with P can be
filtered in PreFilterMessage.