Christian, ...
No words can tell you how I feel! Many, many, many thanks! I will spend time tomorrow trying to reconstruct your answer and of course, if I managed to get it solved, I will post an new result-summary to the MI-list. Kind regards! Milo -----Oorspronkelijk bericht----- Van: Christian Singer [mailto:[EMAIL PROTECTED] Verzonden: woensdag 15 maart 2006 12:48 Aan: Milo van der Linden; [email protected] Onderwerp: RE: [MI-L] Callback in vb.net At 16:54 14.03.2006 +0100, Milo van der Linden wrote: >Hello Christian (list), > >You answered my previous question on callbacks, so I hope you don't >find it rude that I ask you one more. > >I have the callback up and running and manage to get the "click" event >in MapInfo into a msgbox. I am also able to show the statustext on the >statusbar. However, When I store the returnd X and Y coordinates from >the callback in a variable and call another form with it, my newly >opened form hangs. I have been searching myself a roundtrip in the >world of threading, invoke and marshalling, but I cannot get it >running. > >Any ideas of how I can make the callback function end up in the same >thread as my main application? > >Kind regards, > >Milo van der Linden Hello Milo, with callback functions it is generally advisable to return control to the caller (here the MapInfo COM/OLE object) immediately, i.e. without potential delays caused by user interaction requests etc. The creation of a new form from within the callback function should thus be avoided. Instead the callback function could store the received parameters in persistent variables, then trigger a user event with the "PostMessage" API function and then return control to the caller. The event can then be processed by the receiving window/form without blocking the OLE server's thread. The code sample given before requires the following extensions and modifications: At first you'll need some Win32 API InterOp declarations: Class Win32Api Public Const WM_USER As Int32 = &H400 Public Declare Auto Function PostMessage Lib "user32.dll" _ (ByVal hwnd As IntPtr, _ ByVal wMsg As Int32, ByVal wParam As Int32, _ ByRef lParam As IntPtr) As Int32 End Class The following class variables are persistent / "Shared" members of the main window class (could as well be in a general app class etc.): Public Shared sLastUserEventX As String Public Shared sLastUserEventY As String Public Shared hwndMain As IntPtr Within the constructor of the main window (form1.new()) the window handle is saved permanently for later access from outside the form's class: hwndMain = Me.Handle Then the window procedure of the main form is customized so as to react to the event triggered by the callback function and display a second form: Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message) If m.Msg = Win32Api.WM_USER Then Dim myForm2 As New Form2() myForm2.Show() Else MyBase.WndProc(m) End If End Sub The callback function parses the received string parameter and saves the coordinate values into the public variables of the main window's class, then triggers the WM_USER event and returns without delay: Public Sub SelectGeneric(ByVal str As String) Dim split As String() = str.Split(",") Form1.sLastUserEventX = split(0).Substring(3) Form1.sLastUserEventY = split(1) Win32Api.PostMessage(Form1.hwndMain, Win32Api.WM_USER, 0, 0) End Sub The second form, intended to display the coordinate values, fetches these values from the respective variables in the contstructor (new()) function and puts these into two text boxes: TextBox1.Text = Form1.sLastUserEventX TextBox2.Text = Form1.sLastUserEventY Does this solve your problem? Regards, Christian Singer Ing.-Büro Christian Singer Singerhoffstr. 14 44225 Dortmund Germany E-mail: [EMAIL PROTECTED] WWW : www.icsinger.de Phone : +49 231 791464 Fax : +49 231 791460 _______________________________________________ MapInfo-L mailing list [email protected] http://www.directionsmag.com/mailman/listinfo/mapinfo-l
