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Frequently Asked Questions

Trapping messages in non client area of a form.

Question:

How can I trap messages in the non client areas of my form, such as the title bar?

Answer:

Create a message handler for one of the variety of WM_NC

(non client) messages available to trap. (search the Windows

API help file for WM_NC). This example shows how to track 

mouse movement in all of the non client areas of the form.



Example:



unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

  private

     procedure WMNCMOUSEMOVE(var Message: TMessage);

       message WM_NCMOUSEMOVE;

    { Private declarations }

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



procedure TForm1.WMNCMOUSEMOVE(var Message: TMessage);

var

  s : string;

begin

  case Message.wParam of

    HTERROR : s := 'HTERROR';

    HTTRANSPARENT : s := 'HTTRANSPARENT';

    HTNOWHERE : s := 'HTNOWHERE';

    HTCLIENT : s := 'HTCLIENT';

    HTCAPTION : s := 'HTCAPTION';

    HTSYSMENU : s := 'HTSYSMENU';

    HTSIZE : s := 'HTSIZE';

    HTMENU : s := 'HTMENU';

    HTHSCROLL : s := 'HTHSCROLL';

    HTVSCROLL : s := 'HTVSCROLL';

    HTMINBUTTON : s := 'HTMINBUTTON';

    HTMAXBUTTON : s := 'HTMAXBUTTON';

    HTLEFT : s := 'HTLEFT';

    HTRIGHT : s := 'HTRIGHT';

    HTTOP : s := 'HTTOP';

    HTTOPLEFT : s := 'HTTOPLEFT';

    HTTOPRIGHT : s := 'HTTOPRIGHT';

    HTBOTTOM : s := 'HTBOTTOM';

    HTBOTTOMLEFT : s := 'HTBOTTOMLEFT';

    HTBOTTOMRIGHT : s := 'HTBOTTOMRIGHT';

    HTBORDER : s := 'HTBORDER';

    HTOBJECT : s := 'HTOBJECT';

    HTCLOSE : s := 'HTCLOSE';

    HTHELP : s := 'HTHELP';

    else s := '';

 end;

 Form1.Caption := s;

 Message.Result := 0;

end;



end.

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