CODEWITHSUNDEEP
delphiforms
hashiQ
hashiQ

Reputation: 1

Problem with set visible of form - after some time form generate exeption

I have problem with my form application created in Delphi 5. In this app I have few buttons which open (set visible property) different forms. This forms as a parent have Panel. Only one function is overridden:

procedure TForm.CreateParams(var Params : TCreateParams);
begin
  inherited CreateParams(Params);
  with Params do begin
    Style := ws_Child; 
    X :=FormMain.panelMain.Left; 
    Y :=FormMain.panelMain.Top;   
    Height :=FormMain.panelMain.Height; 
    Width := FormMain.panelMain.Height; 
    WndParent := FormMain.Handle;
  end
end;

I have also function to change actual form on panel:


procedure TFormMain.ChangeToForm(newForm: TMainForm);
begin

  if (newForm=nil) or (newForm=lastForm) then EXIT;
  actForm:=newForm;

  actForm.Visible :=true;
  if assigned(lastForm) then lastForm.Visible:=false;
  lastForm:=actForm;
  LabelScreen.Caption:=actForm.Caption;
  newForm.Left := 0;
  newForm.Top := 0;

  newForm.Width := panelMDI.Width;
  newForm.Height := panelMDI.Height;
  newForm.Left := panelMDI.Left;
  newForm.Top := panelMDI.Top;
end;

When I open application everything works fine. Buttons change forms. Everything is ok. But when user don't use this app (don't changes forms etc.) for some period of time. Clicking on the buttons generate exceptions:



Access violation at address 0044D761 in module 'rozpoznawanie.exe'. Read of address 00000004; EAccessViolation

[...]
00534f2e       jz      loc_534fe9
00534f34 196   mov     eax, [ebp-8]
00534f37       mov     [$54b3a4], eax
00534f3c 197   mov     dl, 1
00534f3e       mov     eax, [$54b3a4]
00534f43     > call    -$9c194 ($498db4)      ; Forms.TCustomForm.SetVisible
00534f48 198   cmp     dword ptr [$54b3a8], 0
00534f4f       jz      loc_534f5d
00534f51       xor     edx, edx
00534f53       mov     eax, [$54b3a8]
00534f58       call    -$9c1a9 ($498db4)      ; Forms.TCustomForm.SetVisible
[...]

I've looked everywhere and I don't know why it appears. Do you have some ideas?

EDIT

I found that the problem may be earlier:



00756bc8 vcl70.bpl Controls.TWinControl.HandleNeeded 
00756bd5 vcl70.bpl Controls.TWinControl.GetHandle 
0076e675 vcl70.bpl Forms.TCustomForm.GetMonitor 
0076ecd0 vcl70.bpl Forms.TCustomForm.SetWindowToMonitor 
0076daf1 vcl70.bpl Forms.TCustomForm.SetVisible

in SetWindowToMonitor I read that if on computer we have installed more than one monitor sometimes this problem appears. But I tried change DefaultMonitor property and this is not working.

Upvotes: 0

Views: 2283

Answers (2)

Toon Krijthe
Toon Krijthe

Reputation: 53436

In addition, is:

Height :=FormMain.panelMain.Height; 
Width := FormMain.panelMain.Height;

A typo? Else use

Height :=FormMain.panelMain.Height; 
Width := FormMain.panelMain.Width;

Upvotes: 0

hashiQ
hashiQ

Reputation: 1

I probably found solution for my problem. I have Delphi 5 without Update Pack 1. I do some research and I found that the problem as I said is in Delphi function TCustomForm.GetMonitor On production computer is installed one real monitor and virtual (Radmin application). After installing UP1 problem disapears.
I could also change function by myself:


function TCustomForm.GetMonitor: TMonitor;
var
  HM: HMonitor;
  I: Integer;
begin
  Result := nil;
  HM := MonitorFromWindow(Handle, MONITOR_DEFAULTTONEAREST);
  for I := 0 to Screen.MonitorCount - 1 do
    if Screen.Monitors[I].Handle = HM then
    begin
      Result := Screen.Monitors[I];
      Exit;
    end;

  //if we get here, the Monitors array has changed, so we need to clear and reinitialize it
  for i := 0 to Screen.MonitorCount-1 do
    TMonitor(Screen.FMonitors[i]).Free;
  Screen.FMonitors.Clear;
  EnumDisplayMonitors(0, nil, @EnumMonitorsProc, LongInt(Screen.FMonitors));
  for I := 0 to Screen.MonitorCount - 1 do
    if Screen.Monitors[I].Handle = HM then
    begin
      Result := Screen.Monitors[I];
      Exit;
    end;    
end;

Thanks for any comments !

Upvotes: 0

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