Question

Sorry if there is already made such question earlier, but I have no time at the moment to dig in stackoverflow db …

So, I have this code:

procedure TForm1.GraphPrevBtnMouseEnter(Sender: TObject);
var frm_PrevBtn : TForm;
begin
  GraphPrevBtn.Width := 75;
  if z = 0 then begin
    frm_PrevBtn := TForm.Create(nil);
    with frm_PrevBtn do begin
      Name := 'frm_PrevBtn';
      BorderStyle := bsNone;
      Position := poDesigned;
      Top := Form1.Top + GraphprevBtn.Top + (form1.Height - Form1.ClientHeight) - 3;
      Left := Form1.Left + GraphprevBtn.Left + 3;
      Width := GraphprevBtn.Width; Height := GraphprevBtn.Height; transparentColor := True; TransparentColorValue := clbtnFace;
      Show;
    end;
    GraphPrevBtn.Parent := frm_PrevBtn;
    if GetLastError = 0 then z := frm_prevBtn.GetHashCode;
  end;
end;

procedure TForm1.GraphPrevBtnMouseLeave(Sender: TObject);
    var frm_PrevBtn_H : THandle;
    begin
    // if form is created then- if mouse is under button then- if z = formshashcode ( form is on creatin stage )
      if not (FindVCLWindow(Mouse.CursorPos) = GraphPrevBtn) and ((FindControl(FindWindow('TForm','frm_PrevBtn')) as TForm).Visible = True) and (GraphPrevBtn.Parent = FindControl(FindWindow('TForm','frm_PrevBtn')) as TForm) then begin // if mouse is not under graphprevBtn
        ShowMessage(FindVCLWindow(Mouse.CursorPos).Name); // 
        if z = 112                                                       // then if form is created
        then begin
            GraphPrevBtn.Parent := Form1;
            GraphPrevBtn.bringtoFront;
            GraphPrevBtn.Top := 29; GraphPrevBtn.Left := 226;
            (FindControl(FindWindow('TForm','frm_PrevBtn')) as TForm).Free;
            if GetLastError = 0 then z := 0;
          end;
      end;
   end;

So, my wish is the following:
When I enter this GraphPrevBtn with mouse, form is created. As for is created, the focus goes from Control to new form. As focus is to new form, the OnMouseLeave event is fired. As event is fired, it should destroy the form, BUT ONLY IF user ( NOT active control / focus ) actually leaves control by mouse.

What happens now is that either new forms is not destroyed at all or both events goes infinite loop ( *frm_PrevBtn* is created and destroyed again and again and again…).

What would be best solution?

My idea is to get new forms rect and check whenever mouse is inside this rect. If it is, then perform allow OnMouseLeave event, otherwise deattach it … would it work?

As much I tried with these samples:

1. http://delphi.about.com/od/windowsshellapi/a/get-active-ctrl.htm

2. http://delphi.about.com/od/delphitips2010/qt/is-some-delphi-tcontrol-under-the-mouse.htm

   • No luck. Where is the problem … ?

Remarks: global var z : byte;

P.S. Thanks for negative votes … great motivation to use this site in future …

Answer 1

Mouse enters on ‘GraphPrevBtn’, you create a form over the button. As soon as this form becomes visible, since mouse is not anymore over ‘GraphPrevBtn’, ‘OnMouseLeave’ is fired. You destroy the new form and now mouse is again on the button so ‘OnMouseEnter’ is fired, hence the infinite loop.

As a solution, you can move the form disposing code to ‘OnMouseEnter’ of Form1:

procedure TForm1.FormMouseEnter(Sender: TObject);
begin
  if z = 112
  then begin
    GraphPrevBtn.Parent := Form1;
    [...]

.. and what’s with the ‘GetLastError’, it seems fully irrelevant. If you’re going to use it, at least set last error to ‘0’ by calling GetLastError or SetLastErrorbefore beginning your operation.