How to restore a minimized modal form?

Question

I have a Form that is shown modal from the MainForm. In this modal form I override the WM_SYSCOMMAND like this :

protected
  procedure WMSysCommand(var Msg: TWMSysCommand);  message WM_SYSCOMMAND;

procedure TModalDlg.WMSysCommand(var Msg: TWMSysCommand);
begin
 if (fsModal in FormState) and (Msg.CmdType and $FFF0 = SC_MINIMIZE)
  then Application.MainForm.WindowState:= wsMinimized
  else inherited;
end;

... and when I minimize the modal form, the whole application is minimized. Everything is ok, but when I click on the taskbar button and the application is restored, the foscused window is the MainForm, not the modal one, like it should. What should I do to restore the app with the most modal form focused ?

Answer 1

In your current design you have a taskbar button for a minimized window which is disabled because of the modal form. I don't think you will be able to work out a sensible solution for this setup, neither form receives a WM_SYSCOMMAND - modal form because it doesn't have a taskbar button and the main form because it is disabled.

Change your strategy and switch taskbar buttons when you are minimizing the modal form. That is, you'll have a taskbar button for the modal form and not for the main form. You can then intercept and reverse in the same event handler when you receive a restore command. Below is a working example, but I should note that changing the window owner of a window after it has been created is strongly discouraged and in fact not documented any more for quite some time.

type
  TModalDlg = class(TForm)
    ...
  private
    FParentWnd: HWND;
  protected
    procedure WMSysCommand(var Msg: TWMSysCommand); message WM_SYSCOMMAND;
  end;

...

procedure TModalDlg.WMSysCommand(var Msg: TWMSysCommand);
begin
  if (fsModal in FormState) then begin
    case Msg.CmdType and $FFF0 of
      SC_MINIMIZE:
        begin
          SetWindowLong(Handle, GWL_EXSTYLE,
              (GetWindowLong(Handle, GWL_EXSTYLE) or WS_EX_APPWINDOW));

          FParentWnd := GetWindowLong(Handle, GWL_HWNDPARENT);
          if FParentWnd <> 0 then
            ShowWindow(FParentWnd, SW_HIDE);

          SetWindowLong(Handle, GWL_HWNDPARENT, 0);
        end;
      SC_RESTORE:
        begin
          SetWindowLong(Handle, GWL_EXSTYLE,
              (GetWindowLong(Handle, GWL_EXSTYLE) and not WS_EX_APPWINDOW));

          if FParentWnd <> 0 then begin
            SetWindowLong(Handle, GWL_HWNDPARENT, FParentWnd);
            ShowWindow(FParentWnd, SW_SHOW);
          end;
        end;
    end;
  end;
  inherited;
end;