Disable the functionality of sizing a form at runtime

Problem/Question/Abstract:

How to disable the functionality of sizing a form at runtime

Answer:

In some cases, developers would want to create a regular window (Form) in Delphi that contains some of the characteristics of a dialog box. For example, they do not want to allow their users to resize the form at runtime due to user interface design issues.

The following example demonstrates a way of handling the Windows message "WM_GetMinMaxInfo" which allows the developer to restrict the size of windows (forms) at runtime to a specific value. In this case, it will be used to disable the functionality of sizing the window (form) at runtime.

unit getminmax;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

type
  TForm1 = class(TForm)

  private
    { Private declarations }
    procedure WMGetMinMaxInfo(var Msg: TWMGetMinMaxInfo); message WM_GETMINMAXINFO;
    procedure WMInitMenuPopup(var Msg: TWMInitMenuPopup); message WM_INITMENUPOPUP;
    procedure WMNCHitTest(var Msg: TWMNCHitTest); message WM_NCHitTest;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.WMGetMinMaxInfo(var Msg: TWMGetMinMaxInfo);
begin
  inherited;
  with Msg.MinMaxInfo^ do
  begin
    ptMinTrackSize.x := form1.width;
    ptMaxTrackSize.x := form1.width;
    ptMinTrackSize.y := form1.height;
    ptMaxTrackSize.y := form1.height;
  end;
end;

procedure TForm1.WMInitMenuPopup(var Msg: TWMInitMenuPopup);
begin
  inherited;
  if Msg.SystemMenu then
    EnableMenuItem(Msg.MenuPopup, SC_SIZE, MF_BYCOMMAND or MF_GRAYED)
end;

procedure TForm1.WMNCHitTest(var Msg: TWMNCHitTest);
begin
  inherited;
  with Msg do
    if Result in [HTLEFT, HTRIGHT, HTBOTTOM, HTBOTTOMRIGHT,
      HTBOTTOMLEFT, HTTOP, HTTOPRIGHT, HTTOPLEFT] then
      Result := HTNOWHERE
end;
end.

A message handler for the windows message "WM_GetMinMaxInfo" in the code above was used to set the minimum and maximum TrackSize of the window to equal the width and height of the form at design time. That was actually enough to disable the resizing of the window (form), but the example went on to handle another couple of messages just to make the application look professional. The first message was the "WMInitMenuPopup" and that was to gray out the size option from the System Menu so that the application does not give the impression that this functionality is available. The second message was the "WMNCHitTest" and that was used to disable the change of the cursor icon whenever the mouse goes over one of the borders of the window (form) for the same reason which is not to give the impression that the resizing functionality is available.