Roll up and restore a TForm when clicking on the title bar

Problem/Question/Abstract:

How to roll up and restore a TForm when clicking on the title bar

Answer:

The standard behaviour for double clicking a title bar is to maximize/ restore the form. The following class changes the double click action to add a new effect which is RollUp/ Restore. Copy the following unit and place it in a directory which is recognised by Delphi's search path.

unit OrckaForm;

interface

{$B-}

uses
  Messages, Forms, Classes;

type
  TOrckaForm = class(TForm)
  private
    FOldHeight: Longint;
    FRollUp, FRolledUp: Boolean;
  protected
    procedure WMNCLDblClick(var Msg: TMessage); message WM_NCLBUTTONDBLCLK;
    procedure WMGetMinMaxInfo(var Msg: TMessage); message WM_GETMINMAXINFO;
  public
    constructor Create(AOwner: TComponent); override;
    property RollUp: Boolean read FRollUp write FRollUp;
  end;

implementation

uses
  Windows;

procedure TOrckaForm.WMNCLDblClick(var Msg: TMessage);
begin
  if (Msg.wParam = HTCAPTION) and (FRollUp) then
  begin
    if FRolledUp then
    begin
      FRolledUp := False;
      Height := FOldHeight;
    end
    else
    begin
      FRolledUp := True;
      FOldHeight := Height;
      Height := 0
    end;
  end
  else
    inherited;
end;

constructor TOrckaForm.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FOldHeight := Height;
  FRollUp := True;
  FRolledUp := False;
end;

procedure TOrckaForm.WMGetMinMaxInfo(var Msg: TMessage);
begin
  inherited;
  if FRolledUp then
    pMinMaxInfo(Msg.lParam)^.ptMaxTrackSize.y := Height;
end;

end.

To use the form create a new form which will look something like..

unit Unit3;

interface

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

type
  TForm3 = class(TForm)
  private
    { Private declarations }

Add OrckaForm to the uses clause and change the following line

TForm3 = class(TForm)

to

TForm3 = class(TOrckaForm)

Run your project, whenever you double click the title the form will roll up/ restore.