基類窗體要實現的需求包括：控件窗體的字體，權限控制，控制子窗體的顯示范圍，以及其它一些通用方法的聲明。。。。。。

通用方法可聲明為VIRTUAL方法，以允許從它繼承的子窗體

可以OVERRIDE這些方法，達到多態(tài)的效果。

unit uBaseForm;

interface

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

type
  TBaseForm = class(TForm)
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    FRights: string;
    procedure WMGetMinMaxInfo(var Message: TWMGetMinMaxInfo ); message WM_GETMINMAXINFO;//控制子窗體的顯示范圍
  public
    property Rights: string read FRights write FRights;//權限控制
  end;

var
  BaseForm: TBaseForm;

implementation

{$R *.dfm}

procedure TBaseForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caFree;           
end;

procedure TBaseForm.WMGetMinMaxInfo(var Message: TWMGetMinMaxInfo);
begin
  with Message.MinMaxInfo^ do
  begin
    ptMaxPosition.X := Screen.WorkAreaLeft; {Left position when maximized}
    ptMaxPosition.Y := Application.MainForm.Height; {Top position when maximized}
    ptMaxTrackSize.X := Screen.Width; {Maximum width}
    ptMaxTrackSize.Y := screen.WorkAreaHeight - Application.MainForm.Height; {Maximum height}
  end;
  Message.Result := 0; {Tell windows you have changed minmaxinfo}
  inherited;
end;

end.