非模式窗體從創建到銷毀都需要代碼來維護，防止內存未安全釋放。

模式窗體就比較省心一些，只需要在代碼段的try…finally中創建並維護即可。

下面用例子來說明一下兩類窗體如何調用：

主窗體程序：

unit Main;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls,ModalForm,ModalessForm;
 
type
  TForm8 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    
 
procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form8: TForm8;
 
implementation
 
{$R *.dfm}
 
procedure TForm8.Button1Click(Sender: TObject);
begin
  try
 

    Form9:=TForm9.Create(Application);
    Form9.ShowModal;
  finally
    Form9.Free; //窗體的清理放在同一代碼段的try...finaally中，而不是在ModalForm中的Destroy方法裏。
    Form9:=nil;
  end;
 
end;
 
procedure TForm8.Button2Click(Sender: TObject);
begin
  if not Assigned(Form10) then  //防止出現多個窗體實例
  Form10:=TForm10.Create
 
(Application); //窗體的創建方式
 
  Form10.Show;
end;
 
end.

模式窗體：

unit ModalForm;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;
 
type
  TForm9 = class(TForm)
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form9: TForm9;
 
implementation
 
{$R *.dfm}
 
 
end.

非模式窗體：

unit ModalessForm;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;
 
type
  TForm10 = class(TForm)
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form10: TForm10;
 
implementation
 
{$R *.dfm}
 
procedure TForm10.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action:=caFree;
end;
 
procedure TForm10.FormDestroy(Sender: TObject);
begin
  Form10:=nil; //這裏是Form10設為nil而不是TForm10，否則將無法再次創建窗體。
end;
 
end.

模式窗體與非模式窗體