XE2做单实例

 1 unit Unit11;

 2 

 3 interface

 4 

 5 uses

 6   Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,

 7   Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

 8 

 9 type

10   TMyTestClass = class

11   private

12     //class var n : integer;

13     class var MyTestClass : TMyTestClass;

14   public

15     function test : string;

16     class function NewInstance: TObject; override;

17     class function GetInstance : TMyTestClass;

18   end;

19 

20 

21 

22   TForm11 = class(TForm)

23     Button1: TButton;

24     procedure Button1Click(Sender: TObject);

25   private

26     { Private declarations }

27   public

28     { Public declarations }

29   end;

30 

31 var

32   Form11: TForm11;

33 

34 implementation

35 

36 {$R *.dfm}

37 

38 procedure TForm11.Button1Click(Sender: TObject);

39 var

40   a : TMyTestClass;

41 begin

42   {两种方式均可，但GetInstance貌似更能清晰表面这个类是单实例。}

43   {a := TMyTestClass.Create;}

44   a := TMyTestClass.GetInstance;

45   if a <> nil then

46     Application.MessageBox(PChar(a.test), '提示信息', mb_OK);

47 end;

48 

49 { TMyTestClass }

50 

51 class function TMyTestClass.GetInstance: TMyTestClass;

52 begin

53   Result := TMyTestClass.Create;

54 end;

55 

56 class function TMyTestClass.NewInstance: TObject;

57 begin

58 //  if n = 1 then

59 //  begin

60 //    Result := nil;

61 //    raise Exception.Create('只能创建1个实例');

62 //  end

63 //  else

64 //  begin

65 //    Result := inherited NewInstance;

66 //    Inc(n);

67 //  end;

68   if MyTestClass <> nil then

69   begin

70     Result := MyTestClass;

71   end

72   else

73   begin

74     Result := inherited NewInstance;

75     MyTestClass := Result as TMyTestClass;

76   end;

77 end;

78 

79 function TMyTestClass.test: string;

80 begin

81   Result := Self.ClassName;

82 end;

83 

84 end.

类变量+NewInstance实现单实例，真是太Easy了。