查看完整版本: Delphi 类的静态属性

Delphi 类的静态属性

　　


                  Because Delphi not provide static member for our using, so if you want a static

member of class in Delphi what should I do ?

Ok! At least there are three ways to implement this.

1,Using private global variant(in implement section of unit),but there are a lit


visibility scope in project or unit.

2,Using global variant, a more visibility scope in project or unit.a lit same as


above.

3,Using typed constant,just using compiler directive $J  or Project properties


|compiler Option Typed constant.

There are some simple source code as follows:


unit Unit1;


interface


uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, StdCtrls;


type

TForm1 = class(TForm)

Button1: TButton;

procedure Button1Click(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;


TStaticMemberObject = class

private

class procedure SetName(const Value: string);

class function GetName: string;

class function StaticMethod(ReadFlag: boolean; var Value: string):boolean;

published

property Name: string read GetName write SetName;

end;


var

Form1: TForm1;


implementation


{$r *.dfm}


{ TStaticMemberObject }


class function TStaticMemberObject.StaticMethod(ReadFlag: boolean;

var Value: string): boolean;

const static: string = '';

begin

result := True;

if ReadFlag then

Value := static

else

static := value;

end;




class function TStaticMemberObject.GetName: string;

var

Value: string;

begin

StaticMethod(true, Value);

result := Value;

end;


class procedure TStaticMemberObject.SetName(const Value: string);

var

setvalue: string;

begin

setvalue := Value;

StaticMethod(false, setvalue);

end;


procedure TForm1.Button1Click(Sender: TObject);

var

so: TStaticMemberObject;

begin

so.Name := 'Hello, my static property!';

ShowMessage(so.Name);

so.SetName('hi, my static property!');

ShowMessage(so.GetName);

end;


end.


Please pay attention to the class method used here. The Name property's modifiers


both use class method. In fact if you use normal static method with no class


directive the code still works well. like this:

procedure SetName(const Value: string);

function GetName: string;

Because we do not access other fields and other instance methods of this


tstaticmemberobject class or some object of TStaticMemberObject type, so there is


no AV using normal static method.

OK, if you need this trick just try it.