Mega Code Archive
Static property of class in Delphi
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Title: static property of class in Delphi
Question: static property of class
Answer:
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.
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