Delphi 以類別名稱來建立物件

http://www.wretch.cc/blog/solnone/14198678

若想用父類別來操作，而不想 use 各子類別，則可以類別名稱來動態建立子類別物件
在 unit Classes 中，有RegisterClass, GetClass, FindClass 和 UnRegisterClass
先使用 RegisterClass 註冊所需動態建立的類別
然後才能使用 GetClass 或 FindClass 以類別名稱來找出註冊過的類別
再轉型為所需的父類別來建立並使用物件
若不再需要它，則可以使用 UnRegisterClass 來取消註冊

procedure TForm1.FormCreate(Sender: TObject);
var
PClass: TPersistentClass;
Strings: TStrings;
begin
  PClass := FindClass('TStringList');
  Strings := PClass.Create as TStrings;
  try
    Strings.Add('Hi');
  finally
    Strings.Free;
  end;
end;

initialization
RegisterClass(TStringList);

finalization
UnRegisterClass(TStringList);

﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍﹍

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  end;

  TMyParent = class(TComponent)
  public
    function echo(name: string): string; virtual; abstract;
  end;

  TMyParentClass = class of TMyParent;

  TMySub1 = class(TMyParent)
  private
    s: string;
  public
     constructor Create(AOwner: TComponent); override;
     function echo(name: string): string; override;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  PClass: TPersistentClass;
  Obj: TMyParent;
begin
  RegisterClass(TMySub1);
  PClass := FindClass('TMySub1');
  Obj := TMyParentClass(PClass).Create(Self);
  Caption := Obj.echo('Solnone');
  UnRegisterClass(TMySub1);
end;

{ TMySub1 }

constructor TMySub1.Create(AOwner: TComponent);
begin

  s := AOwner.GetNamePath + ' TMySub1 ';
end;

function TMySub1.echo(name: string): string;
begin
  Result := s+ 'Hello ' + name;
end;

end.

轉貼至 http://chuanitai.pixnet.net/blog/post/37036289-delphi-%E4%BB%A5%E9%A1%9E%E5%88%A5%E5%90%8D%E7%A8%B1%E4%BE%86%E5%BB%BA%E7%AB%8B%E7%89%A9%E4%BB%B6