Question

I’d like to instantiate a class but I only have its name in a string. Is there a way?

Answer 1

This is from Delphi help (Delphi 2006, but also available from at least Delphi 7):

Syntax function GetClass(const AClassName: string): TPersistentClass;

Description Call GetClass to obtain a class from a class name. This class can be used as a parameter to routines that require a class. The Class must be registered before GetClass can find it. Form classes and component classes that are referenced in a form declaration (instance variables) are automatically registered when the form is loaded. Other classes can be registered by calling RegisterClass or RegisterClasses .

Here some sample code. Works as such only because TButton is a TControl and therefore the typecast is valid.

procedure TForm1.FormCreate(Sender: TObject); begin   RegisterClasses([TButton, TForm]); end;  procedure TForm1.Button1Click(Sender: TObject); var   CRef : TPersistentClass;   AControl : TControl; begin   CRef := GetClass('TButton');   if CRef<>nil then   begin      AControl := TControl(TControlClass(CRef).Create(Self));      with AControl do      begin         Parent := Self;         Width := 50;         Height := 30;      end;   end; end;