Is there a way to instantiate a class by its name in delphi?

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 CRefnil then begin AControl := TControl(TControlClass(CRef). Create(Self)); with AControl do begin Parent := Self; Width := 50; Height := 30; end; end; end.

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 CRefnil then begin AControl := TControl(TControlClass(CRef). Create(Self)); with AControl do begin Parent := Self; Width := 50; Height := 30; end; end; end.

Great solution. But now I've ran into another issue. The class I'd like to instantiate is a class of my own that implements an Interface.

And registerClass must be called with a persistent class. Any idea? – Ricardo Acras Mar 31 '09 at 14:12 Is it possible to derive your class or one of it's ancestors from TPersistent?

– malach Mar 31 '09 at 14:28 I don't believe so, since it implements a interface and it has to derive from TInterfaceObject – Ricardo Acras Mar 31 '09 at 14:29 I fount TInterfacedPersistent, just perfect. Thanks. – Ricardo Acras Mar 31 '09 at 14:51 Never mind my previous suggestion.

TInterfacedPersistent is what you want. I thought it existed but couldn't remember the name. – Jim McKeeth Mar 31 '09 at 15:47.

When I needed to do that, I Built my own Object Factory that uses a specially subclassed TStringList, I'm currently using Delphi 7 so the string list class supports only attach a Object to a String, then I got to subclass TStringList to make it possible handle Class Types too, so now I can instantiate a object just passing it's class name to the factory. Works that way: 1st - Load a Singleton Object Factory; 2st - Register any object to the factory, could be in the initialization section of the unit; The main Factory's methods could be: isClassRegistered, registerClass, instantiateClass(ClassName: STring): TObject; This way I can instantiate any object, or use a previous instantiated object, or even, a subset of they. I rather use a Enumerated type instead of a string to identify a Class.

Remarks: It's a very, very terse example, a completely functional code is more complex, but, belive me, not too much.

I reused the code above: . .. TTripple=class (TPersistent) private FFont:TFont; public constructor Create; Destructor Destroy;override; published property Font:TFont read FFont write FFont; end; var Form1: TForm1; implementation {$R *. Dfm} constructor TTripple.

Create; begin inherited; FFont:=TFont. Create; end; destructor TTripple. Destroy; begin FFont.

Free; inherited; end; procedure TForm1. FormCreate(Sender: TObject); begin RegisterClasses(TButton, TForm, TTripple); end; procedure TForm1. Button1Click(Sender: TObject); var CRef : TPersistentClass; APer : TPersistent; begin CRef := GetClass('TTripple'); if CRefnil then begin APer := TPersistent(TPersistentClass(CRef).

Create); ShowMessage(APer. ClassName); // TTriple (correct) if APer is TTripple then (APer as TTripple).Font. Color:=90; /// Here I get error message, because TTriple was not created yet...?!?!?!

End; end.

This is not how StackOverflow works. If you have a question that relates to an earlier one, please ask a new question while providing a link to the one you are referring to. – mghie Dec 7 '09 at 21:53.

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