Convert a class string to TClass [duplicate]

This question already has answers here: Closed 11 years ago.

Given the Classes: uses InvokeRegistry; //where TRemotable is defined.

type TMyLabel = class(TRemotable) //some published props TMySubLabel = class(TMyLabel) //more published props

  //some other classes descendent of TMyLabel.

  TMyLabelClass = class of TMyLabel;

My requirement is to implement:

function StringToClass(string aClassName): TClass;
begin
  //your implementation goes here
end;

Usage:

function GetMyLabelInstance(string aClassName):TMy开发者_StackOverflowLabel; 
var
  lCloned: TMyLabel;
begin
  Tclass lClass = StringToClass('TMySubLabel');
  lCloned := TMyLabelClass(lClass).Create;
end;

I am using Delphi 7 and my objects are not derived from TPersistent, thus this solution is not applicable for my case: How to convert classname as string to a class?

Thanks,

---

As your classes are not TPersistent descendants, you have to implement your own RegisterClass/FindClass procedures.

I usually do this by registering the classes with their names in a TStringList (or TDictionary<string, TClass> for newer Delphi versions), as in TOndrej's answer. I do the registration in the initialization section of the unit in which the class is defined.

Then you can have a FindClass function to retrieve the class based on his name, or directly a factory procedure which creates an instance, of the right class based on the name of the class.

I also consider a good practice to pack up the TStringList, the registration procedure and the factory procedure in one class implemented as a singleton.

If you want to use as a factory you also have to add a virtual constructor to the base class (TMyLabel), and define a metaclass type TMyLabelClass = class of TMyLabel, and cast the StringList.Objects[i] to TMyLabelClass instead of TClass