Get class by its name in Delphi

Question

I would like to write a function that accepts a classname and results the corresponding TClass. I've noticed that, System.Classes.GetClass function doesn't works if the classname isn't registered.

Example:

if(GetClass('TButton') = nil)
then ShowMessage('TButton not found!')
else ShowMessage('TButton found!');

The previous code always shows:

TButton not found!

Is there something missing?

Answer 1

You can get unregistered class used in Delphi application via extended RTTI. But you have to use fully qualified class name to find the class. TButton will not be enough, you have to search for Vcl.StdCtrls.TButton

uses
  System.Classes,
  System.RTTI;

var
  c: TClass;
  ctx: TRttiContext;
  typ: TRttiType;
begin
  ctx := TRttiContext.Create;
  typ := ctx.FindType('Vcl.StdCtrls.TButton');
  if (typ <> nil) and (typ.IsInstance) then c := typ.AsInstance.MetaClassType;
  ctx.Free;
end;

Registering class ensures that class will be compiled into Delphi application. If class is not used anywhere in code and is not registered, it will not be present in application and extended RTTI will be of any use in that case.

Additional function that will return any class (registered or unregistered) without using fully qualified class name:

uses
  System.StrUtils,
  System.Classes,
  System.RTTI;

function FindAnyClass(const Name: string): TClass;
var
  ctx: TRttiContext;
  typ: TRttiType;
  list: TArray<TRttiType>;
begin
  Result := nil;
  ctx := TRttiContext.Create;
  list := ctx.GetTypes;
  for typ in list do
    begin
      if typ.IsInstance and (EndsText(Name, typ.Name)) then
        begin
          Result := typ.AsInstance.MetaClassType;
          break;
        end;
    end;
  ctx.Free;
end;