Question

Most TWinControl descendant in Delphi has an override method CreateParams to define it’s subclass such as: ‘EDIT’, ‘COMBOBOX’, ‘BUTTON’, ‘RICHEDIT’ and etc.

CreateSubClass(Params, 'EDIT');
CreateSubClass(Params, 'COMBOBOX');
CreateSubClass(Params, 'BUTTON');

There are quite a number of rich edit control for Delphi including controls from third party vendors. All those controls are sub class of RichEdit.

I am wondering if there is a way to test a control is RichEdit regardless of it’s original vendor by testing the SubClass defined in CreateParams?

Answer 1

Thanks for all the feedback. I think there is no way to get the windows class name for the TWinControl.

Here is another version of IsRichEdit modified from JamesB’s version:

type TWinControlAccess = class(TWinControl);

function IsRichEdit(C: TWinControl): boolean;

const A: array[0..8] of string = (
           'RICHEDIT',
           'RICHEDIT20A', 'RICHEDIT20W',
           'RICHEDIT30A', 'RICHEDIT30W',
           'RICHEDIT41A', 'RICHEDIT41W',
           'RICHEDIT50A', 'RICHEDIT50W'
          );

var Info: TWNDClass;
    p: pointer;
    s: string;
begin
  p := TWinControlAccess(C).DefWndProc;

  Result := False;

  for s in A do begin
    if GetClassInfo(HInstance, PChar(s), Info) and (Info.lpfnWndProc = p) then begin
      Result := True;
      Break;
    end;
  end;
end;

We may modify array A if there is newer version of RichEdit class from Windows.

Another possible but risky solution is I just check if the control’s VCL class name contain ‘RichEdit’ string as almost rich edit VCL class from Delphi or 3rd party vendors name the controls that way.