How to test if a control is a RichEdit control

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

Am I missing something? Is it not simply a case of testing:

if (MyControl is TRichEdit)

or

if (MyControl is TCustomRichEdit)

Answer 2

Use the Win32 API GetWindowClass() function and then check for the various rich edit class versions that are available - 'RICHEDIT' (1.0), 'RICHEDIT20A' or 'RICHEDIT20W' (2.x+), and 'RICHEDIT50W' (4.1).

Answer 3

You could use

 function GetClassInfo(hInstance: HINST; lpClassName: PChar;  var lpWndClass: TWndClass): BOOL;

I think this is what Remy was trying to do.

something like:

Function IsRichEdit(MyControl : TWinControl):Boolean;
var 
    Info : TWNDClass;
begin
    Result := False;
    if GetClassInfo(HInstance,PCHAR('RICHEDIT'),Info) and (Info.lpfnWndProc = MyControl.DefWndProc) then 
        Result := True
    else if GetClassInfo(HInstance,PCHAR('RICHEDIT20A'),Info) and (Info.lpfnWndProc = MyControl.DefWndProc)  then 
        Result := True
    else if GetClassInfo(HInstance,PCHAR('RICHEDIT30A'),Info) and (Info.lpfnWndProc = MyControl.DefWndProc)  then 
        Result := True
    else if GetClassInfo(HInstance,PCHAR('RICHEDIT41A'),Info) and (Info.lpfnWndProc = MyControl.DefWndProc)  then 
        Result := True
    else if GetClassInfo(HInstance,PCHAR('RICHEDIT50A'),Info) and (Info.lpfnWndProc = MyControl.DefWndProc)  then 
        Result := True
end;

If you are using Delphi > 2007 then you might need to test for the 'W'(unicode) versions as well e.g 'RICHEDIT20W'

Edit: added Info.WndProc test to match the control.

Oddly enough this won't work for the cxControls since the cxRichEdit isn't the control using the rich edit window (It's a containing so you would need to pass cxControl.InnerControl for this to return true).

Edit I couldn't get this to work for more than the first richedit control created.

Answer 4

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.