Delphi: How to know when a TEdit changes size?

Question

i need to update items around an edit box when it changes size.

TEdit has no OnResize event.

An edit box can resize at various times, e.g.:

• changing width/height in code
• form scaled for DPI scaling
• font changed

And i'm sure others i don't know about.

i need a single event to know when an edit box has changed its size. Is there a Windows message i can subclass the edit box for and grab?

Answer 1

OnResize is declared as a protected property of TControl. You could expose it using a so-called "cracker" class. It's a bit of a hack, though.

type
  TControlCracker = class(TControl);

...

procedure TForm1.FormCreate(Sender: TObject);
begin
  TControlCracker(Edit1).OnResize := MyEditResize;
end;

procedure TForm1.MyEditResize(Sender: TObject);
begin
  Memo1.Lines.Add(IntToStr(Edit1.Width));
end;