MaxLength property has no effect when setting text in code

Question

I noticed that when I set the MaxLength property of an Edit or DBEdit control, this does not stop me from putting text on the control larger than the MaxLength in code.

When I set the MaxLength = 12 for example, then

• I cannot enter a longer value using the keyboard
• I cannot paste a longer text using copy/paste

but I can do this :

Edit1.Text := '012345678901234567890123456789'

Is this normal behaviour ? Is this also so in Delphi Tokyo ?
And more important, is there an easy way to prevent this ?

Answer 1

It is the same in 10.2. Tokyo. The property TEdit.Text is inherited unchanged from TControl (through TCustomEdit and TWinControl). And TControl.SetText does not know anything about MaxLength, so it does not limit the text length. It indirectly issues a CM_TEXTCHANGED message, but TCustomEdit, which intercepts this, does not use that to limit the text length either.

The only way to prevent this is probably not to assign anything longer than 12 "characters", or to subclass TCustomEdit into your own TMyEdit, do the check in your own SetText procedure, install the component and use that instead.