vcl - Delphi- Make a EditBox to accept only numbers lessthan or equal to(<=) 12 on Keypress event -

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• only specific numbers in edit box 2 answers

i have edit box , trying make accept numbers 0 12. wrote onexit handler this:

procedure tfrmcourse.edtdurationexit(sender: tobject); begin      if not string.isnullorempty(edtduration.text)           begin             if strtoint(edtduration.text) > 12             begin               edtduration.clear;               edtduration.setfocus;             end;           end; end; 

... want check while typing. tedit should accept numeric input , warn when value > 12.

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final answer

procedure tfrmcourse.edtdurationkeypress(sender: tobject; var key: char); var   stextvalue: string; begin   if sender = edtduration   begin     if (key = formatsettings.decimalseparator) ,       (pos(formatsettings.decimalseparator, edtduration.text) <> 0)       key := #0;      if (charinset(key, ['0' .. '9']))     begin       stextvalue := tedit(sender).text + key;       if stextvalue <> ''       begin         if ((strtofloat(stextvalue) > 12) , (key <> #8))           key := #0;       end;     end   end; end; 

the conversion function strtoint() raises econverterror if entered characters not numeric. can deal setting tedit.numbersonly property. suggest use trystrtoint() function instead (or in addition). although said want check while typing suggest using onchange event, because catches erroneous input pasting clipboard.

procedure tform5.edit1change(sender: tobject); var   ed: tedit;   v: integer; begin   ed := sender tedit;   v := 0;   if (ed.text <> '') ,     (not trystrtoint(ed.text, v) or (v < 0) or (v > 12))   begin     ed.color := $c080ff;     errlabel.caption := 'only numbers 0 - 12 allowed';     exit;   end   else   begin     ed.color := clwindow;     errlabel.caption := '';   end; end; 

the errlabel label near edit box gives user indication of erroneous entry.