Question

I have an input edit field where the user can enter data. I want the box width to be at least 191px (min) and maximum 450px (max).

procedure THauptform.edtEingabeChange(Sender: TObject);
begin

// Scale
if Length(edtEingabe.Text) > 8 then
    begin
        if Hauptform.Width <= 450 then
            begin
                verschiebung := verschiebung + 9;
                // The initial values like 'oldedtEingabeWidth' are global vars.
                edtEingabe.Width := oldedtEingabeWidth + verschiebung;
                buDo.Left := oldbuDoLeft + verschiebung;
                Hauptform.Width := oldHauptformWidth + verschiebung;
            end;
    end;
end;

This works for ENTERING text. But when I delete one char, it does not scale back accordingly.

Answer 1

In your code, nothing will happen when your text is less than 8 characters long.

Also, I don’t see any condition under which your width becomes smaller. It only becomes larger (by 9) with each iteration.

By the way, you appear to be multiplying by 9 as an average character width. You can use Canvas.TextWidth to determine the actual width required by the text without estimating.

If you want to use “9” anyway, you should name it as a constant to make clear what it is.

Quick and dirty using TextWidth:

const
   MAX_EINGABE_WIDTH = 450;
   MIN_EINGABE_WIDTH = 191;

procedure THauptform.edtEingabeChange(Sender: TObject);
var Width: Integer;
begin

    // Scale
    Width := edtEingabe.Canvas.TextWidth(edtEingabe.Text);
    if Width > MAX_EINGABE_WIDTH then
       Width := MAX_EINGABE_WIDTH
    else if Width < MIN_EINGABE_WIDTH then
       Width := MIN_EINGABE_WIDTH

    edtEingabe.Width := Width;

end;