Prevent user from typing invalid values in QLineEdit

wakiki

I'm trying to to use QDoubleValidator to prevent user from typing invalid values, or values which are out of range, in QLineEdit.
Im not sure if validators suppose to block entering wrong values while typing or only when the user press "Enter" or release focus.
(docu says: ...The user may change the content to any Intermediate value during editing, but will be prevented from editing the text to a value that v validates as Invalid. ..)
I need a solution which prevents the user from typing any invalid values.
I tried something like this:

_validator(new QDoubleValidator(0.0, 10.0, 5, this))
_validator->setNotation(QDoubleValidator::StandardNotation);
_validator->setLocale(QLocale::C);
setValidator(_validator);

But i can still enter numbers up to 99.
Decimal check seems to work and hasAcceptableInput() works also correctly.
It returns false for values higher than 10.0, when i add signal/slot connection for textChanged().

JonB

@wakiki
Hello and welcome.

Since you seem to be accepting floating point numbers from the user, before you proceed with QLineEdit did you see QDoubleSpinBox as your starting point?

wakiki

@JonB
I would rather avoid changing the widget type, but i will check that.
Is it possible to show a string in QDoubleSpinBox? I want to add something like ".sec" behind the number.

JonB

@wakiki said in Prevent user from typing invalid values in QLineEdit:

I would rather avoid changing the widget type, but i will check that.

Odd. Why do you want a QLineEdit for editing a number when it is not designed for that, QDoubleSpinBox is and has range validation built into it?

Is it possible to show a string in QDoubleSpinBox? I want to add something like ".sec" behind the number.

How do you do this at present with a QLineEdit which has a QDoubleValidator? If the user types in .sec it won't validate as a number? Or do you mean you put .sec somewhere outside the widget (e.g. in a QLabel), in which case it does not affect which widget you use? Or, QDoubleSpinBox has an optional prefix/suffix, is that what you are wanting for your .sec?

Meanwhile, QDoubleValidator::validate() says

Returns Intermediate if input contains a double that is outside the range or is in the wrong format; e.g. is empty.

so I am guessing that is what you get when you enter 99.

wakiki

Currently my QLineEdit has no validator at all. Its handled after editing is finished. I guess you are right,
QDoubleSpinBox with a suffix would be the best solution in this case.

We used QLineEdit for all editable double parameters so far. I don't know why, but live typing validation was not a required feature,
so i will stick with QLineEdit.

JonB

@wakiki
Fair enough. I think you will find the validator prevents the user from typing some things --- for example invalid characters or a string which is too long --- but it won't for example prevent things being typed which could be changed or adjusted to be right. I'm not sure what the rules are. It will just return Intermediate for the verification.