Allow entry in QLineEdit only within range of QDoubleValidator

Question

I have a set of QLineEdits that are supposed to accept double values within a certain range, (e.g., -15 to 15).

I have something along these lines when

Answer 1

It is possible to do this also without subclassing.

lineEdit = new QLineEdit();
connect(lineEdit,SIGNAL(textChanged(QString)), this, SLOT(textChangedSlot(QString)));

QDoubleValidator *dblVal = new QDoubleValidator(minVal, maxVal, 1000, lineEdit);
dblVal->setNotation(QDoubleValidator::StandardNotation);
dblVal->setLocale(QLocale::C);
lineEdit->setValidator(dblVal);

Setting of the locale may be important because it defines which characters are interpreted as a decimal separator. Format of the input string defines which locales should be used.

In the textChangedSlot, we can validate input this way:

QString str = lineEdit->text();
int i = 0;
QDoubleValidator *val = (QDoubleValidator *) lineEdit->validator();
QValidator::State st = val->validate(str, i);

if (st == QValidator::Acceptable) {
    // Validation OK
} else {
    // Validation NOK
}

In this case also QValidator::Intermediate state is interpreted as a failed case.

If we connect textChanged -signal to the textChangedSlot, validation is done after every input field change. We could also connect editingFinished() or returnPressed() -signals to the validation slot. In that case, validation is done only when user stops editing the string.