Qt Example with HexStringValidator fails - qt

Question

I am using the following code from this example: https://doc.qt.io/qt-5/qtserialbus-can-example.html
enum {
MaxPayload = 8,
MaxPayloadFd = 64
};
HexStringValidator::HexStringValidator(QObject *parent) :
QValidator(parent),
m_maxLength(MaxPayload)
{
}
HexStringValidator::HexStringValidator(QObject *parent, uint maxLength) :
QValidator(parent),
m_maxLength(maxLength)
{
}
class HexStringValidator : public QValidator
{
Q_OBJECT
public:
explicit HexStringValidator(QObject *parent = nullptr);
explicit HexStringValidator(QObject *parent, uint maxLength);
QValidator::State validate(QString &input, int &pos) const;
void setMaxLength(int maxLength);
private:
uint m_maxLength = 0;
};
The problem is in this function:
I have a lineedit with this validator and call it with a valid Hex String.
ui->lineEditCANCommand->setValidator(new HexStringValidator(this, 4));
ui->lineEditCANCommand->setText("000003e9");
QValidator::State HexStringValidator::validate(QString &input, int &pos) const
{
const int maxSize = 2 * static_cast<int>(m_maxLength);
const QChar space = QLatin1Char(' ');
QString data = input;
data.remove(space);
if (data.isEmpty())
return Intermediate;
// limit maximum size and forbid trailing spaces
if ((data.size() > maxSize) || (data.size() == maxSize && input.endsWith(space)))
return Invalid;
// check if all input is valid
const QRegularExpression re(QStringLiteral("^[[:xdigit:]]*$"));
if (!re.match(data).hasMatch())
return Invalid;
// insert a space after every two hex nibbles
const QRegularExpression insertSpace(QStringLiteral("(?:[[:xdigit:]]{2} )*[[:xdigit:]]{3}"));
if (insertSpace.match(input).hasMatch()) {
input.insert(input.size() - 1, space);
pos = input.size();
}
return Acceptable;
}
The function is supposed to change this to "00 00 03 e9"
It however runs endless and creates
000003e 9
000003e 9
000003e 9
000003e 9
What is going wrong? Note, this code is from Qt and not mine.

Answer 1

In Qt6 problem should be gone.
There was related to this problem issue and two following commits:
Can example: Fix crash in payload hex editor,
CAN Example: Properly format payload hex string
It is possible to test since Qt 6.2.0.
First, I changed insertSpace regular expression to threeDigits:
QStringLiteral("[[:xdigit:]]{3}")
and insert space if 3 digits were added sequentially:
input.insert(match.capturedEnd() - 1, space);
That solves crash problem (infinite recursion).
Then I added auxilliary condition isEvenHex and formatter formatHexData with oneDigitAndSpace and threeDigits regular expressions that removes all extra spaces and add space after every two hex nibbles. I call them respectively on text change and sendButton click:
connect(m_ui->payloadEdit, &QLineEdit::textChanged, frameIdOrPayloadChanged);
connect(m_ui->sendButton, &QPushButton::clicked, [this]() {
...
m_ui->payloadEdit->setText(formatHexData(data));
...
}
Trying to solve your task I added:
QValidator::State HexStringValidator::validate(QString &input, int &pos) const
{
...
QString data = input;
const QRegularExpression twoSpaces(QStringLiteral("([\\s]{2})"));
if (twoSpaces.match(data).hasMatch())
return Invalid;
data.remove(space);
...
But there is one problem: if you are editing string in payload editor you may remove digits and two spaces can occure. The validator won't allow you remove characters between spaces. As a compromise I would introduce
threeSpaces(QStringLiteral("([\\s]{3})"));
validator instead of twoSpaces. With that one you may enter two spaces sequentially but still can edit string. I may ask QtSerialBus developers to include that change too.