How do I disable special handling of & on Qt button labels?

Question

I have inherited a virtual keyboard system with an array of buttons, one for each key. The label for each button is a single QChar. When showing the "symbols" keyboard, the code uses an '&' QChar for a key label, but the key shows as blank. I'm sure Qt is processing the '&' as a shortcut key prefix. Similarly, the entered text is shown on another, longer, button label; this label, as well, handles '&' character as an accelerator. Entering "ABC&DEF" is shown as "ABCDEF" with the 'D' underlined.

I have tried building with QT_NO_SHORTCUT #defined, but that made no difference.

Does anyone know of an easy way to disable this special handling of '&'?

Answer 1

The answer is found in Qt doc. QAbstractButton::text:

If the text contains an ampersand character ('&'), a shortcut is automatically created for it. The character that follows the '&' will be used as the shortcut key. Any previous shortcut will be overwritten or cleared if no shortcut is defined by the text. See the QShortcut documentation for details. To display an actual ampersand, use '&&'.

(Emphasize by me.)

QPushButton is derived from QAbstractButton inheriting this behavior.

Sample testQPushButtonAmp.cc:

#include <QtWidgets>

int main(int argc, char **argv)
{
  qDebug() << "Qt Version:" << QT_VERSION_STR;
  QApplication app(argc, argv);
  QPushButton qBtn("Text with &&");
  qBtn.show();
  return app.exec();
}

testQPushButtonAmp.pro:

SOURCES = testQPushButtonAmp.cc

QT = widgets

Compiled and tested on cygwin64 on Windows 10:

$ qmake-qt5 testQPushButtonAmp.pro

$ make

$ ./testQPushButtonAmp
Qt Version: 5.9.4

---

Concerning how to disable this default behavior:

I had a look at woboq.org QAbstractButton::setText().

void QAbstractButton::setText(const QString &text)
{
    Q_D(QAbstractButton);
    if (d->text == text)
        return;
    d->text = text;
#ifndef QT_NO_SHORTCUT
    QKeySequence newMnemonic = QKeySequence::mnemonic(text);
    setShortcut(newMnemonic);
#endif
    d->sizeHint = QSize();
    update();
    updateGeometry();
#ifndef QT_NO_ACCESSIBILITY
    QAccessibleEvent event(this, QAccessible::NameChanged);
    QAccessible::updateAccessibility(&event);
#endif
}

So, QT_NO_SHORTCUT disables to retrieve the shortcut out of text but it has to be defined when Qt library is built from source. Actually, I'm afraid even with disabled shortcuts, the single & will still become invisible in output.

I digged deeper in woboq.org and found some promising candidates e.g.:

qt_set_sequence_auto_menmonic()

Specifies whether mnemonics for menu items, labels, etc., should be honored or not. On Windows and X11, this feature is on by default; on macOS, it is off. When this feature is off (that is, when b is false), QKeySequence::mnemonic() always returns an empty string.

Note: This function is not declared in any of Qt's header files. To use it in your application, declare the function prototype before calling it.

and a sample in QProxyStyle

#include "textedit.h"
#include <QApplication>
#include <QProxyStyle>

class MyProxyStyle : public QProxyStyle
{
  public:
    int styleHint(StyleHint hint, const QStyleOption *option = 0,
                  const QWidget *widget = 0, QStyleHintReturn *returnData = 0) const override
    {
        if (hint == QStyle::SH_UnderlineShortcut)
            return 0;
        return QProxyStyle::styleHint(hint, option, widget, returnData);
    }
};

int main(int argc, char **argv)
{
    Q_INIT_RESOURCE(textedit);

    QApplication a(argc, argv);
    a.setStyle(new MyProxyStyle);
    TextEdit mw;
    mw.resize(700, 800);
    mw.show();
    //...
}

which I tried in my sample.

Finally, nothing of them achieved the desired effect, i.e. only "&&" was rendered as & but "&" never.

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