I'm trying to set up a text edit that does the shift tab remove indentation thing that code editors do; but i can't respond to shift tab because it changes the widget focus.

I tried overriding the event function in the main window and that didn't work; then i tried event filters on all widgets and that didn't work; then i tried overriding QApplication::notify like so:

class MyApplication : public QApplication
{
    Q_OBJECT
public:
    MyApplication(int argc, char *argv[]) : QApplication(argc, argv) { }
    virtual ~MyApplication() = default;

    bool    notify(QObject * o, QEvent *e) override
    {
        if (e->type() == QEvent::KeyPress)
        {
            QKeyEvent* k = static_cast<QKeyEvent*>(e);

            if (k->key() == Qt::Key_Tab && dynamic_cast<QPlainTextEdit*>(focusWidget()))
            {
                // filter tab out
                return false;
            }
        }

        return QApplication::notify(o, e);
    }
};

And that didn't work; and additionally it crashes in QCoreApplication::arguments unless I run the application from inside valgrind for some reason.

Regardless I'm out of ideas, how can i stop shift tab from changing focus?

CodePudding user response：

If you are using QTextEdit or QPlainTextEdit, which is quite likely, you can set the Tab behavior using tabChangesFocus property. See https://doc.qt.io/qt-6/qtextedit.html#tabChangesFocus-prop and https://doc.qt.io/qt-6/qplaintextedit.html#tabChangesFocus-prop

CodePudding user response：

I was able to implement the desired behavior in Qt's included qtbase/examples/widgets/widgets/lineedits example program, by inserting the following code into main.cpp, just above int main(int, char **):

class BackTabFilter : public QObject
{
public:
   BackTabFilter(QObject * parent) : QObject(parent)
   {
      qApp->installEventFilter(this);
   }

   virtual bool eventFilter(QObject * watched, QEvent * e)
   {
      if ((e->type() == QEvent::KeyPress)&&(static_cast<QKeyEvent *>(e)->key() == Qt::Key_Backtab))
      {
         QLineEdit * le = dynamic_cast<QLineEdit *>(qApp->focusWidget());
         if (le)
         {
            le->setText(le->text()   " Bork!");
            return true;  // eat this event
         }
      }
      return QObject::eventFilter(watched, e);
   }
};

.... and then adding this line into main() itself (just below the QApplication app(argc,argv); line):

BackTabFilter btf(NULL);

With these changes, pressing shift-Tab while the focus is on one of the QLineEdits in the GUI causes the word "Bork!" to be appended to the QLineEdit's text, rather than having the widget-focus change.