Add item to combobox when it is "touched"

[ademmler]

I would like to add a list of items (as example a list of files in a folder) to a combobox
dynamically when the user clicks on this combobox.

I tried this - by the way how would this be in the new syntax?

connect(ui->combo_Measurements, SIGNAL(aboutToShow()), this, SLOT(slotGetMeasurementsList()));

And I tried:

void MyApp::on_combo_Measurements_highlighted(int index)
{
  QStringList files = measurementsFolder.entryList(QStringList() << "*.*", QDir::Files);
    ui->combo_Measurements->clear();
    if(! files.isEmpty()) {
        foreach (QString fileName, files) {
            QString filePath = QDir::toNativeSeparators(measurementsFolder.filePath(fileName));
            ui->combo_Measurements->addItem(fileName, filePath);
        }
    }
}

The later is partially "working" but I cant select any entry then, because the actualisation takes permanently place. Therefore I am looking for the better (correct) way of doing this.

[Pl45m4]

@ademmler said in Add item to combobox when it is "touched":

connect(ui->combo_Measurements, SIGNAL(aboutToShow()), this, SLOT(slotGetMeasurementsList()));

What is this signal?
IIRC aboutToShow() is a signal from QMenu. There is nothing like that in QComboBox.

he later is partially "working" but I cant select any entry then, because the actualisation takes permanently place

Then don't choose the highlighted signal as trigger for your code.
Put it in some extra function and call this function in mousePressEvent, for example.

Or work with QComboBox ability to display model data. Create a model which holds your data and let the QComboBox view display it.

• https://doc.qt.io/qt-6/qcombobox.html#model-view-framework

[ademmler]

@Pl45m4 said in Add item to combobox when it is "touched":

Hi, thx for your feedback.

@ademmler said in Add item to combobox when it is "touched":

connect(ui->combo_Measurements, SIGNAL(aboutToShow()), this, SLOT(slotGetMeasurementsList()));

What is this signal?
IIRC aboutToShow() is a signal from QMenu. There is nothing like that in QComboBox.

This was simply a try - because with menus for example it works and the compiler/Qt did not complained about this.

he later is partially "working" but I cant select any entry then, because the actualisation takes permanently place

Then don't choose the highlighted signal as trigger for your code.
Put it in some extra function and call this function in mousePressEvent, for example.

Or work with QComboBox ability to display model data. Create a model which holds your data and let the QComboBox view display it.

• https://doc.qt.io/qt-6/qcombobox.html#model-view-framework

Ok, thx for the hint. I actually try this and it seems to work:

ui->combo_Measurements->installEventFilter(this);
....
bool MyApp::eventFilter(QObject *f_object, QEvent *f_event){
   if(f_object == ui->combo_Measurements){
       if(f_event->type() == QEvent::MouseButtonPress){
           slotGetMeasurementsList(); 
       }
       return false;
   }
   return false;
}

[JonB]

@ademmler said in Add item to combobox when it is "touched":

This was simply a try - because with menus for example it works and the compiler/Qt did not complained about this.

Do not ever use old-style signal/slot syntax. It was replaced over a decade ago.

connect(ui->combo_Measurements, SIGNAL(aboutToShow()), this, SLOT(slotGetMeasurementsList()));
# replace by
connect(ui->combo_Measurements, &QMenu::aboutToShow, this, &ThisClass::slotGetMeasurementsList);

If you did this you would see, and the compiler would complain, that QMenu::aboutToShow does not go with ui->combo_Measurements, which is presumably a QComboBox.

[Pl45m4]

@ademmler said in Add item to combobox when it is "touched":

This was simply a try - because with menus for example it works and the compiler/Qt did not complained about this.

Haha, you can't just throw signals and classes together at random. It won't work like this ;-)
I think you know that :)

It doesn't complain, because the string based (with SIGNAL and SLOT) connection does not perform a check (signal + slot compatible, signal/slot valid, matching args, etc...) while compiling.
Like @JonB said, do yourself a favor and stop using this type of connection ;-)
With function pointer based connections, you can even connect to functions which are not explicitely declared Q_SLOT ... and you see right away whether your connection will work or not.

Btw: QObject::connect(....) has a return value, that you can check or output with qDebug() for example.

[ademmler]

@JonB

thx for teaching me this - its very helpful to see old and new syntax side by side.

However I try to use eventFilter instead. As you can see from my post above.
Basically it works, but after a while (some mouse clicks in the UI) the event filter seems to be "vanished" or better to say does not work any longer.
Any idea what's causing this or what I do wrong here?

[JonB]

@ademmler Not other than put in some qDebug()s if you want to know what it is doing.

[ademmler]

@JonB

And I found a bug in my code. Hence the approach of using "installEventFilter" is the right way of doing.

Thx to all!

[Milly]

I achieved something similar by subclassing QComboBox and adding the aboutToShow signal myself. I override the showPopup method so it emits the signal before showing the comboBox options.