Problem getting QComboBox from QWidget

darkp03

Hi, thanks for your answer.
Im getting closer, but it still wont work. Probably not casting the right way (even though I made it exactly as internet example)

This is what Im doing

QWidget *Widget=ui->tableWidget_DataTs->cellWidget(1,2);
QComboBox *DataRate;
DataRate= qobject_cast<QComboBox*>(Widget);

According to the debugger, Right after I do

QComboBox *DataRate;

DataRate is type QComboBox

After i do

DataRate= qobject_cast<QComboBox*>(Widget);

DataRates transforms into type QComboBox* with a NULL value.

What am I missing?

The casts ive tried.
qobject_cast Obtains a QComboBox* with NULL value
dynamic_cast Obtains a QComboBox* with NULL value
static_cast Obtains a QWidget with information on it
reinterpret_cast Obtains a QWidget with information on it

None of those casts would work

SGaist

Did you check what cellWidget(1, 2) returns ? Is it a valid widget ? What should that be ? How did you put the combo box there in the first place ?

darkp03

Yes, it returns a valid Widget.

This is how I place the ComboBox

QComboBox *Index;
Index=new QComboBox;
QStringList Names;
Names<<"64kbps"<<"32kbps"<<"16kbps";
Index->addItems(Names);
//Here I have created the QComboBox, now I place it in a Widget, and I allign it to the center

QWidget *Widget=new QWidget;
QHBoxLayout *Layout=new QHBoxLayout(Widget);
Layout->addWidget(Index);
Layout->setAlignment(Qt::AlignCenter);
Widget->setLayout(Layout)

ui->tableWidget_DataTs->setCellWidget(0,2,Widget);

SGaist

So cellWidget doesn't return a combo box, it returns a widget containing a layout containing your combo box

maratk1n

@SGaist so, how we can cast it to QComboBox*?

jsulm

@maratk1n Use http://doc.qt.io/qt-5/qobject.html#children to get children widgets of ui->tableWidget_DataTs->cellWidget(1,2); and go through the children list until you can successfully cast to QComboBox*.

maratk1n

@jsulm Thank you! This helped solve my problem.

Create table:

for(int i = 0; i < dataCount; i++){
    ui->tableWidget->horizontalHeader()->setSectionResizeMode(i, QHeaderView::Stretch);
    for (int j = 1; j < rowCount; j++) {
        QWidget *checkBoxWidget = new QWidget();
        QCheckBox *checkBox = new QCheckBox();
        QHBoxLayout *layoutCheckBox = new QHBoxLayout(checkBoxWidget);
        checkBox->setChecked(false);
        layoutCheckBox->addWidget(checkBox);
        layoutCheckBox->setAlignment(Qt::AlignCenter);
        layoutCheckBox->setContentsMargins(0,0,0,0);
        ui->tableWidget->setCellWidget(j, i, checkBoxWidget);
    }
    QComboBox* comboBox = new QComboBox();
    comboBox->setEnabled(false);
    comboBox->addItems(dataTypes);
    ui->tableWidget->setCellWidget(0, i, comboBox);
}

Read checkboxes:

for (int i = 0; i < ui->dataCount->currentIndex(); i++) {
    QComboBox *dataType = static_cast<QComboBox*>(ui->tableWidget->cellWidget(0, i));
    QCheckBox *inversion = static_cast<QCheckBox*>(ui->tableWidget->cellWidget(1, i)->children().last());
    QCheckBox *plot = static_cast<QCheckBox*>(ui->tableWidget->cellWidget(2, i)->children().last());
    QCheckBox *bitwise = static_cast<QCheckBox*>(ui->tableWidget->cellWidget(3, i)->children().last());
    device->setRDataType(str2QVariant(dataType->currentText()), inversion->isChecked());
    if (plot->isChecked()) { // plot needed
    }
    if (bitwise->isChecked()) { // bit representation needed
    }
}

jsulm

@maratk1n One note: you should ALWAYS check pointers! Else your app will crash if any of them is null or dangling pointer.

QComboBox *dataType = static_cast<QComboBox*>(ui->tableWidget->cellWidget(0, i));
...
if (plot && plot->isChecked()) {

maratk1n

@jsulm sure, you are right :)
With dynamic_cast I should try catch exception bad_cast with references or check pointer as well as with static_cast.

JonB

@maratk1n

With dynamic_cast I should try catch exception bad_cast

? dynamic_cast<> returns nullptr if not of right type, it does not throw?

maratk1n

@JonB

Perhaps I incorrectly expressed my thought, but I wanted to say this:

Otherwise, the runtime check fails. If the dynamic_cast is used on pointers, the null pointer value of type new_type is returned. If it was used on references, the exception std::bad_cast is thrown.

SGaist

Beware: static_cast doesn't do any checks so unless it was given a null pointer, it will not return a nullptr.