Delete A Row From QGridLayout

Question

All, I am maintaining a QGridLayout of QLabels which show the coefficients of a polynomial. I represent my polynomial using QList<double>.

Each time I update my coefficients, I update my labels. When changing the size of the list, my method does not works well. QGridLayout::rowCount() doesn't update correctly. I am wondering if there's a way to remove rows from a QGridLayout.

---

Code follows, updating the QGridLayout size with more (or less) QLabels

int count = coefficients->count(); //coefficients is a QList<double> *
if(count != (m_informational->rowCount() - 1)) //m_information is a QGridLayout
{
    SetFitMethod(0);
    for(int i = 0; i < count; ++i)
    {
        QLabel * new_coeff = new QLabel(this);
        new_coeff->setAlignment(Qt::AlignRight);
        m_informational->addWidget(new_coeff, i+1, 0);
        QLabel * param = new QLabel(this);
        param->setAlignment(Qt::AlignLeft);
        param->setText(QString("<b><i>x</i><sup>%2</sup></b>").arg(count-i-1));
        m_informational->addWidget(param, i+1, 1);
        QSpacerItem * space = new QSpacerItem(0,0,QSizePolicy::Expanding);
        m_informational->addItem(space, i+1, 1);
    }

    m_informational->setColumnStretch(0, 3);
    m_informational->setColumnStretch(1, 1);
    m_informational->setColumnStretch(2, 1);
}

The SetFitMethod (it's an initial mockup)

void SetFitMethod(int method)
{
    ClearInformational();
    switch(method)
    {
    case 0: //Polynomial fit
        QLabel * title = new QLabel(this);
        title->setText("<b> <u> Coefficients </u> </b>");
        title->setAlignment(Qt::AlignHCenter);
        m_informational->addWidget(title,0,0,1,3, Qt::AlignHCenter);
    }
}

The Clearing Method:

void ClearInformational()
{
    while(m_informational->count())
    {
        QLayoutItem * cur_item = m_informational->takeAt(0);
        if(cur_item->widget())
            delete cur_item->widget();
        delete cur_item;
    }
}

Answer 1

The issue is that QGridLayout::rowCount() doesn't actually return the number of rows that you can see, it actually returns the number of rows that QGridLayout has internally allocated for rows of data (yes, this isn't very obvious and isn't documented).

To get around this you can either delete the QGridLayout and recreate it, or if you're convinced that your column count won't change, you can do something like this:

int rowCount = m_informational->count()/m_informational->columnCount();