Checkbox in a header cell in QTableView

Question

I want to have a simple column header with a checkbox that selects/ deselects all rows in a QTableView. Clicking the check box in the header causes either to select or desel

Answer 1

I am surprised such a hacky solution is recommend and used.

First: The check state should be stored in the model. All the tools are already there.

bool MyModel::setHeaderData(int index, Qt::Orientation orient, const QVariant& val, int role)
{
  if(Qt::Vertical != orient)
    return Base::setHeaderData(index, orient, val, role);

  storeCheckState(index, val);
  emit headerDataChanged(orient, index, index);
  return true;
}

QVariant MyModel::headerData(int index, Qt::Orientation o, int role) const
{
    if(Qt::Vertical != orient)
      return Base::headerData(index, o, role);

    switch(role)
    {
    ...
    case Qt::CheckStateRole:
      return fetchCheckState(index);
    }

  return Base::headerData(index, o, role);
}

Second: We toggle checked state simply by handling the click signal on the header.

connect(header, &QHeaderView::sectionClicked, receiver
        , [receiver](int sec)
{
  const auto index = logicalIndex(sec);
  model()->setHeaderData(index
                         , Qt::Vertical
                         , Qt::CheckState(model()->headerData(index, Qt::Vertical, Qt::CheckStateRole).toUInt()) != Qt::Checked ? Qt::Checked : Qt::Unchecked
                         , Qt::CheckStateRole);
});

Third: At this point we have fully functional checking behavior, only part missing is the visualization. The smartest way to go is to again use the model, taking advantage of the Qt::DecorationRole. Here is a dummy implementation:

QVariant MyModel::headerData(int index, Qt::Orientation o, int role) const
{
    if(Qt::Vertical != orient)
      return Base::headerData(index, o, role);

    switch(role)
    {
      case Qt::DecorationRole:
      {
        QPixmap p{12,12};
        p.fill(Qt::CheckState(headerData(index, o, Qt::CheckStateRole).toUInt()) ? Qt::green : Qt::red);
        return p;
       }
       break;
    ...
    }

  return Base::headerData(index, o, role);
}

Of course, one can draw a real checkbox there using the styled drawing.

Notice, this solution does not require sub-classing and custom widgets.

Also, the check state is decoupled from the view/UI. The only downside is fact the visuals are handled by the model, but this is optional - any way can be used to draw the check state, the one from the alternative answers included.