Create class by inheriting from QTreeView - qt

Question

I am starting a project using Qt. I am trying two approaches to get a View to do some of the following. This question involves the approach of inheriting from QTreeView.
I like what QTreeView does. I just want some added features.
First, what I want is to make a hierarchy tree view that will allow me to see categories containing other categories, the further right the columns go the more specific they are until it gets to the most specific. The metrics are shown on the row containing the most specific column. The view rows containing each generalized column will be bold and contain a summary of each metric, calculated by the model (or view?). The metrics will be in the model on each row in terms of the most specific column.
For example, consider a model with the following data (the last 3 columns containing numbers):
Country|Province-State|County-Parish|City-Town|Population|PerCapitaIncome|WalMarts
So my view would look similar to this:
Country Province-State County-Parish City-Town Population PerCapitaIncome Walmarts
+ USA 250000000 42000 2354
+ Alabama 9000000 23000 153
+ Barbour 15324 19032 1
Eufaula 6520 23000 1
+ Tennessee 14000000 29000 299
+ Hamilton 70000 41000 4
East Ridge 23000 32000 2
Second, I need it to work with QSqlTableModel. I have seen it show the model before, but it doesn't have any way to create the rows by a heirarchy, similar to above. That was going to be my second modification.
The third reason is bold headers are only an option if you have the sort turned on via:
view->setSortingEnabled(true);
When sort is on, the bold headers only works for the higher-up rows and then turns off on lower ones. I want to fix that bug.
The QTreeView::drawRow virtual method looks to be all I need to override to accomplish the first challenge (and perhaps the third). The second challenge dealing with QSqlTableModel, I'm not so sure about.
Anyhow, I built a simple class inheriting from QTreeView with a generic ctor and dtor that just calls the QTreeView methods. As for drawRow, however, I ran into the following problem. The QTreeView::drawRow function starts out like this:
QTreeView::drawRow(
QPainter *painter,
const QStyleOptionViewItem &option,
const QModelIndex &index) const {
Q_D(const QTreeView);
QStyleOptionViewItemV4 opt = option;
const QPoint offset = d->scrollDelayOffset;
const int y = option.rect.y() + offset.y();
const QModelIndex parent = index.parent();
const QHeaderView *header = d->header;
const QModelIndex current = currentIndex();
const QModelIndex hover = d->hover;
const bool reverse = isRightToLeft();
const QStyle::State state = opt.state;
const bool spanning = d->spanning;
const int left = (spanning ? header->visualIndex(0) : d->leftAndRight.first);
const int right = (spanning ? header->visualIndex(0) : d->leftAndRight.second);
...
The function relies on have Q_D(const QTreeView) run succesfully and return "d", an instance of the QTreeViewPrivate class which contains important info related to layout and the remainder of the function. Since I am inheriting into my CustomTreeView class, CustomTreeViewPrivate will have to be defined and instantiated first if I am to run Q_D(const QTreeView) in CustomTreeView::drawRow().
Is creating this private class really necessary to inherit and make significant changes? What is the benefit of inheriting here if all I can do is some perfunctory processes and then call the QTreeView::drawRow to do the actual drawing?
I want to change how its drawing.

Answer 1

I will try to cover as much of your question as possible. The big thing throughout all of your problems is that much of what you are trying to accomplish should be done through the model, not the view (such as having certain entries in bold). Because of this, you will have to make your own model. You can inherit a QSqlTableModel and alter things as you wish. For example, if you want to bold certain items, in the data model, you could write
QVariant MyModel::data(const QModelIndex & index, int role) const
{
QVariant result = QSqlTableModel::data(index, role);
// add your own qualifications to the following if statement, checking the row
// and such
if(role == Qt::FontRole) {
QFont font = result.value<QFont>();
font.setBold(true);
return font;
}
return result;
}
The last thing you wrote was about Q_D. This is only for use in the Qt source code. If you are implementing your own paint function, you do not have to use this macro.
I would read up on models very heavily, you may need a lot of the stuff in the documentation.