How to get last visible item in QTreeView

Question

I have a QModelIndex of item in QTreeView.

How to test is this item is last visible item in QTreeView?

Fox example:

-item1 // expanded
--sub11
--sub12
-item2 // collapsed
--sub21

Function bool isItemVisible( QModelIndex idx ); should return true for item2, and false for sub21.

Note that rows may have different height.

Answer 1

Well, I have made the following sketch for the possible function that will tell you whether your item is the last one in the tree view hierarchy:

The function itself:

bool isItemVisible(QTreeView *view, const QModelIndex &testItem,
                   const QModelIndex &index)
{
    QAbstractItemModel *model = view->model();
    int rowCount = model->rowCount(index);
    if (rowCount > 0) {
        // Find the last item in this level of hierarchy.
        QModelIndex lastIndex = model->index(rowCount - 1, 0, index);
        if (model->hasChildren(lastIndex) && view->isExpanded(lastIndex)) {
            // There is even deeper hierarchy. Drill down with recursion.
            return isItemVisible(view, testItem, lastIndex);
        } else  {
            // Test the last item in the tree.
            return (lastIndex == testItem);
        }    
    } else {
        return false;
    }    
}

How to use:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QTreeView view;
    MyModel model; // The QAbstractItemModel.
    view->setModel(&model);

    QModelIndex indexToTest = model.index(3, 0); // Top level item (4-th row).
    // Start testing from the top level nodes.
    bool result = isItemVisible(&view, indexToTest, QModelIndex());

    return a.exec();
}

Please note, that I haven't intensively tested this function, but I think it will work fine. You can, of course, improve it.

UPDATE:

After discussing the proposed method, I suggest the following solution that will decrease the number of function calls and improve overall performance.

// Returns the last visible item in the tree view or invalid model index if not found any.
QModelIndex lastVisibleItem(QTreeView *view, const QModelIndex &index = QModelIndex())
{
    QAbstractItemModel *model = view->model();
    int rowCount = model->rowCount(index);
    if (rowCount > 0) {
        // Find the last item in this level of hierarchy.
        QModelIndex lastIndex = model->index(rowCount - 1, 0, index);
        if (model->hasChildren(lastIndex) && view->isExpanded(lastIndex)) {
            // There is even deeper hierarchy. Drill down with recursion.
            return lastVisibleItem(view, lastIndex);
        } else  {
            // Test the last item in the tree.
            return lastIndex;
        }    
    } else {
        return QModelIndex();
    }
}

Define a variable that will keep track of the last visible item in the tree. For example:

static QModelIndex LastItem;

Update the cached item each time the tree view items expanded or added/removed. This can be achieved in the slot that connected to QTreeView's expanded(), collapsed(), :rowsAboutToBeInserted, rowsAboutToBeRemoved() signals, i.e

..
{
    LastItem = lastVisibleItem(tree);
}

Finally, to test a tree view item, just compare its model index with this LastItem without calling search function again.