QTreeView does not show data

[Stephan Lorenzen]

Dear Forum,

I am trying to redo the QTreeView minimal example described in
https://doc.qt.io/qt-5/qtwidgets-itemviews-simpletreemodel-example.html

Basically, all my code is from that side. However, the TreeView is empty and shows no data at all:

What am i doing wrong?

MainWindow::MainWindow() :
	QMainWindow(),
	treeView(new QTreeView(this)),
	treeModel(nullptr)
{
	setCentralWidget(treeView);

	// initialize items with parent and row number
	TreeItem *rootItem = new TreeItem(nullptr, -1);
	TreeItem *item_0   = new TreeItem(rootItem, 0);
	TreeItem *item_1   = new TreeItem(rootItem, 1);
	TreeItem *item_0_0 = new TreeItem(item_0,   0);
	TreeItem *item_0_1 = new TreeItem(item_0,   1);

	// add children to parenta
	rootItem->child.push_back(item_0);
	rootItem->child.push_back(item_1);
	item_0  ->child.push_back(item_0_0);
	item_0  ->child.push_back(item_0_1);

	treeModel = new TreeModel(rootItem);

	treeView->setModel(treeModel);
}

QModelIndex TreeModel::index(int rowNr, int column, const QModelIndex& parent) const
{
	if (!hasIndex(rowNr, column, parent)) return QModelIndex();
	const TreeItem *parentTI;
	if (!parent.isValid()) parentTI = rootItem;
	else parentTI = static_cast<TreeItem*>(parent.internalPointer());
	TreeItem *ti = parentTI->child[rowNr];
	return (createIndex(rowNr, column, ti));
}



QModelIndex TreeModel::parent(const QModelIndex& child) const
{
	if (!child.isValid()) return QModelIndex();
	TreeItem *childItem = static_cast<TreeItem*>(child.internalPointer());
	TreeItem *parentItem = childItem->parent;
	if (parentItem == rootItem) return QModelIndex();
	return(createIndex(parentItem->row, 0, parentItem));
}

int TreeModel::rowCount(const QModelIndex &parent) const
{
	const TreeItem *parentTI;
	if (!parent.isValid()) parentTI = rootItem;
	else parentTI = static_cast<TreeItem*>(parent.internalPointer());
	return (parentTI->child.size());
}

int TreeModel::columnCount(const QModelIndex &) const {return (2);}

QVariant TreeModel::data(const QModelIndex &index, int) const
{
	return(QVariant(QString::fromStdString("TEST")));
}

Best

Stephan

[Christian Ehrlicher]

@Stephan-Lorenzen said in QTreeView does not show data:

QVariant TreeModel::data(const QModelIndex &index, int) const
{
return(QVariant(QString::fromStdString("TEST")));
}

This is wrong - you should only return something for Qt::DisplayRole.

btw: Why convert a plain char string to a std::string just to convert it to a QString? QString can take a plain char* too.

[Stephan Lorenzen]

Wow, you are great -- it works!! Thanks a lot!
Just for curiosity - what exactly goes wrong if data() returns a string for another role? I see things like TooltipRole or StatustipRole, it seems to me that it should not harm if something would be returned for these roles?

[Christian Ehrlicher]

@Stephan-Lorenzen said in QTreeView does not show data:

it seems to me that it should not harm if something would be returned for these roles?

There are also roles like e.g. the font role or color roles. I would guess it's the font role.

[JonB]

@Christian-Ehrlicher
I sort of guessed it might be that too, because QFont contructor takes a string as a "family name". But it says/implies it will pick some other font when it doesn't recognise "TEST"?