Does QML TreeView support signal layoutChanged emitted from model?

Question

I have a model that works well with QTreeView. In the model I implemented a sort that looks like this:

void SimpleTreeModel::sort(Node* sortedNode)
{
     emit layoutAboutToBeChanged(QList<QPersistentModelIndex>(), VerticalSortHint);
     QModelIndexList oldIndices = persistentIndexList();

     Node::SortType sortType = Node::Down;

     //sort starting node
     sortedNode->sortChildren(sortType);

     QModelIndexList newIndices;
     newIndices.reserve(oldIndices.size());
     for(const auto &i : oldIndices)
     {
         Node* node = const_cast<Node*>(nodeFromIndex(i));
         QModelIndex index = indexFromNode(node);
         newIndices.push_back(index);
     }
     changePersistentIndexList(oldIndices, newIndices);

     QModelIndex startingIndex = indexFromNode(sortedNode);
     emit layoutChanged({ QPersistentModelIndex(startingIndex) }, VerticalSortHint);
}

when I call this function, QTreeView updates the view, but TreeView in QML don't do this. QML TreeView usage:

TreeView
{
    model: treeModel
    TableViewColumn 
    {
        title: "Title"
        role: "title"
        width: 700
    }
}

What am I doing wrong? Why the view does not update the layout of the elements after sorting?

Pavan Chandaka Pavan Chandaka · Accepted Answer · 2017-10-20T20:27:46

I think you need to delegate the tree view item. Data is provided to delegate.

Try changing your QML TreeView as shown below by adding itemDelegate

TreeView
{
    model: treeModel

    itemDelegate: Item {
       Text {
               color: styleData.textColor
               text: styleData.value
            }
    }

    TableViewColumn 
    {
        title: "Title"
        role: "title"
        width: 700
    }
}

Look into below link to understand the importance of delegate, between model and QML view. There is an image which easily explains.

http://doc.qt.io/qt-5/qtquick-modelviewsdata-modelview.html

Delegate - dictates how the data should appear in the view. The delegate takes each data in the model and encapsulates it. The data is accessible through the delegate.

Does QML TreeView support signal layoutChanged emitted from model?

1 Answers