title: Why is QListView blank after setRootIndex?
body: <p>I have a tree like model (which iff non-empty has always height 2). In a tree view, the data is correctly displayed. However, I want to display the data in two ListViews, <code>dupFilesOverview</code> and <code>dupFilesDetailview</code>:
  <code>dupFilesOverview</code> is showing the elements at depth 1, while <code>dupFileDetailView</code> should show the children of the of the element selected  in the overview.</p>
  
  <p>To do this, I'm currently using the following code (where dm is my model):</p>
  
  <pre><code>ui.dupFilesOverview-&gt;setModel(&amp;dm);
  ui.dupFilesDetailview-&gt;setModel(&amp;dm)
  QObject::connect(ui.dupFilesOverview-&gt;selectionModel(), &amp;QItemSelectionModel::selectionChanged, [&amp;ui, &amp;dm](const QItemSelection&amp; selection) {
     QModelIndex index  =selection.indexes().first();
     ui.dupFilesDetailview-&gt;setRootIndex(index);
  });
  </code></pre>
  
  <p>Via some qDebug output,</p>
  
  <pre><code>qDebug() &lt;&lt; index &lt;&lt; dm.data(index, Qt::DisplayRole) &lt;&lt; dm.hasChildren(index) &lt;&lt; dm.data(index.child(1,0), Qt::DisplayRole);
  </code></pre>
  
  <p>I  verified that the index I've obtained is indeed the one that I want: It is valid and has the expected children. From the documentation, I would expect <code>dupFilesDetailDetailview</code> to now show the children of my model at the specified index.  Alas, it stays blank instead. Is there anything that I'm missing?</p>