public static interface TreeView.RowExpanded

Emitted when a row in the TreeView has been expanded, i.e. when its child nodes are shown. A row is expanded either by clicking in the little arrow near it, or by pressing the + key when a row is selected. Of course, a row can be only expanded when it has child rows, and so it can be only emitted when the TreeView is used with a hierarchical model such as TreeStore.

In general, you've got the TreeModel and especially its DataColumns visible, so to use TreeView.RowExpanded you can just:

 final TreeModel model;
 final DataColumnString column;
 
 view.connect(new TreeView.RowExpanded() {
     public void onRowExpanded(TreeView source, TreeIter iter, TreePath path) {
         ... = model.getValue(iter, column);
     }
 });
 

Remember that TreeIters and TreePaths are not stable over changes to the model, so get on with using path right away.