I learned after about an hour of puzzlement tonight that the parameters for XUL’s nsITreeView::getCellText() have changed. Formerly, you passed a numeric id corresponding to the row in a tree as the first parameter and a string matching the id attribute of the desired column as the second. This provokes errors in recent versions of Gecko because the function now expects an nsITreeColumn as the second parameter.

A couple of nice people (db48x and gavin) on #developers at irc.mozilla.org pointed me to some docs that helped me unpuzzle myself. First, the idl file for nsITreeview, which clued me in to the fact that the second parameter is no longer a string. Second, a link to a mailing list posting about the change.

Basically, the change was implemented in order to do away with the necessity to give treecols an id. By generalizing the function a bit to expect an nsITreeColumn, Gecko can now figure out which column to use in a number of ways. For example:

tree.columns.getColumnFor(treeColElement);
tree.columns.getNamedColumn(treeColID);
tree.columns.getColumnAt(index);

In my recent case, I knew the column name, so I passed tree.columns.getNamedColumn(‘identifier’) rather than just ‘identifier’ to the getCellText() function and it worked like a charm.

I post this pretty much for my own later reference.