I am developing a custom widget.

Something like:

instance.web.form.widgets.add('MyWidget', 'instance.mymodule.MyWidget');

instance.mymodule.MyWidget = instance.web.form.AbstractField.extend( {
    template: "MyTemplate",

   //Other definitions...

});

This is working OK. Now I want to define how the cells for a treeview look for this widget.

This is what I've tried:

instance.web.list.columns.add('MyWidget', 'instance.fieldservice.MyColumnList');

instance.fieldservice.MyColumnList = instance.web.list.Column.extend({
        format: function (row_data, options) {
            return 'MyColumn';
        },

    });