jQuery Grid Plugin - jqGrid

I have a select column which works fine.  However I need to freeze the value if the user tries to edit the record.  My strategy is to use a custom field type and determine what mode the edit form is in, i.e. if we are 'new' (add) then display a selector else if editing a current record, display a readonly text box.

So the question is, how do I determine what edit mode we are in?  I tried getGridParam('selrow'); but that returns the currently selected row irrespective of if we are in add or edit.

Any help on this would be appreciated.

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