I would like to confirm a few things with you:
- Do you want to get the list GUID and then put it in a column in the current list? The GUID of a list is a fixed value and will not change once the list is created. Why can’t we just set the GUID as the default value of the column?
- Do you want to auto-fill this column in only one list or multiple lists in your site?
- Can you explain a bit more about the following lines:
The new item page appears in a pop up (have the pop up dialog turned on - this keeps the ID in the URL otherwise we lose it because we go to a new item aspx page)
Do you mean the “Launch forms in a dialog” feature? Per my test, list GUID appears in the address bar only when we try to manage the list via List Settings. It will not show in the URL when we create new items.
Please provide detailed information about your requirement. Feel free to point it out if I have misunderstood your situation.