Running a script when opening a TDL list? Plus Subtask counting upgrade?

[JonR]

Hi, I have a few simple UDTs set up, handy for doing repetitive tasks.

I also have a 'counter' custom field which aggregates throughout a list - this allows the number of items in a tree of items to be shown. Simply a number field which I populate with '1'.

If i wrote a UDT to populate that field with '1' on all selected tasks... could this then run when the list is opened, so that the counter is always up to date? How can any UDT be run on startup? And how can all items (or a selection) be selected programmatically?

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Extrapolating to a wishlist item - Could such a counter be created as a built-in field option?

The use case is that the Subtasks field does not count below the immediate level under the parent. Put another way, can this field be updated to include ALL the tasks in the tree beneath the parent?
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Thanks!