How to initialize PopupMenu with first element on each dynamic update?

October 18, 2017 BI News and Info

I wrote a function, which lists directories, which may contain “model” files in the following format

{dirpath1->dirname1, dirpath2->dirname2, ...

i.e. in format, suitable for PopupMenu function.

Then I wrote a function, which lists model files in given directory in the same way

{filepath1->filename1, filepath2->filename2, …

I was wishing to select directory in first popup and then select file in second popup and wrote

PopupMenu[Dynamic[dir], GetModelDirectories[]]

Dynamic[PopupMenu[Dynamic[fil], GetMatFiles[dir]]]

It worked, but partially: if I change first popup, second popup turns empty

and I need explicitly select second popup

Is it possible to initialize second popup automatically to the first item in the list?

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