Display a sentence when you put an attachment

I want to display a condition only if an attachment has been loaded:
I have an attachment embedding area and when the participant inserts their attachment, I want to display a new condition.
I can’t find a way to configure the “hidden” area of the sentence to display.

Maybe this can help:
I have 1 WFG file upload control and 1 label (for the condition message)

In code behind add the following:
Note that this must be under Page_PreRender in order to capture the has file status of the file upload control

J’ai eut le temps de trouver une solution similaire:
Dans la zone “caché” de l’onglet “validation” j’ai inscrit " ! ID_PIECE_JOINTE.HasFile" ce qui fait que quand l’utilisateur met sa pièce jointe, la phrase apparait.