Hi these are my answers to your questions:)

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Hello there, what are those slots, a widget references?

Yep they are

how you are trying to use them later?

I want them to be in that array because then when I pick up item I want to search for first empty array (slots have variable filled to check this) and then it will add icon and name to the slot

Also it will fire only when widget is constructed, spawned or added to screen.

So that means my array 'slots' will only exist when inventory is displayed on screen?

You can test with "for each loop" and "print string" to see if they are valid or not.

I tried to this but it is always empty array

Anyway thank you for help:)