Is it possible to reference a parent gallery's item in a nested gallery?

[Steve130]

Hello, I'm trying to use nested galleries to create an expandable menu. Each parent menu has an "expand" button with the following OnSelect formula: 

If(
     CountRows(Filter(Expanded, Value=ThisItem.Object_Identifier)) > 0, 
     Remove(Expanded, First(Filter(Expanded, Value=ThisItem.Object_Identifier))), 
     Collect(Expanded, ThisItem.Object_Identifier)
)

Object_Identifier is a unique identifier for each record in the data source. The expand button adds the current item's identifier to a collection called "Expand".

The child gallery's height property has the following formula:

If(
     CountRows(Filter(Expanded, ????)) > 0, 
     CountRows(Filter('Child Data source', ThisItem.Object_Identifier in ProcessIsUsedToDeliverTheseServices))*32,
     0
)

What I'm trying to do here is: if the parent's item's identifier is in the collection, the height of the child gallery is some positive number. Otherwise its 0 (minimized). However, as you can see I can't figure out a way to reference parent item data, hence the ????. There's no Parent.ThisItem. Is there another way I can do this? Thanks.

[Drrickryp]

@Steve130 

Are you using GroupBy() in the parent gallery?

[Steve130]

No, would that help? If it returns the data table in a different order, I'm not sure how it would help me.

[Drrickryp]

@Steve130 

Most of the applications I have seen have used GroupBy and then have expand and contract the subgallery.  Shane Young has a new video that may help you though.  https://www.youtube.com/watch?v=VNnaymeBN7g