This is a general post that might help someone in the future. I've struggled with this issue twice. Once for dropdowns, and once for galleries. It may not be the accepted or correct way to fix this issue, but since it worked it might save you a few hours of pain.
Dropdowns and galleries work fine with collections as data sources in the web player where I do my development. In both cases, the collections are built on the fly prior to displaying the dropdown or gallery. When it comes to using a named collection as the data source in either of those types of controls in the android player, the controls refuse to populate.
I went through all the testing steps, verifying that that was present before the controls became visible. Both by displaying a count, and then the data from the first record in the collection in a label.
I discovered my solution quite by accident. At my wits end, I assigned the collection to a variable and then used the variable as the data source in the control in question. It worked in both case.
Set(variable name, collection name);
Then in the items property:
variable name
