So create alist view of entity A.in the list view u have this button.
on this button.do a show page
the target page need to have a data view of entitiy A and data source set as page parameter and it will work.
in case it doesnt please put a comment
First, you want to check the Entity is the same for the list view and data view of the popup, Make sure that you mapped the correct attribute in the data view.
Because the button is not in your list view, I believe the object that gets passed to your button is the wrong one. Even if you select an option in the list the and then click on the button. The object you selected is not the one getting passed to the button.
Thus you will have to include your button in the list view or set your double click action to opening the popup page for the listview.
Other options will be a bit more complicated.