About six months ago I wrote a blog post about this subject on Medium.com site https://medium.com/@kcraigo/powerapps-maintaining-state-5dccbebe7ac6, (This post is no longer available as of Jan/2019) this post has an embedded video which demoed the final outcome of the post, https://www.youtube.com/watch?v=2UZ7B-5Qs78
My apologies, this caused some confusion for Youtube viewers who did not read the blog post but instead went directly to the video. There is no sound and it is only around 42 seconds long with no explanation.
So I recorded this follow up video with audio and a complete walk through.
Hope this helps!
I just posted a new Tutorial : https://webdevbythebay.com/powerapps-state/ using 2 Gallery Controls and Collections.
