I'm working on a similiar problem developing my chat and I was checking on how whatsapp solves it to get an idea to work on it.
On mobile and inside a conversation, when your keyboard is up on the screen and you click on attachments, the attachments window overrides the keboard like the image below. It also look likes the activity under it freezes ( you can look at the slash "|" on the EditText, it seems that is freeze ).
I was wondering how WP could override the keyboard and why it looks like the activity under it is freezing, thanks in advance!
