This week an Android update for the Microsoft Flow app showed that the team has been working on extra inputs for Flow Buttons. The input types they added this week are File and Email inputs.
Really cool to see the Microsoft Flow team move in this direction, because there are loads of scenarios possible with these extra inputs.
When using the file input, you won't get the file name as an output from the "Manually trigger a flow" trigger. It is easy to get the file name with the compose action. Add the compose action and open the expression panel. Scroll down to the conversion functions and select the "string(value)" function. Switch to the dynamic content panel and select the file content output from the "Manually trigger a flow" trigger outputs. You will see this function in your compose action:
As you can see it's looking for the contentBytes value in the file input. We don't want that for the file name, so if you change contentBytes into name it will output the file name for you. The following function is the right one for the file name:
When you click 'OK' in the expression panel Flow will add this to your compose action. You can use the output value where-ever you want to use the file name.
NOTE: The Flow Team told me they have it on their backlog to add the file content name to the standard outputs, but they don't have a date for this... So let's vote this up on their ideas forum.