An easier route is to bypass the app and just set up a HTTP page to display whatever sensor value you need to display. For example, the change script_url page:
https://github.com/OpenSprinkler/OpenSprinkler-Firmware/blob/master/server.cpp#L1128
or ap_udpate page:
https://github.com/OpenSprinkler/OpenSprinkler-Firmware/blob/master/server.cpp#L1916
are both done this way. The downside is that it’s not hooked up to the mobile app, but like in the above examples you can access these pages by directly typing in:
http://x.x.x.x/su
or http://x.x.x.x/update
this only requires changes on the firmware side.