I've been using AS for months, but since two days I get an error when I try to run my app:
Unable to run 'adb': null
'C:\Users\lapof\AppData\Local\Android\Sdk\platform-tools\adb.exe start-server' failed -- run manually if necessary
* daemon not running; starting now at tcp:5037
could not read ok from ADB Server
* failed to start daemon
error: cannot connect to daemon
I've read about a lot of people having this problem, but the solutions provided don't work for me. I read these questions in particular:
A lot of answers to these questions say to close adb.exe from task manager, the problem is that adb.exe is not running and if I try to restart it by typing .\adb start-server on a PowerShell window I get the same error.
I also try to restart my PC but it didn't work. On the Android device I'm trying to connect to (Samsung Galaxy S8) I enabled USB debugging. I even tried to eliminate all the authorized devices, but nothing worked.
I checked if the 5037 port was used by other processes, but it is used by adb.exe (and the firewall state on that port is allowed and not limited). By the way, as I said, in the task manager adb.exe is not present.
Last I tried to follow the instructions provided in the last question I linked (basically I re-downloaded adb.exe).
Initially I ran .\adb start-server and this strange error occurs:
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
** daemon still not running
error: cannot connect to daemon
and then when I try to run my app on Android Studio it occurs this new error when it tries to start adb:
Unable to run 'adb': null
'C:\Users\lapof\AppData\Local\Android\Sdk\platform-tools\adb.exe start-server' failed -- run manually if necessary
ADB server didn't ACK
* failed to start daemon *
and then if I try to .\adb kill-server and then .\adb start-server or .\adb devices or .\adb usb the same error occurs again.
Moreover when I connect my device now it asks me to authorize my PC to connect.
I don't know if this can help, but lately I deactivated a lot of Windows services (but I don't think I deactivated something related to Android Studio).
I solved the problem on my own.
Out of frustration I opened Control Panel > System and security > Windows defender firewall > Allowed applications and I added adb.exe (both private and public networks).
I came back to Android Studio, ran the app and magically it managed to initialize ADB and my phone connected via USB was there.
I don't really know why this worked, since when I checked in Start > All Programs > Accessories > System Tools > Resource Monitor > Network > Listening Port it said that on port 5037 the firewall was allowed.
Moreover I don't know why up to a week ago all worked fine and now I had to do this process to make it work.
If someone more experienced manages to explain this behaviour better I'll update this answer (or accepts his as best answer)