Android Studio 3.0 Unsigned Apk Not Installing

Fist Click On Build Icon on android studio after that click Build APK(s) then Generate APK the copy Apk. It is working perfact.

File-> Invalidate Caches/restart

solve problem for me.

Looks like we can not directly use the apk after running on the device from the build->output->apk folder.

After upgrading to android studio 3.0 you need to go to Build -> Build Apk(s) then copy the apk from build -> output -> apk -> debug

Like this -