After upgrading to android studio 3.0 the debug apk is saying App not istalled.
The package appears to be corrupted
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 -
Fist Click On Build Icon on android studio after that click Build APK(s) then Generate APK the copy Apk. It is working perfact.
I needed to create a signed APK for it to install correctly.
I have also faced the same problem after upgrading android studio to version 3.0! To solve this issue you need to disable instant run that can be found under File -> Settings -> Build,Execution,Deployment -> Instant Run. Now You need to re-generate a signed apk with both the signature versions enabled i.e V1 & V2 that can be found under Build -> Generate Signed APK Now try to install the signed apk, this time it should be installed perfectly :).
first clean your project. delete old apk and json file in debug folder. then re generate build apk. it works.
So the message "App Not Installed" will refer to multiple causes, and please returning to Android Studio 2.3. from 3.0 is not an option at all!
When we upgrade from Android Studio 2.3 to 3.0 we can find some configuration issues caused mainly by the support libraries, that will cause that our application could not be installed.
To avoid this problem we need to invalidate cache in Android Studio 3.0+ and the problem will be solved.
So File -> invalidate cache and restart
This one is solution that worked for me...
来源：https://stackoverflow.com/questions/47392610/android-studio-3-0-unsigned-apk-not-installing