Android Studio 3.0 Unsigned Apk Not Installing

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.

File-> Invalidate Caches/restart

solve problem for me.

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...

In the latest version of Android Studio (4.1.1) just rebuild the project. (Build>Rebuild Project). Then get you apk at AndroidStudioProjects<Project Name>\app\build\outputs\apk\debug.

Hope it'll work!

first clean your project. delete old apk and json file in debug folder. then re generate build apk. it works.