The easiest way to build an Android app from the command line on Ubuntu.
First run (cd android_tools; make install)
This will install a binary package with the sdkmanager, then use the sdkmanager to install remaining Android tools and an Android SDK and platform.jar for android-30.
Then run make
to build the build/app.apk
Then run make install_phone
to send the apk to your USB connected android phone.
You can easily build against android-29 instead.
First run (cd android_tools; make install_29)
to get platform 29.
Then run: make BUILD=build29 ANDROID_VERSION=android-29
This will generate build29/app.apk