I am new to android development, and I have been using the command line tools to create an android project. I followed all the instructions given in the tutorial at android
If you are using latest Android Studio, then v7 libraries contradict with AndroidX, only you have to do is:
In Project files go in gradle.properties
Find outandroid.useAndroidX=truethen set it toandroid.useAndroidX=false
Find outandroid.enableJetifier=truethen set it toandroid.enableJetifier=false
Rebuild your project, all will working fine.