Android- Cannot resolve symbol BaseObservable

You should add these lines of code to your app level gradle file as written in the 1.2 section

android {
    ....
    dataBinding {
        enabled = true
    }
}

dataBinding {
   enabled = true
}

is deprecated with the newer gradle

Instead:

apply plugin: 'com.android.application'
// if you use kotlin, apply these plugins too
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-kapt'

android {
    ...

    buildFeatures {
        dataBinding  = true
    }

    ...
}