ClassNotFoundException: Didn't find class "android.databinding.DataBinderMapper"

Make sure that ALL your modules that use DataBinding have it enabled. This was the reason I got that exception.

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

finally i was able to solve this issue. It seems there was a conflict between apt version of the app and library modules.

upgraded the apt version in the app to

classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'

Besides adding the following to build.gradle:

android {
    dataBinding {
        enabled = true
    }
}

I also have to add the following dependency:

dependencies {
    kapt 'com.android.databinding:compiler:3.0.1'
}