Unresolved reference: kotlinx

Add kotlin-android-extensions in our buildscript’s dependencies:

1. In your project-level build.gradle

buildscript {
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"
    }
}

and apply the kotlin-android-extensions plugin:

2. In your module-level build.gradle

apply plugin: 'kotlin-android-extensions'