Unresolved reference: BR (Android Studio)

Issue

My top level build.gradle:

buildscript {
    ext.kotlin_version = '1.2.41'
    ext.lifecycle_version = "1.1.1"
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.1.3'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

My project level build.gradle:

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

dependencies {
    ...
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    implementation "android.arch.lifecycle:extensions:$lifecycle_version"
}

I also added android.databinding.enableV2=true to gradle.properties per Google documents (https://developer.android.com/topic/libraries/data-binding/start)

When I try to run, it shows Unresolved reference: BR error in my BaseViewHolder class. It seems that BR class has been properly generated but it also says duplicate class found in the file .../R.java when I mouse over the class name. What have I done wrong?

fun bind(obj: Any) {
        binding.setVariable(BR.obj, obj)
        binding.executePendingBindings()
}

Solution

After researching quite a bit, turns out there are a couple things to add in order to use data binding library

project build.gradle

buildscript {
    ext {
        compiler_version = '3.1.3'
    }
    dependencies {
        classpath "com.android.tools.build:gradle:$compiler_version"
    }
}

app build.gradle

apply plugin: 'kotlin-kapt'

android {
    dataBinding {
        enabled = true
    }
}

dependencies {
    kapt "com.android.databinding:compiler:$compiler_version"
}

kapt {
    generateStubs = true
}

I started to have some warnings after adding the data binding library, like 3rd-party Gradle plug-ins may be the cause and Classpath entry points to a non-existent location. But compiles and runs fine

Answered By - Jack Guo