title: android-kotlin error : unresolved reference databinding & ActivityMainBinding
body: <p>I am using Android Studio 3.0 Canary 6 version. I've enabled dataBinding in my class and the code doesn't show any error. But, when I build an APK, the build fails and shows the following error:</p>
  
  <pre><code>Error:(8, 37) Unresolved reference: databinding  
  Error:(22, 26) Unresolved reference: ActivityMainBinding  
  Error:(38, 50) Unresolved reference: ActivityMainBinding  
  Error:(43, 52) Unresolved reference: ActivityMainBinding  
  Error:(46, 52) Unresolved reference: ActivityMainBinding  
  Error:(49, 52) Unresolved reference: ActivityMainBinding  
  Error:(52, 52) Unresolved reference: ActivityMainBinding  
  Error:(55, 52) Unresolved reference: ActivityMainBinding  
  Error:(58, 52) Unresolved reference: ActivityMainBinding  
  Error:(61, 52) Unresolved reference: ActivityMainBinding  
  Error:(64, 52) Unresolved reference: ActivityMainBinding  
  Error:(67, 52) Unresolved reference: ActivityMainBinding  
  Error:(70, 52) Unresolved reference: ActivityMainBinding  
  Error:(73, 52) Unresolved reference: ActivityMainBinding  
  Error:Execution failed for task ':app:compileDebugKotlin'.  
  Compilation error. See log for more details
  </code></pre>
  
  <p>The top level build.gradle file is as follows :  </p>
  
  <pre><code>buildscript {
  ext.kotlin_version = '1.1.3-2'
  repositories {
      google()
      jcenter()
  }
  dependencies {
      classpath 'com.android.tools.build:gradle:3.0.0-alpha6'
      classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
  
      // NOTE: Do not place your application dependencies here; they belong
      // in the individual module build.gradle files
  }
  }
  
  allprojects {
      repositories {
          google()
          jcenter()
          mavenCentral()
      }
  }
  
  task clean(type: Delete) {
      delete rootProject.buildDir
  }
  </code></pre>
  
  <p>The module build.gradle file is as follows :  </p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  apply plugin: 'kotlin-android'
  
  apply plugin: 'kotlin-android-extensions'
  
  apply plugin: 'kotlin-kapt'
  
  android {
      compileSdkVersion 26
      buildToolsVersion "26.0.1"
      defaultConfig {
          applicationId "com.example.jimil.calculator"
          minSdkVersion 15
          targetSdkVersion 26
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner 
              "android.support.test.runner.AndroidJUnitRunner"
      }
      buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 
                  'proguard-rules.pro'
          }
      }
      dataBinding{
          enabled =  true
      }
  }
  
  dependencies {
      implementation fileTree(dir: 'libs', include: ['*.jar'])
      androidTestImplementation ('com.android.support.test.espresso:espresso-
          core:3.0.1', {
              exclude group: 'com.android.support', module: 'support-
                  annotations'
      })
      implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
      implementation 'com.android.support:appcompat-v7:26.1.0'
      testImplementation 'junit:junit:4.12'
      implementation 'com.android.support.constraint:constraint-layout:1.0.2'
      kapt 'com.android.databinding:compiler:3.0.0-alpha6'
  }
  
  kapt {
      generateStubs = true
  }
  </code></pre>
  
  <p>The MainActivity.kt class is :  </p>
  
  <pre><code>import com.example.jimil.calculator.databinding.ActivityMainBinding  
  ...  
  class MainActivity : AppCompatActivity() {  
      private var binding: ActivityMainBinding? = null  
      ...  
  }
  </code></pre>
  
  <p>Please help me solve the build error. </p>