Over the course of this chapter, we will make use of a number of external application dependencies. As such, it is important we include them in the project now. Open your module-level build.gradle file and add the following dependencies to it:

dependencies {
  implementation fileTree(dir: 'libs', include: ['*.jar'])
  implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7
                  :$kotlin_version"
  implementation 'com.android.support:appcompat-v7:26.1.0'
  implementation 'com.android.support.constraint:constraint-layout:1.0.2'
  implementation 'com.android.support:recyclerview-v7:26.1.0'
  implementation 'com.android.support:design:26.1.0'

  implementation "android.arch.persistence.room:runtime:1.0.0-alpha9-1"
  implementation "android.arch.persistence.room:rxjava2:1.0.0-alpha9-1"
  implementation 'com.android.support:support-v4:26.1.0'
  implementation 'com.android.support:support-vector-drawable:26.1.0'
  annotationProcessor "android.arch.persistence.room:compiler
                       :1.0.0-alpha9-1"

  implementation "com.squareup.retrofit2:retrofit:2.3.0"
  implementation "com.squareup.retrofit2:adapter-rxjava2:2.3.0"
  implementation "com.squareup.retrofit2:converter-gson:2.3.0"
  implementation "io.reactivex.rxjava2:rxandroid:2.0.1"

  implementation 'com.github.stfalcon:chatkit:0.2.2'

  testImplementation 'junit:junit:4.12'
  androidTestImplementation 'com.android.support.test:runner:1.0.1'
  androidTestImplementation 'com.android.support.test.espresso
                             :espresso-core:3.0.1'
}

Ensure that no conflicting Android support library versions exist in the build.gradle file. Now modify the build.gradle project file to include the jcenter and Google repositories as well as the Android build tools dependency:

Top-level build file where you can add configuration options common to all sub-projects/modules:

buildscript {
  ext.kotlin_version = '1.1.4-3'
  repositories {
    google()
    jcenter()
  }
  dependencies {
    classpath 'com.android.tools.build:gradle:3.0.0-alpha9'
    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
  }
}

allprojects {
  repositories {
    google()
    jcenter()
  }
}

task clean(type: Delete) {
  delete rootProject.buildDir
}

Don't worry, about what the dependencies added for now, all will be revealed over the course of this chapter.