cannot resolve symbol 'AuthUI' in version 4.0.1

I've followed the introduction of Firebase, but it seems there is something wrong with my build.gradle.

Code of MainActivity

public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if (user !=null){
                // user is signed in
            }else {
                //user is signed out
                startActivityForResult(
                        AuthUI.getInstance()
                                .createSignInIntentBuilder()
                                .setAvailableProviders(Arrays.asList(
                                        new AuthUI.IdpConfig.GoogleBuilder().build(),
                                        new AuthUI.IdpConfig.FacebookBuilder().build(),
                                        new AuthUI.IdpConfig.TwitterBuilder().build(),
                                        new AuthUI.IdpConfig.GitHubBuilder().build(),
                                        new AuthUI.IdpConfig.EmailBuilder().build(),
                                        new AuthUI.IdpConfig.PhoneBuilder().build()))
                                .build(),
                        RC_SIGN_IN);
            }
        }

Code of Build.gradle

dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'

compile 'com.android.support:design:26.0.+'
//24.2.0
compile 'com.android.support:appcompat-v7:26.0.+'
//v7:24.2.+

// Displaying images
compile 'com.github.bumptech.glide:glide:3.6.1'


//FireBase Dependency
android {
compileSdkVersion 26
buildToolsVersion "27.0.3"
// 27.0.3
defaultConfig {
    applicationId "com.google.firebase.udacity.friendlychat"
    minSdkVersion 16
    targetSdkVersion 24
    versionCode 1
    versionName "1.0"

}
defaultConfig {
    // ...
    resConfigs "en" // And any other languages you support
}
implementation 'com.google.firebase:firebase-core:16.0.1'
compile 'com.google.firebase:firebase-database:16.0.1'
compile 'com.google.firebase:firebase-auth:16.0.1'
compile 'com.google.android.gms:play-services-auth:15.0.1'
compile 'com.google.firebase:firebase-firestore:17.0.1'
compile 'com.google.firebase:firebase-storage:16.0.1'
implementation 'com.firebaseui:firebase-ui-auth:4.1.0'
}

I've invalidated cache and restart for several times but it seems didn't help. Are there some other dependencies I've missed?