今天开始了一个新项目，目标是使用androidx库的API 28。在我的项目中尝试使用Retrofit或OkHTTP 3时，gradle sync运行正常，但当尝试在设备上运行时，Kotlin编译器会抱怨“Unresolved reference to retrofit 2/okhttp”。
build.gradle

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

//apply plugin: 'kotlin-kapt'

android {
    compileSdkVersion 'android-P'
    defaultConfig {
        applicationId "com.opticalgenesis.lbp.ktlab"
        minSdkVersion 21
        targetSdkVersion "P"
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.0.0-alpha1'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.0'
    implementation 'androidx.browser:browser:1.0.0-alpha1'
    implementation 'com.google.android.material:material:1.0.0-alpha1'
    implementation 'androidx.core:core-ktx:1.0.0-alpha1'
    implementation 'com.android.volley:volley:1.1.0'
    implementation 'com.squareup.retrofit2:retrofit:2.4.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.4.0'
    implementation 'com.squareup.okhttp3:okhttp:3.10.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.1.0-alpha3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0-alpha3'
}

相关的Kotlin代码

import android.content.Context
import android.content.Intent
import android.net.Uri
import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity

import retrofit2.Call
import retrofit2.Callback
import retrofit2.Retrofit
import retrofit2.Response
import retrofit2.converter.gson.GsonConverterFactory

class LoginConfirmActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val i = intent
        val data = i.data

        val u = Uri.parse(data.toString())
        val code = u.getQueryParameter("code")
        val state = u.getQueryParameter("state")

        val generatedState = getSharedPreferences(MainActivity.PREFS_KEY, Context.MODE_PRIVATE).getString(MainActivity.STATE_KEY, "")

        if (state == generatedState) {
            Log.d("OAUTH", code)
            val r = Retrofit.Builder().apply {
                baseUrl("https://gitlab.com/oauth")
                addConverterFactory(GsonConverterFactory.create())
            }.build()
            val authApi = r.create(GitLabAuthApi::class.java)
            val codeResponse = authApi.getAccessToken(
                    Keys.appId,
                    Keys.secret,
                    code,
                    "authorization_code",
                    Keys.redirectUri)
            codeResponse.enqueue(object : Callback<CodeResponse> {
                override fun onResponse(call: Call<CodeResponse>?, response: Response<CodeResponse>) {
                    if (response.isSuccessful) {
                        parseAndStoreCodeResults(response.body()!!)
                    } else {
                        Log.e("AUTH_TAG", "Attempt to get code resulted in error ${response.errorBody()}")
                    }
                }

                override fun onFailure(call: Call<CodeResponse>?, t: Throwable?) {
                    t?.printStackTrace()
                }
            })
        } else {
            Log.e("AUTH_TAG", "States don't match.")
        }
    }
}

错误消息x1c 0d1x
任何帮助都很感激。