Issue with your examples

I followed your instructions on this side: https://developer.mapquest.com/documentation/android-sdk/

1. Project build.gradle

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

buildscript {

repositories {
google()
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:3.1.2'

// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}

allprojects {
repositories {
google()
jcenter()
maven {
url "https://maven.google.com"
}
maven {
url "http://artifactory.cloud.mapquest.com/artifactory/et-android-binaries"
}
}
}

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

2. Module:app build.gradle

apply plugin: 'com.android.application'

def getApiKey() {
def props = new Properties()
file("mapquest.properties").withInputStream { props.load(it) }
return "\"" + props.getProperty("api_key") + "\""
}

android {
compileSdkVersion 27
defaultConfig {
applicationId "xxxxx"
minSdkVersion 16
targetSdkVersion 27
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
applicationVariants.all { variant ->
variant.buildConfigField "String", "API_KEY", getApiKey() // Provides key for the Navigation SDK
variant.resValue "string", "API_KEY", getApiKey() // Provides key for the MapView used in app layouts
}
}

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.0'
implementation 'com.android.support:design:27.1.1'
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'
implementation('com.mapquest:navigation:3.3.0') // the MapQuest Navigation SDK
implementation('com.mapzen.android:lost:3.0.4') // used for GPS Location Acquisition (see notes)

implementation('com.mapquest:mapping-android-sdk:2.0.1') { // for Mapping SDK MapView; displays route to navigate
exclude group: 'com.android.support' // (note: in your app, you might omit this 'exclude')
}

implementation('com.mapquest:search-ahead-v3:1.2.9') // for the MapQuest "Search Ahead" feature (optional)

implementation('com.mapquest:mapping-android-sdk:1.3.2@aar') {
transitive = true
}
}

3. (Shows up fine in the Preview)

<com.mapquest.mapping.maps.MapView xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/mapquestMapView"
app:mapquest_app_key="xxxMAPQUEST_KEYxxxx"
/>

So far everything compiles without any errors. But when I start my app it crashes with the mentioned message above. So I tried adding the import line as mentioned in my MainActivity. But that doesn't seem to work.

I'm using AndroidStudio 3.1.2 with Linux Mint x64.