e: C:\Users\MS\AndroidStudioProjects\chatting_video\app\src\main\java\Model\Useritem.kt: (3, 18): Unresolved reference: item

e: C:\Users\MS\AndroidStudioProjects\chatting_video\app\src\main\java\Model\Useritem.kt: (4, 5): Expecting member declaration

Useritem.kt

package Model

class Useritem : item<GroupieViewHolder>() {
    return R.layout.message_list_row
}
item이 import가 안되요. GroupieViewHolder가 빨간색이예요.
안드로이드 스튜디오에 GroupieViewHolder가 없어요. 
그냥 제가 키보드로 친거예요. alt+enter눌러도 import가 안떠요.


build gradle

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-android-extensions'
}
apply plugin: 'com.google.gms.google-services'

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.example.chatting_video"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        multiDexEnabled true
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {

    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.2.0'
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'com.google.android.material:material:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.firebase:firebase-auth:19.3.1'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    implementation platform('com.google.firebase:firebase-bom:27.1.0')
    implementation 'com.google.firebase:firebase-analytics'
    implementation platform('com.google.firebase:firebase-bom:26.8.0')
    implementation "com.xwray:groupie:2.7.0"


}

implementation "com.xwray:groupie:$groupie_version"을 붙어넣으면
Build file 'C:\Users\MS\AndroidStudioProjects\chatting_video\app\build.gradle' line: 52

A problem occurred evaluating project ':app'.
> Could not get unknown property 'groupie_version' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.
가 떠요. 에러가 생겨요. 
그리고 전 package에 선생님 강의처럼 주소와 챗팅 비디오 모델이라고 안뜨고,
Model이라고만 떠요. 어떻게 해야하나요?

package Model

class Useritem : item<GroupieViewHolder>() {
return R.layout.message_list_row
}
로 실행하면 e: C:\Users\MS\AndroidStudioProjects\chatting_video\app\src\main\java\Model\Useritem.kt: (4, 1): Expecting member declaration
라는 오류가 떠요.
item을 import하는 것과 Username을 Implement Members하는 것이 안되요 저는 GroupViewHolder 자동입력이 안떠요. 그래서 그 글씨가 빨간색이예요.
e: C:\Users\MS\AndroidStudioProjects\chatting_video\app\src\main\java\Model\Useritem.kt: (4, 1): Expecting member declaration
이 오류 해결좀 해주세요.

Try it out:2.9.0은 어떻게 다운받나요? 2.9.0 코드를 어디에 넣어야 하는지 모르겠어요.

<?xml version="1.0" encoding="UTF-8"?>

-<settings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/SETTINGS/1.0.0" xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">

-<profiles>

-<profile>

-<repositories>

-<repository>

-<snapshots>

<enabled>false</enabled>

</snapshots>

<id>bintray-lisawray-maven</id>

<name>bintray</name>

<url>https://dl.bintray.com/lisawray/maven</url>

</repository>

</repositories>

-<pluginRepositories>

-<pluginRepository>

-<snapshots>

<enabled>false</enabled>

</snapshots>

<id>bintray-lisawray-maven</id>

<name>bintray-plugins</name>

<url>https://dl.bintray.com/lisawray/maven</url>

</pluginRepository>

</pluginRepositories>

<id>bintray</id>

</profile>

</profiles>

-<activeProfiles>

<activeProfile>bintray</activeProfile>

</activeProfiles>

</settings>

이것과

<dependency>

  <groupId>com.xwray</groupId>

  <artifactId>groupie</artifactId>

  <version>2.9.0</version>

  <type>pom</type>

</dependency>

어떤걸 어디에 넣어야 하나요? 어느 파일인지 구체적으로 알려주세요.

return R.layout.message_list_row부분을 지우고 실행하면,

e: C:\Users\MS\AndroidStudioProjects\chatting_video\app\src\main\java\Model\Useritem.kt: (3, 18): Unresolved reference: item

라는 오류가 뜨는데 뭐가 잘못된건가요?

링크 올리는 것보다 자세하게 코드를 써주세요. 링크를 참고하는 것도 좋지만, 자세한 코드도 추가로 써주세요. 링크만 봐서는 잘모르겠어요.