android-kotlin error : unresolved reference databinding & ActivityMainBinding

问题

I am using Android Studio 3.0 Canary 6 version. I've enabled dataBinding in my class and the code doesn't show any error. But, when I build an APK, the build fails and shows the following error:

Error:(8, 37) Unresolved reference: databinding  
Error:(22, 26) Unresolved reference: ActivityMainBinding  
Error:(38, 50) Unresolved reference: ActivityMainBinding  
Error:(43, 52) Unresolved reference: ActivityMainBinding  
Error:(46, 52) Unresolved reference: ActivityMainBinding  
Error:(49, 52) Unresolved reference: ActivityMainBinding  
Error:(52, 52) Unresolved reference: ActivityMainBinding  
Error:(55, 52) Unresolved reference: ActivityMainBinding  
Error:(58, 52) Unresolved reference: ActivityMainBinding  
Error:(61, 52) Unresolved reference: ActivityMainBinding  
Error:(64, 52) Unresolved reference: ActivityMainBinding  
Error:(67, 52) Unresolved reference: ActivityMainBinding  
Error:(70, 52) Unresolved reference: ActivityMainBinding  
Error:(73, 52) Unresolved reference: ActivityMainBinding  
Error:Execution failed for task ':app:compileDebugKotlin'.  
Compilation error. See log for more details

The top level build.gradle file is as follows :

buildscript {
ext.kotlin_version = '1.1.3-2'
repositories {
    google()
    jcenter()
}
dependencies {
    classpath 'com.android.tools.build:gradle:3.0.0-alpha6'
    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

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

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

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

The module build.gradle file is as follows :

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

apply plugin: 'kotlin-kapt'

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.1"
    defaultConfig {
        applicationId "com.example.jimil.calculator"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner 
            "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 
                'proguard-rules.pro'
        }
    }
    dataBinding{
        enabled =  true
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    androidTestImplementation ('com.android.support.test.espresso:espresso-
        core:3.0.1', {
            exclude group: 'com.android.support', module: 'support-
                annotations'
    })
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    implementation 'com.android.support:appcompat-v7:26.1.0'
    testImplementation 'junit:junit:4.12'
    implementation 'com.android.support.constraint:constraint-layout:1.0.2'
    kapt 'com.android.databinding:compiler:3.0.0-alpha6'
}

kapt {
    generateStubs = true
}

The MainActivity.kt class is :

import com.example.jimil.calculator.databinding.ActivityMainBinding  
...  
class MainActivity : AppCompatActivity() {  
    private var binding: ActivityMainBinding? = null  
    ...  
}

Please help me solve the build error.

回答1:

There are several errors in your gradle.

The current Gradle-Version is 3.0.0-beta 3. That means that you need to change your classpath to

classpath 'com.android.tools.build:gradle:3.0.0-beta6'

Same for your dependencies

kapt "com.android.databinding:compiler:3.0.0-beta6"

You should also provide your plugins in the proper folder.

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-kapt'
apply plugin: 'kotlin-android-extensions'

You should also enable compile options to have your annotation processors use Java8-dependencies (which may be required for Kotlin to target 1.8).

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}

After this is done invalidate your cache and restart.

If the error still persists check the Gradle Console. There may be an error in your XML File which stops your Annotation processor to generate the databinding classes.

回答2:

In my case, cleaning and then rebuilding the project solved the problem. The problem was that the necessary classes haven't been built until then.

Once data binding is integrated in layout file, goto Build -> Clean Project and Build -> Rebuild Project. This will generate necessary binding classes.

source: link

回答3:

I had this issue (Unresolved reference: ActivityMainBinding ) Tweaking dependencies did not work. The issue was I was using a DrawerLayout instead of layout as the root element of the activity layout which I want to generate the data binding for.

So place your other layout(ex: constraint, linear relative layouts) inside following tag

<layout xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools">

<!-- other layout here -->

</layout>

source: https://stackoverflow.com/a/50634021/7356355

回答4:

I forgot to add kotlin-kapt. After adding it, it worked!

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

apply plugin: 'kotlin-kapt'


dependencies {
    kapt "com.android.databinding:compiler:3.1.3"
}

来源：https://stackoverflow.com/questions/46521478/android-kotlin-error-unresolved-reference-databinding-activitymainbinding