Room cannot find implementation

Question

I have a problem with testing a Room database: when I run the test, I get this exception:

java.lang.RuntimeException: cannot find implementation for database.TicketDatabase. TicketDatabase_Impl does not exist at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:92) at android.arch.persistence.room.RoomDatabase$Builder.build(RoomDatabase.java:454) at com.sw.ing.gestionescontrini.DatabaseTest.setDatabase(DatabaseTest.java:36) at java.lang.reflect.Method.invoke(Native Method) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:24) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runners.Suite.runChild(Suite.java:128) at org.junit.runners.Suite.runChild(Suite.java:27) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at org.junit.runner.JUnitCore.run(JUnitCore.java:115) at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:59) at android.support.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:262) at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1886) 

Class DatabaseTest:

public class DatabaseTest {      TicketDatabase database;     DAO ticketDAO;       @Before     public void setDatabase() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {         Context context = InstrumentationRegistry.getTargetContext();         database = Room.inMemoryDatabaseBuilder(context, TicketDatabase.class).build();          Method method = TicketDatabase.class.getDeclaredMethod("ticketDao()");         method.setAccessible(true);         ticketDAO = (DAO) method.invoke(database, null);     } } 

gradle file:

apply plugin: 'com.android.application'  android {     compileSdkVersion 26     buildToolsVersion '26.0.2'     defaultConfig {         applicationId "com.sw.ing.gestionescontrini"         minSdkVersion 15         targetSdkVersion 26         versionCode 1         versionName "1.0"         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"     }     defaultConfig {         multiDexEnabled true     }     buildTypes {         release {             minifyEnabled false             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'         }     } }  dependencies {     compile fileTree(dir: 'libs', include: ['*.jar'])     androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {         exclude group: 'com.android.support', module: 'support-annotations'     })     compile 'com.android.support:appcompat-v7:26.+'     compile 'com.android.support.constraint:constraint-layout:1.0.2'     testCompile 'junit:junit:4.12'      annotationProcessor 'android.arch.lifecycle:compiler:1.0.0'     compile 'android.arch.persistence.room:rxjava2:1.0.0-rc1'     testCompile'android.arch.persistence.room:testing:1.0.0-rc1'  } 

I don't really know what this implementation should be, I searched for a solution but all I found doesn't work for me. For instance, many found a solution adding kapt "android.arch.persistence.room..." but gradle doesn't recognize "kapt".

Answer 1

kapt is for Kotlin.

First, add:

annotationProcessor "android.arch.persistence.room:compiler:1.0.0" 

to your dependencies closure.

Then, upgrade android.arch.persistence.room:rxjava2 and android.arch.persistence.room:testing to 1.0.0 instead of 1.0.0-rc1.

ref: https://developer.android.com/jetpack/androidx/releases/room

Answer 2

for Kotlin change the 'annotationProcessor' keyword to 'kapt' in gradle file.

kapt "android.arch.persistence.room:compiler:1.1.1" 

and also add on top of the dependency file

apply plugin: 'kotlin-kapt'

ref: https://developer.android.com/jetpack/androidx/releases/room