Question

以下代码行崩溃

Room.databaseBuilder(
        applicationContext,
        MyDatabase::class.java, "MyDB")
        .build()

这是您可以轻松复制的“最小完整可验证（MCV）”应用程序

在项目的build.gradle中，确保存在以下内容

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

在应用程序的build.gradle中，确保存在以下内容

dependencies {
    def room_version = "1.1.1"

    implementation "android.arch.persistence.room:runtime:$room_version"
    kapt  "android.arch.persistence.room:compiler:$room_version" // because I'm using Kotlin
}

所有设置说明均根据官方文档https://developer.android.com/topic/libraries/architecture/adding-components

现在只需使用Android Studio并使用“空活动”模板创建项目。在此MCV示例中，仅需要3个新文件。

创建名为MyThing.kt

的第一个文件

//MyThing.kt
import android.arch.persistence.room.ColumnInfo
import android.arch.persistence.room.Entity

@Entity(tableName = "myThing")
data class MyThing(@ColumnInfo var myString: String)

创建另一个名为MyDao.kt的文件

import android.arch.persistence.room.Dao
import android.arch.persistence.room.Insert
import android.arch.persistence.room.OnConflictStrategy

@Dao
interface MyDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insert(myThing: MyThing)
}

创建名为MyDatabase.kt的第三个文件

import android.arch.persistence.room.Database
import android.arch.persistence.room.RoomDatabase

@Database(entities = arrayOf(MyThing::class), version = 1)
abstract class MyDatabase : RoomDatabase() {
    abstract fun myDao(): MyDao
}

现在修改MainActivity类

class MainActivity : AppCompatActivity() {

    private var myDB: MyDatabase? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        myDB = Room.databaseBuilder(
            applicationContext,
            MyDatabase::class.java, "MyDB")
            .build()
    }
}

现在运行该应用程序将导致我上面提到的那行严重崩溃。我在做什么错了？

更新：Logcat输出

--------- beginning of crash 12-29 13:23:46.098 12801-12801/com.le.kevin.roommcv E/AndroidRuntime: FATAL EXCEPTION: main Process: com.le.kevin.roommcv, PID: 12801 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.le.kevin.roommcv/com.le.kevin.roommcv.MainActivity}: java.lang.RuntimeException: cannot find implementation for com.le.kevin.roommcv.MyDatabase. MyDatabase_Impl does not exist at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) at android.app.ActivityThread.-wrap11(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) Caused by: java.lang.RuntimeException: cannot find implementation for com.le.kevin.roommcv.MyDatabase. MyDatabase_Impl does not exist at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:93) at android.arch.persistence.room.RoomDatabase$Builder.build(RoomDatabase.java:630) at com.le.kevin.roommcv.MainActivity.onCreate(MainActivity.kt:19) at android.app.Activity.performCreate(Activity.java:6251) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) at android.app.ActivityThread.-wrap11(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 12-29 13:23:46.099 777-1936/? W/ActivityManager: Force finishing activity com.le.kevin.roommcv/.MainActivity

Impl？

Answer 1

我通过添加

使它起作用

apply plugin: 'kotlin-kapt'

在应用的build.graddle中

我找到了答案，这要看上面评论中建议的logcat，然后再看看答案Room + cannot find implementation DB + DB_Impl does not exist

官方文档https://developer.android.com/topic/libraries/architecture/adding-components不完整

Room databaseBuilder内部版本崩溃

1 个答案: