toLiveData无法从Android中的DataSource.Factory获得'；s寻呼

我正在尝试使用LiveData从我的房间数据库中分页数据。Google的示例代码表明使用了toLiveData函数：

class ConcertViewModel(concertDao: ConcertDao) : ViewModel() {
    val concertList: LiveData<PagedList<Concert>> =
            concertDao.concertsByDate().toLiveData(pageSize = 50)
}

ConnectionsViewModel.kt

import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.paging.DataSource
import androidx.paging.PagedList
import com.linkedintools.da.local.room.AppDao
import com.example.model.UserConnection
import javax.inject.Inject

class ConnectionsViewModel @Inject constructor(appDao: AppDao) : ViewModel() {

    val connectionsDataSource : DataSource.Factory<Int, UserConnection> = appDao.connectionsByFirstName()

    val concertList: LiveData<PagedList<UserConnection>> = connectionsDataSource.toLiveData(pageSize = 40)

}

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toLiveData不可用。我是做错了什么，还是谷歌的示例代码已经过时了？

toLiveData是一个很有趣的扩展，导入这个库，一切都完成了：
分页：分页运行时ktx:2.1.0-rc01

另外，请检查此google示例项目

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谢谢！在阅读您的答案之前，我不知道androidx的*-ktx库。请仔细阅读这些评论-->

import androidx.room.Database
import androidx.room.RoomDatabase
import androidx.room.TypeConverters
import com.example.model.UserConnection

@Database(entities = arrayOf(UserConnection::class), version = 1, exportSchema = true)
@TypeConverters(RoomConverters::class)
abstract class AppDatabase : RoomDatabase() {
    abstract fun appDao(): AppDao
}

import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.paging.DataSource
import androidx.paging.PagedList
import com.linkedintools.da.local.room.AppDao
import com.example.model.UserConnection
import javax.inject.Inject

class ConnectionsViewModel @Inject constructor(appDao: AppDao) : ViewModel() {

    val connectionsDataSource : DataSource.Factory<Int, UserConnection> = appDao.connectionsByFirstName()

    val concertList: LiveData<PagedList<UserConnection>> = connectionsDataSource.toLiveData(pageSize = 40)

}

dependencies {
    def room_version = "2.1.0-rc01"
    def paging_version = "2.1.0"

    implementation "androidx.room:room-runtime:$room_version"
    kapt "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor

    // optional - Kotlin Extensions and Coroutines support for Room
    implementation "androidx.room:room-ktx:$room_version"

    // optional - RxJava support for Room
    implementation "androidx.room:room-rxjava2:$room_version"

    // Paging
    implementation "androidx.paging:paging-runtime:$paging_version"

}