Q: Property delegate must have a 'getValue(InventoryApplication, KProperty<*>)' method. None of the following functions is suitable: I stuck at this problem
class InventoryApplication : Application() {

    val database: ItemDatabase by lazy { ItemDatabase.getDatabase(this) }

}

Error class
Code image

A: I had the same issue, i was able to resolve it by going to the ItemRoomDatabase.kt file, change the INSTANCE variable in the companion object, to return a non-null type ItemRoomDatabase? and the getDataBase() function to return a type ItemRoomDatabase, rather than a RoomDatabase return type as requested in the codelab example.
Your final code in the ItemRoomDatabase.kt file should look something like this:
@Database(entities = [Item::class], version = 1, exportSchema = false)
abstract class ItemRoomDatabase : RoomDatabase() {
    abstract fun itemDao(): ItemDao

    companion object {
        @Volatile
        private var INSTANCE: ItemRoomDatabase? = null

        fun getDatabase(context: Context): ItemRoomDatabase {
            return INSTANCE ?: synchronized(this) {
                val instance = Room.databaseBuilder(
                    context.applicationContext,
                    ItemRoomDatabase::class.java,
                    "item_database"
                )
                    .fallbackToDestructiveMigration()
                    .build()

                INSTANCE = instance

                instance
            }
        }
    }
}

