Example2_Solution.kt

data class SimpleContact(val displayName: String, val isStarred: Boolean) {
    companion object {
        fun from(cursor: Cursor) =
            SimpleContact(
                cursor.getString(cursor.getColumnIndex(Contacts.DISPLAY_NAME)),
                cursor.getInt(cursor.getColumnIndex(Contacts.STARRED)) == 1)
    }
}

fun contacts(contentResolver: ContentResolver): Flowable<SimpleContact> =
    contentResolver.uriChangesOf(
        {
            itemsFor(
                { query(Contacts.CONTENT_URI,
                        arrayOf(Contacts.DISPLAY_NAME, Contacts.STARRED),
                        null, null, "${Contacts.DISPLAY_NAME} ASC") },
                { SimpleContact.from(it) }
            )
        }, Contacts.CONTENT_URI)
        .subscribeOn(AndroidSchedulers.mainThread())
        .observeOn(Schedulers.io())
        .switchMap { obs -> obs }