Watch a ContentProvider for updates

ContentProviderUpdates.kt

import android.database.ContentObserver
import android.net.Uri
import android.os.Handler
import io.reactivex.ObservableEmitter
import io.reactivex.ObservableOnSubscribe

class ContentProviderUpdates(handler: Handler) : ObservableOnSubscribe<Uri>, ContentObserver(handler) {
    private var emitter: ObservableEmitter<Uri>? = null

    override fun subscribe(emitter: ObservableEmitter<Uri>) {
        this.emitter = emitter
    }

    override fun onChange(selfChange: Boolean, uri: Uri?) {
        uri?.apply { emitter?.onNext(this) }
    }
}