我正在實現IntentService下載PDF文件，它會向用戶顯示通知downloadStart并在此過程中不斷更新進度，服務運行正常并且進度更新正確，問題是我從“最近”下載停止，甚至沒有顯示錯誤。這是我的DownloadService類：class DownloadService : IntentService("DownloadService") {lateinit var  downloadNotification : DownloadNotificationlateinit var book : BookDataprivate lateinit var fileName : Stringprivate lateinit var fileFolder : Stringprivate lateinit var filePath : Stringlateinit var fileUrl : Stringvar isCancelled = falseprivate lateinit var handler : Handleroverride fun onCreate() {    super.onCreate()    handler = Handler()}override fun onHandleIntent(p0: Intent?) {    book = Gson().fromJson<BookData>(p0?.getStringExtra("book"), BookData::class.java)    downloadNotification = DownloadNotification(this, book.id!!)    init(book)}fun getFilePath() : String {    val directory = File(fileFolder)    if (!directory.exists()) {        directory.mkdirs()    }    return filePath}private fun init(book : BookData) {    fileName = "${book.id}.pdf"    fileFolder = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS).toString() + File.separator + "Libranova/Books/"    filePath = fileFolder + fileName    fileUrl = book.downloadLink!!    startDownload()}private fun startDownload() {    downloadNotification.setTitle(book.name!!).setText("Preparing...").notificationCompat.apply {        downloadNotification.notifyManager(true)        DownloadUtils.downloadFile(this@DownloadService, object : DownloadListener {            override fun onStarted() {                handler.post {                    Toast.makeText(this@DownloadService,"Download Started", Toast.LENGTH_LONG).show()                }            }            override fun onSuccess() {                downloadNotification.onFinishDownload().freeUp().setSuccess().notifyManager(true)            }            override fun onError(message: String) {                downloadNotification.onFinishDownload().freeUp().setError(message).notifyManager(true)            }