您可以使用LiveData和协程观察下载管理器的进度，参见下面的要点

https://gist.github.com/FhdAlotaibi/678eb1f4fa94475daf74ac491874fc0e

data class DownloadItem(val bytesDownloadedSoFar: Long = -1, val totalSizeBytes: Long = -1, val status: Int)

class DownloadProgressLiveData(private val application: Application, private val requestId: Long) : LiveData<DownloadItem>(), CoroutineScope {

    private val downloadManager by lazy {
        application.getSystemService(Context.DOWNLOAD_SERVICE) as DownloadManager
    }

    private val job = Job()

    override val coroutineContext: CoroutineContext
        get() = Dispatchers.IO + job

    override fun onActive() {
        super.onActive()
        launch {
            while (isActive) {
                val query = DownloadManager.Query().setFilterById(requestId)
                val cursor = downloadManager.query(query)
                if (cursor.moveToFirst()) {
                    val status = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS))
                    Timber.d("Status $status")
                    when (status) {
                        DownloadManager.STATUS_SUCCESSFUL,
                        DownloadManager.STATUS_PENDING,
                        DownloadManager.STATUS_FAILED,
                        DownloadManager.STATUS_PAUSED -> postValue(DownloadItem(status = status))
                        else -> {
                            val bytesDownloadedSoFar = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR))
                            val totalSizeBytes = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_TOTAL_SIZE_BYTES))
                            postValue(DownloadItem(bytesDownloadedSoFar.toLong(), totalSizeBytes.toLong(), status))
                        }
                    }
                    if (status == DownloadManager.STATUS_SUCCESSFUL || status == DownloadManager.STATUS_FAILED)
                        cancel()
                } else {
                    postValue(DownloadItem(status = DownloadManager.STATUS_FAILED))
                    cancel()
                }
                cursor.close()
                delay(300)
            }
        }
    }

    override fun onInactive() {
        super.onInactive()
        job.cancel()
    }

}

使用Android查询库，确实很酷。你可以改变它使用ProgressDialog，就像你在其他例子中看到的那样，这个将从你的布局中显示进度视图，并在完成后隐藏它。

File target = new File(new File(Environment.getExternalStorageDirectory(), "ApplicationName"), "tmp.pdf");
new AQuery(this).progress(R.id.progress_view).download(_competition.qualificationScoreCardsPdf(), target, new AjaxCallback<File>() {
    public void callback(String url, File file, AjaxStatus status) {
        if (file != null) {
            // do something with file  
        } 
    }
});

不要忘记用新文件("/mnt/sdcard/…")替换"/sdcard…"，否则你会得到一个FileNotFoundException

当我开始学习android开发时，我知道ProgressDialog是正确的方法。ProgressDialog的setProgress方法可以在下载文件时调用它来更新进度级别。

我在许多应用程序中看到的最好的情况是，它们自定义了进度对话框的属性，使进度对话框的外观和感觉比库存版本更好。很好地保持用户的一些动画，如青蛙，大象或可爱的猫/小狗。任何有进度对话框的动画都能吸引用户，他们不喜欢长时间等待。

我个人的建议是使用进度对话框并在执行前进行构建，或者在OnPreExecute()上初始化，如果你使用进度对话框的水平风格的进度条，则经常发布进度。剩下的部分是优化doInBackground的算法。

如果你要从网上下载东西，别忘了给你的manifest文件添加权限!

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.helloandroid"
    android:versionCode="1"
    android:versionName="1.0">

        <uses-sdk android:minSdkVersion="10" />

        <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
        <uses-permission android:name="android.permission.INTERNET"></uses-permission>
        <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
        <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>

        <application 
            android:icon="@drawable/icon" 
            android:label="@string/app_name" 
            android:debuggable="true">

        </application>

</manifest>