是的，上面的代码是可以工作的，但是如果你在Asynctask的onProgressUpdate中更新你的进度条，你按下后退按钮或完成你的活动，Asynctask将失去它与你的UI的跟踪，当你回到你的活动，即使下载正在后台运行，你也不会看到进度条上的更新。因此，OnResume()尝试运行一个线程，如runOnUIThread与一个定时器任务更新进度条的值从AsyncTask运行后台更新。

private void updateProgressBar(){
    Runnable runnable = new updateProgress();
    background = new Thread(runnable);
    background.start();
}

public class updateProgress implements Runnable {
    public void run() {
        while(Thread.currentThread()==background)
            //while (!Thread.currentThread().isInterrupted()) {
            try {
                Thread.sleep(1000); 
                Message msg = new Message();
                progress = getProgressPercentage();        
                handler.sendMessage(msg);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            } catch (Exception e) {
        }
    }
}

private Handler handler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        progress.setProgress(msg.what);
    }
};

当你的活动不可见时，不要忘记销毁线程。

private void destroyRunningThreads() {
    if (background != null) {
        background.interrupt();
        background=null;
    }
}

    private class DownloadTask extends AsyncTask<String, Integer, String> {

        private PowerManager.WakeLock mWakeLock;
        String onlinePathBundle, onlinePathMusic, offlinePathBundle, offlinePathMusic;

        CircleProgressBar progressBar;
        RelativeLayout rl_progress;
        ImageView btn_download;
        TextView tv_progress;

        public DownloadTask(String onlinePathBundle, String onlinePathMusic, String offlinePathBundle, String offlinePathMusic, CircleProgressBar progressBar, RelativeLayout rl_progress, ImageView btn_download,
                            TextView tv_progress) {
            this.offlinePathBundle = offlinePathBundle;
            this.offlinePathMusic = offlinePathMusic;
            this.progressBar = progressBar;
            this.rl_progress = rl_progress;
            this.btn_download = btn_download;
            this.tv_progress = tv_progress;
            this.onlinePathBundle = onlinePathBundle;
            this.onlinePathMusic = onlinePathMusic;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            progressBar.setMax(100);
            rl_progress.setVisibility(View.VISIBLE);
            btn_download.setVisibility(View.GONE);

            PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
            mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, getClass().getName());
            mWakeLock.acquire();
        }

        @Override
        protected String doInBackground(String... sUrl) {
            String firstResult = downTask(onlinePathBundle, 1, offlinePathBundle);
            String seondResult = downTask(onlinePathMusic, 2, offlinePathMusic);
            if (firstResult != null) {
                Toast.makeText(SplashActivity.this, "Download error: " + firstResult, Toast.LENGTH_LONG).show();
                return firstResult;
            } else {
                return seondResult;
            }

        }

        @Override
        protected void onProgressUpdate(Integer... progress) {
            super.onProgressUpdate(progress);
            progressBar.setProgress(progress[0]);
            tv_progress.setText(progress[0] + "%");

        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            rl_progress.setVisibility(View.GONE);
            btn_download.setVisibility(View.VISIBLE);
            if (result != null) {
                Toast.makeText(SplashActivity.this, "Download error: " + result, Toast.LENGTH_LONG).show();
            } else {
                rl_progress.setVisibility(View.GONE);
                btn_download.setVisibility(View.GONE);
            }

        }

        public String downTask(String onlineNewPath, int numberOfTask, String offlineNewPath) {
            InputStream input = null;
            OutputStream output = null;
            HttpURLConnection connection = null;
            try {
                URL url = new URL(onlineNewPath);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();

                // expect HTTP 200 OK, so we don't mistakenly save error report
                // instead of the file
                if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                    return "Server returned HTTP " + connection.getResponseCode()
                            + " " + connection.getResponseMessage();
                }

                // this will be useful to display download percentage
                // might be -1: server did not report the length
                int fileLength = connection.getContentLength();

                // download the file
                input = connection.getInputStream();
                output = new FileOutputStream(offlineNewPath);

                byte data[] = new byte[4096];
                long total = 0;
                int count;
                while ((count = input.read(data)) != -1) {
                    // allow canceling with back button
                    if (isCancelled()) {
                        input.close();
                        return null;
                    }
                    total += count;
                    // publishing the progress....
                    if (fileLength > 0) {// only if total length is known
                        if (numberOfTask == 1) {
                            publishProgress((int) (total * 50 / fileLength));
                        } else if (numberOfTask == 2) {
                            publishProgress(((int) (total * 50 / fileLength)) + 50);
                        }

                    }
                    output.write(data, 0, count);
                }
            } catch (Exception e) {
                return e.toString();
            } finally {
                try {
                    if (output != null)
                        output.close();
                    if (input != null)
                        input.close();
                } catch (IOException ignored) {
                }

                if (connection != null)
                    connection.disconnect();
            }
            return null;
        }
    }

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  
        } 
    }
});

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()
    }

}

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。

重要的

AsyncTask在Android 11中已弃用。

欲了解更多信息，请查看以下帖子

Android AsyncTask API在Android 11中已弃用。有什么替代方案? https://developer.android.com/reference/android/os/AsyncTask

可能应该移动到谷歌建议的并发框架