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;
        }
    }

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;
    }
}

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()
    }

}

我已经修改了AsyncTask类来处理progressDialog在同一上下文中的创建。我认为下面的代码将更可重用。 (它可以从任何活动调用，只要传递上下文，目标文件，对话框消息)

public static class DownloadTask extends AsyncTask<String, Integer, String> {
    private ProgressDialog mPDialog;
    private Context mContext;
    private PowerManager.WakeLock mWakeLock;
    private File mTargetFile;
    //Constructor parameters :
    // @context (current Activity)
    // @targetFile (File object to write,it will be overwritten if exist)
    // @dialogMessage (message of the ProgresDialog)
    public DownloadTask(Context context,File targetFile,String dialogMessage) {
        this.mContext = context;
        this.mTargetFile = targetFile;
        mPDialog = new ProgressDialog(context);

        mPDialog.setMessage(dialogMessage);
        mPDialog.setIndeterminate(true);
        mPDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mPDialog.setCancelable(true);
        // reference to instance to use inside listener
        final DownloadTask me = this;
        mPDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
            @Override
            public void onCancel(DialogInterface dialog) {
                me.cancel(true);
            }
        });
        Log.i("DownloadTask","Constructor done");
    }

    @Override
    protected String doInBackground(String... sUrl) {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            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();
            }
            Log.i("DownloadTask","Response " + connection.getResponseCode());

            // 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(mTargetFile,false);

            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                // allow canceling with back button
                if (isCancelled()) {
                    Log.i("DownloadTask","Cancelled");
                    input.close();
                    return null;
                }
                total += count;
                // publishing the progress....
                if (fileLength > 0) // only if total length is known
                    publishProgress((int) (total * 100 / fileLength));
                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;
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // take CPU lock to prevent CPU from going off if the user
        // presses the power button during download
        PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                getClass().getName());
        mWakeLock.acquire();

        mPDialog.show();

    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        // if we get here, length is known, now set indeterminate to false
        mPDialog.setIndeterminate(false);
        mPDialog.setMax(100);
        mPDialog.setProgress(progress[0]);

    }

    @Override
    protected void onPostExecute(String result) {
        Log.i("DownloadTask", "Work Done! PostExecute");
        mWakeLock.release();
        mPDialog.dismiss();
        if (result != null)
            Toast.makeText(mContext,"Download error: "+result, Toast.LENGTH_LONG).show();
        else
            Toast.makeText(mContext,"File Downloaded", Toast.LENGTH_SHORT).show();
    }
}

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。

我推荐你使用我的Project Netroid，它是基于Volley的。我添加了一些功能，如多事件回调，文件下载管理。这可能会有帮助。