在活动中显示下载管理器进度

Question

我在我的活动中使用了Download Manager类来执行下载；它工作得很好，我的下一个任务是在我的活动中显示相同的进度百分比。我不知道该怎么做。

到目前为止我的代码

public class DownloadSampleBook extends Activity{

private long enqueue;
private DownloadManager dm;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_sample_download);

    BroadcastReceiver receiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {
                long downloadId = intent.getLongExtra(
                        DownloadManager.EXTRA_DOWNLOAD_ID, 0);
                Query query = new Query();
                query.setFilterById(enqueue);
                Cursor c = dm.query(query);
                if (c.moveToFirst()) {
                    int columnIndex = c
                            .getColumnIndex(DownloadManager.COLUMN_STATUS);
                    if (DownloadManager.STATUS_SUCCESSFUL == c
                            .getInt(columnIndex)) {

                       view.setImageURI(Uri.parse(uriString));
                    }
                }
            }
        }
    };

    registerReceiver(receiver, new IntentFilter(
            DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}

public void onClick(View view) {
    dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
    Request request = new Request(
            Uri.parse("http://abc.com/a.png"));
    enqueue = dm.enqueue(request);

}

public void showDownload(View view) {
    Intent i = new Intent();
    i.setAction(DownloadManager.ACTION_VIEW_DOWNLOADS);
    startActivity(i);
}
}

有没有给出进度下载百分比的方法？

Answer 1

如果您正在寻找一种合适的方法来确定何时查询DownloadManager以获取进度更新，请考虑为uri content://downloads/my_downloads注册一个ContentObserver。

示例：

DownloadManager manager = (DownloadManager) getSystemService( Context.DOWNLOAD_SERVICE );
manager.enqueue( myRequest );

Uri myDownloads = Uri.parse( "content://downloads/my_downloads" );
getContentResolver().registerContentObserver( myDownloads, true, new DownloadObserver() );

...

public static class DownloadObserver extends ContentObserver {
   @Override
   public void onChange( boolean selfChange, Uri uri ) {
      Log.d( "DownloadObserver", "Download " + uri + " updated" );
   }

当接收到长时间运行的下载的每个块时，这将产生以下输出

D/DownloadObserver(15584): Download content://downloads/my_downloads/437 updated
D/DownloadObserver(15584): Download content://downloads/my_downloads/437 updated
D/DownloadObserver(15584): Download content://downloads/my_downloads/437 updated
D/DownloadObserver(15584): Download content://downloads/my_downloads/437 updated

其中'437‘是您下载的ID。

请注意，这遵循类android.provider.Downloads中定义的内容URI，它似乎隐藏在框架中，并且可能并不是在所有设备上都一致地工作。(https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/core/java/android/provider/Downloads.java#89)

Answer 2

您可以使用query方法查询到目前为止已下载的字节数和需要下载的总字节数，方法与在示例代码中查询状态的方式大致相同。一旦有了这些值，就很容易以百分比的形式计算进度。

当收到新数据时，似乎没有任何方法通知您，因此，您可以定期轮询下载管理器，以确定您想要监控的任何下载的当前状态。

Query query = new Query();
query.setfilterById(downloadId);

Cursor c = dm.query(query);
if (c.moveToFirst()) {
  int sizeIndex = c.getColumnIndex(DownloadManager.COLUMN_TOTAL_SIZE_BYTES);
  int downloadedIndex = c.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR);
  long size = c.getInt(sizeIndex);
  long downloaded = c.getInt(downloadedIndex);
  double progress = 0.0;
  if (size != -1) progress = downloaded*100.0/size;  
  // At this point you have the progress as a percentage.
}

请注意，总大小最初为-1，并且仅在下载开始后才会填写。因此，在上面的示例代码中，我检查了-1，如果尚未设置大小，则将进度设置为0。

但是，在某些情况下，您可能会发现从不返回总大小(例如，在HTTP分块传输中，将没有可用于确定大小的Content-Length头部)。如果您需要支持这种类型的服务器，您可能应该向用户提供某种类型的指示，表明下载正在进行，而不仅仅是一个停留在零的进度条。

Answer 3

我有一个跟踪下载多个文件的需求。经过大量的思考和实验，我想出了以下代码：

private void startDownloadThread(final List<DownloadFile> list) {

        // Initializing the broadcast receiver ...
        mBroadCastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                mFinishedFilesFromNotif.add(intent.getExtras()
                        .getLong(DownloadManager.EXTRA_DOWNLOAD_ID));
            }
        };

        IntentFilter intentFilter = new IntentFilter(
                "android.intent.action.DOWNLOAD_COMPLETE");
        DownloadProgressUIFragment.this.getActivity().registerReceiver(mBroadCastReceiver,
                intentFilter);

        // initializing the download manager instance ....
        mDownloadManager = (DownloadManager) getActivity()
                .getSystemService(Context.DOWNLOAD_SERVICE);

        // adding files to the download manager list ...
        for(DownloadFile f: list) {
            mDownloadIds.add(FileUtils.addFileForDownloadInBkg(getApplicationContext(),
                    f.getUrl(),
                    f.getPath()));
        }

        // starting the thread to track the progress of the download ..
        mProgressThread = new Thread(new Runnable() {
            @Override
            public void run() {

                // Preparing the query for the download manager ...
                DownloadManager.Query q = new DownloadManager.Query();
                long[] ids = new long[mDownloadIds.size()];
                final List<Long> idsArrList= new ArrayList<>();
                int i = 0;
                for (Long id: mDownloadIds) {
                    ids[i++] = id;
                    idsArrList.add(id);
                }
                q.setFilterById(ids);

                // getting the total size of the data ...
                Cursor c;

                while(true) {

                    // check if the downloads are already completed ...
                    // Here I have created a set of download ids from download manager to keep
                    // track of all the files that are dowloaded, which I populate by creating
                    //
                    if(mFinishedFilesFromNotif.containsAll(idsArrList)) {
                        isDownloadSuccess = true;

                        // TODO - Take appropriate action. Download is finished successfully
                        return;
                    }

                    // start iterating and noting progress ..
                    c = mDownloadManager.query(q);
                    if(c != null) {
                        int filesDownloaded = 0;
                        float fileFracs = 0f; // this stores the fraction of all the files in
                        // download
                        final int columnTotalSize = c.getColumnIndex
                                (DownloadManager.COLUMN_TOTAL_SIZE_BYTES);
                        final int columnStatus = c.getColumnIndex(DownloadManager.COLUMN_STATUS);
                        //final int columnId = c.getColumnIndex(DownloadManager.COLUMN_ID);
                        final int columnDwnldSoFar =
                                c.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR);

                        while (c.moveToNext()) {
                            // checking the progress ..
                            if(c.getInt(columnStatus) == DownloadManager.STATUS_SUCCESSFUL) {
                                filesDownloaded++;
                            }
                            // If the file is partially downloaded, take its fraction ..
                            else if(c.getInt(columnTotalSize) > 0) {
                                fileFracs += ((c.getInt(columnDwnldSoFar) * 1.0f) /
                                        c.getInt(columnTotalSize));
                            } else if(c.getInt(columnStatus) == DownloadManager.STATUS_FAILED) {
                                // TODO - Take appropriate action. Error in downloading one of the
                                // files.
                                return;
                            }
                        }

                        c.close();

                        // calculate the progress to show ...
                        float progress = (filesDownloaded + fileFracs)/ids.length;

                        // setting the progress text and bar...
                        final int percentage = Math.round(progress * 100.0f);
                        final String txt = "Loading ... " + percentage + "%";

                        // Show the progress appropriately ...
                    }
                }
            }
        });

        mProgressThread.start();
    }

进入文件队列的函数是：

public static long addFileForDownloadInBkg(Context context, String url, String savePath) {
        Uri uri = Uri.parse(url);
        DownloadManager.Request request = new DownloadManager.Request(uri);
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_HIDDEN);
        request.setDestinationUri(Uri.fromFile(new File(savePath)));

        final DownloadManager m = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
        return m.enqueue(request);
    }

基本上，我会分别收到下载已完成的每个文件的通知，然后将它们添加到一个集合中，该集合基本上就是帮助我确定所有下载是否都已完成的集合。我根据文件的数量和每个文件的完成程度来跟踪进度。我希望这能帮到你。