安卓下载管理器进度

Question

我正在开发一个应用程序，用户可以下载不同的内容包。 对于下载过程，我正在使用DownloadManager类。 目前为止一切都很好。

我该如何获取已经通过DownloadManager开始的正在运行的下载的当前进度。 我知道有内置的下载通知等等，但对我来说，必须获取正在运行的下载的进度，以便我可以在我的应用程序中使用它来显示自定义进度条中的进度。

这是否可能，还是我只是瞎了眼找不到解决方案。

- user1003622

Answer 1

我也在寻找更好的方法，但目前打算每秒钟轮询一次以获取进度。

DownloadManager mgr = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
long id = mgr.enqueue(request);

DownloadManager.Query q = new DownloadManager.Query();
q.setFilterById(id);
Cursor cursor = mgr.query(q);
cursor.moveToFirst();
int bytes_downloaded = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR));
cursor.close();

编辑：

可以使用FileObserver来实现这一点。以下是我编写的一个基础模板，可帮助跟踪应用程序已下载的文件。在活动或服务的onStart中启动它并在onStop中停止它。结合在onStart期间对事物状态的手动同步，这可以让您对正在发生的情况有一个相当完整的了解。

特别是要实现进度，监听OPEN/CLOSE_WRITE事件可以帮助您决定何时开始/停止轮询DownloadManager以获取更新。

public class DownloadsObserver extends FileObserver {

    public static final String LOG_TAG = DownloadsObserver.class.getSimpleName();

    private static final int flags =
            FileObserver.CLOSE_WRITE
            | FileObserver.OPEN
            | FileObserver.MODIFY
            | FileObserver.DELETE
            | FileObserver.MOVED_FROM;
    // Received three of these after the delete event while deleting a video through a separate file manager app:
    // 01-16 15:52:27.627: D/APP(4316): DownloadsObserver: onEvent(1073741856, null)

    public DownloadsObserver(String path) {
        super(path, flags);
    }

    @Override
    public void onEvent(int event, String path) {
        Log.d(LOG_TAG, "onEvent(" + event + ", " + path + ")");

        if (path == null) {
            return;
        }

        switch (event) {
        case FileObserver.CLOSE_WRITE:
            // Download complete, or paused when wifi is disconnected. Possibly reported more than once in a row.
            // Useful for noticing when a download has been paused. For completions, register a receiver for 
            // DownloadManager.ACTION_DOWNLOAD_COMPLETE.
            break;
        case FileObserver.OPEN:
            // Called for both read and write modes.
            // Useful for noticing a download has been started or resumed.
            break;
        case FileObserver.DELETE:
        case FileObserver.MOVED_FROM:
            // These might come in handy for obvious reasons.
            break;
        case FileObserver.MODIFY:
            // Called very frequently while a download is ongoing (~1 per ms).
            // This could be used to trigger a progress update, but that should probably be done less often than this.
            break;
        }
    }
}

用法应该像这样：

public class MyActivity extends Activity {

    private FileObserver fileObserver = new DownloadsObserver(
            getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath());

    @Override
    protected void onStart() {
        super.onStart();
        fileObserver.startWatching();
        syncUpDatabaseWithFileSystem();
    }

    @Override
    protected void onStop() {
        fileObserver.stopWatching();
        super.onStop();
    }
}

- dokkaebi

---

在MODIFY情况下，我们应该如何获取下载完成的值？如何知道已下载部分的百分比？ - JVN

对我非常有效！请注意，FileObserver＃onEvent（）在单独的线程上运行。对于任何UI操作（例如更新进度条），您需要执行类似new Handler（Looper.getMainLooper（））。post（new Runnable（）{...}）;这样的操作，并将代码放置在Runnable的run（）方法中。 - user149408

修正：在KitKat上运行得很好，但在Marshmallow上却不行。根据https://dev59.com/21wY5IYBdhLWcg3wq5Qd的说法，这似乎是Marshmallow中的一个错误... - user149408

肯定可以在Android 7上运行。 - Marc

Answer 2

原来在Marshmallow上的FileObserver实现存在一个bug。因此，FileObserver将不会报告下载管理器下载的文件的任何修改。（旧版Android没有这个问题——在KitKat上它可以正常工作。）来源 对我来说，以下代码（基于这个答案）运行良好。我每秒轮询一次——我尝试将间隔减半，但没有看到任何效果。

private static final int PROGRESS_DELAY = 1000;
Handler handler = new Handler();
private boolean isProgressCheckerRunning = false;

// when the first download starts
startProgressChecker();

// when the last download finishes or the Activity is destroyed
stopProgressChecker();

/**
 * Checks download progress.
 */
private void checkProgress() {
    DownloadManager.Query query = new DownloadManager.Query();
    query.setFilterByStatus(~(DownloadManager.STATUS_FAILED | DownloadManager.STATUS_SUCCESSFUL));
    Cursor cursor = downloadManager.query(query);
    if (!cursor.moveToFirst()) {
        cursor.close();
        return;
    }
    do {
        long reference = cursor.getLong(cursor.getColumnIndex(DownloadManager.COLUMN_ID));
        long progress = cursor.getLong(cursor.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR));
        // do whatever you need with the progress
    } while (cursor.moveToNext());
    cursor.close();
}

/**
 * Starts watching download progress.
 * 
 * This method is safe to call multiple times. Starting an already running progress checker is a no-op.
 */
private void startProgressChecker() {
    if (!isProgressCheckerRunning) {
        progressChecker.run();
    isProgressCheckerRunning = true;
    }
}

/**
 * Stops watching download progress.
 */
private void stopProgressChecker() {
    handler.removeCallbacks(progressChecker);
    isProgressCheckerRunning = false;
}

/**
 * Checks download progress and updates status, then re-schedules itself.
 */
private Runnable progressChecker = new Runnable() {
    @Override
    public void run() {
        try {
            checkProgress();
            // manager reference not found. Commenting the code for compilation
            //manager.refresh();
        } finally {
            handler.postDelayed(progressChecker, PROGRESS_DELAY);
        }
    }
};

- user149408