我需要通过我的应用外的任何相关活动打开已下载的文件。
我通过 `DownloadManager` 下载文件到默认文件夹 `Environment.DIRECTORY_DOWNLOADS`。
我在我的活动中注册了 `BroadcastReceiver`，它应该在下载完成后通过意图打开文件：
@Override
public void onReceive(Context context, Intent intent) {
    if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(intent.getAction())) {
        long downloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, 0);
        DownloadManager downloadManager = (DownloadManager) context.getSystemService(DOWNLOAD_SERVICE);
        if (downloadManager != null) {
            Cursor c = downloadManager.query(new DownloadManager.Query().setFilterById(downloadId));
            if (c.moveToFirst()) {
                int columnIndex = c.getColumnIndex(DownloadManager.COLUMN_STATUS);
                if (DownloadManager.STATUS_SUCCESSFUL == c.getInt(columnIndex)) {
                    String uriString = c.getString(c.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));
                    Intent openIntent = new Intent(Intent.ACTION_VIEW);
                    openIntent.setDataAndType(Uri.parse(uriString), getMimeType(uriString));
                    openIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                    context.startActivity(Intent.createChooser(openIntent, "选择应用程序"));
                }
            }
        }
    }
}

java.lang.RuntimeException: 接收广播意图时出错
由 android.os.FileUriExposedException 引发：file:///storage/emulated/0/Download/sample-20.pdf 超出应用程序范围，通过 ClipData.Item.getUri() 公开

@Override
public void onReceive(Context context, Intent intent) {
    if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(intent.getAction())) {
        long downloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, 0);
        DownloadManager downloadManager = (DownloadManager) context.getSystemService(DOWNLOAD_SERVICE);
        if (downloadManager != null) {
            Cursor c = downloadManager.query(new DownloadManager.Query().setFilterById(downloadId));
            if (c.moveToFirst()) {
                int columnIndex = c.getColumnIndex(DownloadManager.COLUMN_STATUS);
                if (DownloadManager.STATUS_SUCCESSFUL == c.getInt(columnIndex)) {
                    String uriString = c.getString(c.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));
                    Intent openIntent = new Intent(Intent.ACTION_VIEW);
                    File file = new File(URI.create(uriString));
                    Uri uri = FileProvider.getUriForFile(context, BuildConfig.APPLICATION_ID + ".fileprovider", file);
                    openIntent.setDataAndType(uri, getMimeType(uriString));
                    openIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
                    context.startActivity(Intent.createChooser(openIntent, "选择应用"));
                }
            }
        }
    }
}
String getMimeType(String path) {
    String type = null;
    String extension = MimeTypeMap.getFileExtensionFromUrl(path);
    if (extension != null) {
        type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
    }
    return type;
}