Java 使用下载管理器android下载文件。如何检查文件是否完全下载

我一直在开发一个从谷歌硬盘下载pdf并在pdf查看器中打开的应用程序。一旦下载了文件，它就会在pdf查看器中打开文件（如果android手机中有）。您可以通过单击同一链接再次打开该文件

但有时会发生的情况是，由于网络速度慢或其他一些问题，文件下载在这段时间被中断。因此，当用户打开该文件时，会显示“已损坏的文件”

因此，如何删除该文件，并通过应用程序检查该文件是否已损坏

请回复。。 提前谢谢

公共类PDFTools{

private static String file;

private static final String PDF_MIME_TYPE = "application/pdf";
public static ProgressDialog progress = null;

public static boolean isNetworkAvailable(final Context context) {
    final ConnectivityManager connectivityManager = ((ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE));
    return connectivityManager.getActiveNetworkInfo() != null && connectivityManager.getActiveNetworkInfo().isConnected();
}


/**
 * If a PDF reader is installed, download the PDF file and open it in a reader.
 * Otherwise ask the user if he/she wants to view it in the Google Drive online PDF reader.<br />
 * <br />
 * <b>BEWARE:</b> This method
 *
 * @param context
 * @param pdfUrl
 * @return
 */


public static void showPDFUrl(final Context context, final String pdfUrl, final String name) {
    if (isPDFSupported(context)) {
        downloadAndOpenPDF(context, pdfUrl, name);
    } else {
        Toast.makeText(context, "PDF NOT SUPPORTED", Toast.LENGTH_SHORT).show();
    }
    if (pdfUrl == null) {
        Toast.makeText(context, "NOT AVAILABLE", Toast.LENGTH_SHORT).show();
    }
}

/**
 * Downloads a PDF with the Android DownloadManager and opens it with an installed PDF reader app.
 *
 * @param context
 * @param pdfUrl
 */
@TargetApi(Build.VERSION_CODES.GINGERBREAD)
public static void downloadAndOpenPDF(final Context context, final String pdfUrl, final String name) {

    // Get filename
     //final String filename = pdfUrl.substring( pdfUrl.lastIndexOf( "/" ) + 1 );
    // The place where the downloaded PDF file will be put

    final File tempFile = new File(context.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS), name);

    if (tempFile.exists()) {

        try {
            boolean bool = tempFile.canRead();
            // If we have downloaded the file before, just go ahead and show it.
            if (bool) {
                openPDF(context, Uri.fromFile(tempFile));
                return;
            }else{
                tempFile.delete();
            }
        } catch (SecurityException e) {
            e.printStackTrace();
        }
    }


    // Show progress dialog while downloading
    if (PDFTools.isNetworkAvailable(context)) {
        progress = ProgressDialog.show(context, context.getString(R.string.pdf_show_local_progress_title), context.getString(R.string.pdf_show_local_progress_content), true);
        progress.setCanceledOnTouchOutside(true);


        // Create the download request
        DownloadManager.Request r = new DownloadManager.Request(Uri.parse(pdfUrl));
        r.setDestinationInExternalFilesDir(context, Environment.DIRECTORY_DOWNLOADS, name);
        r.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        r.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI | DownloadManager.Request.NETWORK_MOBILE);
        r.setVisibleInDownloadsUi(true);
        r.allowScanningByMediaScanner();
        final DownloadManager dm = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
        BroadcastReceiver onComplete = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                if (!progress.isShowing()) {
                    return;
                }
                context.unregisterReceiver(this);

                progress.dismiss();
                long downloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
                Cursor cursor = dm.query(new DownloadManager.Query().setFilterById(downloadId));
                Log.d("filepath", Environment.getExternalStorageState());


                if (cursor.moveToFirst()) {
                    Log.d("In move to first", "Inside first if");

                    int status = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS));
                    int reason = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_REASON));
                    if (cursor.moveToFirst()) {
                        if (cursor.getCount() > 0) {

                            if (status == DownloadManager.STATUS_SUCCESSFUL) {
                                file = cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME));
                                // So something here on success
                            } else {
                                int message = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_REASON));
                                File file1 = new File(file);
                                file1.delete();
                            }
                        }
                    }
                }

                cursor.close();
            }
        };
        context.registerReceiver(onComplete, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
        dm.enqueue(r);
        // Enqueue the request

---

}

如果（status==DownloadManager.status\u SUCCESSFUL）不起作用，是否存在

的原因？当文件完全下载时，它就起作用了。当出现网络问题时，下载会在中间停止，控件不会进入if（状态==DownloadManager.status\u SUCCESSFUL）。当下载文件时出现网络问题时，下载会在两者之间停止，然后单击同一链接会出现文件损坏错误
    } else {

        Toast.makeText(context, "Check Your Network Connectivity",


                Toast.LENGTH_LONG).show();
    }


}


/**
 * Show a dialog asking the user if he wants to open the PDF through Google Drive
 * @param context
 * @param pdfUrl
 */

/**
 * Open a local PDF file with an installed reader
 *
 * @param context
 * @param localUri
 */
public static final void openPDF(Context context, Uri localUri) {
    Intent i = new Intent(Intent.ACTION_VIEW);
    i.setDataAndType(localUri, PDF_MIME_TYPE);
    try {
        context.startActivity(i);
    } catch (Exception e) {
        File file1 = new File(file);
        file1.delete();
    }
}

/**
 * Checks if any apps are installed that supports reading of PDF files.
 *
 * @param context
 * @return
 */
public static boolean isPDFSupported(Context context) {
    Intent i = new Intent(Intent.ACTION_VIEW);
    final File tempFile = new File(context.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS), "test.pdf");
    i.setDataAndType(Uri.fromFile(tempFile), PDF_MIME_TYPE);
    return context.getPackageManager().queryIntentActivities(i, PackageManager.MATCH_DEFAULT_ONLY).size() > 0;
}