安卓：在后台下载文件

Question

我想从互联网上下载文件并将其存储在外部存储器中。主要的问题是它应该像市场一样在后台下载，当点击安装时，它将下载apk文件。如果有人有任何想法，请告诉我。

谢谢。

- Sameer Z.

Answer 1

这是另一段使用异步任务和持续通知下载文件的代码。

public class DownloadTask extends AsyncTask<Integer, Integer, Void>{
    private NotificationHelper mNotificationHelper;

    private static final String PEFERENCE_FILE = "preference";
    private static final String ISDOWNLOADED = "isdownloaded";
    SharedPreferences settings;
    SharedPreferences.Editor editor;
    Context context;
    public DownloadTask(Context context){
        this.context = context;
        mNotificationHelper = new NotificationHelper(context);
    }

    protected void onPreExecute(){
        //Create the notification in the statusbar
        mNotificationHelper.createNotification();
    }

    @Override
    protected Void doInBackground(Integer... integers) {
        //This is where we would do the actual download stuff
        //for now I'm just going to loop for 10 seconds
        // publishing progress every second

        int count;

        try {


         URL url = new URL("filename url");
        URLConnection connexion = url.openConnection();
        connexion.connect();

        int lenghtOfFile = connexion.getContentLength();
        Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);

        InputStream input = new BufferedInputStream(url.openStream());
        //OutputStream output = new FileOutputStream("/sdcard/foldername/temp.zip");
        OutputStream output = new FileOutputStream("/sdcard/foldername/himages.zip");
        byte data[] = new byte[1024];

        long total = 0;

            while ((count = input.read(data)) != -1) {
                total += count;
                //publishProgress(""+(int)((total*100)/lenghtOfFile));
                Log.d("%Percentage%",""+(int)((total*100)/lenghtOfFile));
                onProgressUpdate((int)((total*100)/lenghtOfFile));
                output.write(data, 0, count);
            }

            output.flush();
            output.close();
            input.close();
            File file = new File(Environment.getExternalStorageDirectory()
                    + "/foldername/"+"_images.zip"); 
            File path = new File(Environment.getExternalStorageDirectory()
                    + "/foldername"); 
                try {
                        ZipUtil.unzip(file,path);
                        settings = this.context.getSharedPreferences(PEFERENCE_FILE, 0);
                        editor = settings.edit();
                        editor.putBoolean(ISDOWNLOADED, true);
                        editor.commit();

                } catch (IOException e) {
                        Log.d("ZIP UTILL",e.toString());
                    }

        } catch (Exception e) {}


        return null;
    }
    protected void onProgressUpdate(Integer... progress) {
        //This method runs on the UI thread, it receives progress updates
        //from the background thread and publishes them to the status bar
        mNotificationHelper.progressUpdate(progress[0]);
    }
    protected void onPostExecute(Void result)    {
        //The task is complete, tell the status bar about it
        HyundaiApplication.serviceState=false;
        mNotificationHelper.completed();
    }
}

这是通知助手。

public class NotificationHelper {
    private Context mContext;
    private int NOTIFICATION_ID = 1;
    private Notification mNotification;
    private NotificationManager mNotificationManager;
    private PendingIntent mContentIntent;
    private CharSequence mContentTitle;
    public NotificationHelper(Context context)
    {
        mContext = context;
    }

    /**
     * Put the notification into the status bar
     */
    public void createNotification() {
        //get the notification manager
        mNotificationManager = (NotificationManager) mContext.getSystemService(Context.NOTIFICATION_SERVICE);

        //create the notification
        int icon = android.R.drawable.stat_sys_download;
        CharSequence tickerText = mContext.getString(R.string.download_ticker); //Initial text that appears in the status bar
        long when = System.currentTimeMillis();
        mNotification = new Notification(icon, tickerText, when);

        //create the content which is shown in the notification pulldown
        mContentTitle = mContext.getString(R.string.content_title); //Full title of the notification in the pull down
        CharSequence contentText = "0% complete"; //Text of the notification in the pull down

        //you have to set a PendingIntent on a notification to tell the system what you want it to do when the notification is selected
        //I don't want to use this here so I'm just creating a blank one
        Intent notificationIntent = new Intent();
        mContentIntent = PendingIntent.getActivity(mContext, 0, notificationIntent, 0);

        //add the additional content and intent to the notification
        mNotification.setLatestEventInfo(mContext, mContentTitle, contentText, mContentIntent);

        //make this notification appear in the 'Ongoing events' section
        mNotification.flags = Notification.FLAG_ONGOING_EVENT;

        //show the notification
        mNotificationManager.notify(NOTIFICATION_ID, mNotification);
    }

    /**
     * Receives progress updates from the background task and updates the status bar notification appropriately
     * @param percentageComplete
     */
    public void progressUpdate(int percentageComplete) {
        //build up the new status message
        CharSequence contentText = percentageComplete + "% complete";
        //publish it to the status bar
        mNotification.setLatestEventInfo(mContext, mContentTitle, contentText, mContentIntent);
        mNotificationManager.notify(NOTIFICATION_ID, mNotification);
    }

    /**
     * called when the background task is complete, this removes the notification from the status bar.
     * We could also use this to add a new ‘task complete’ notification
     */
    public void completed()    {
        //remove the notification from the status bar
        mNotificationManager.cancel(NOTIFICATION_ID);
    }
}

谢谢。

- Sameer Z.

---

这段代码非常错误：onProgressUpdate((int)((total*100)/lenghtOfFile));。你正在从工作线程中调用该方法，而不是UI线程。请改用publishProgress()。 - JohnD

Answer 2

如果您的应用程序使用2.3，则可以使用Android SDK提供的DownloadManager API。否则，您可以编写自己的服务来实现此目的。

- mudit

---

请告诉我如何在2.1和2.2中实现DownloadManager，我已经使用服务进行了一些工作，但不知道如何下载文件，如果有任何链接，请发送给我。 - Sameer Z.

DownloadManager仅在2.3及以上版本中可用。因此，对于较低的API版本，请使用Chirag提供的链接。 - mudit

Answer 3

由于安卓是开源的，你可以在较低版本的安卓系统中移植下载管理器，只需要简单地将安卓2.3中的下载管理器移植即可。

- shaobin0604

Answer 4

请查找此链接。它解释了如何从互联网下载文件。您必须将此代码放入线程中。它用于后台进程。您应该参考线程进行后台处理，或使用AsyncTask，它也用于后台处理。

- Chirag