web services - Using safe threads in Android:Escaping networkonmainthread exception

Here, first my application syncs data from server when the data is synchronized to local database I query one table to retrieve its data and from I get uri of picture and I use another background task to download user picture to my sd card and Since my main background thread is boolean type so I am not able to call functionality to fetch image from there itself. If I call method from postexecute then I get NetworkOnMainthread exception
I am stuck in condition where I need to use safe thread below is code

protected void onPreExecute() {
    mDialog = ProgressDialog.show(viewContext, "", "Synchronizing Data",
            true);


};

/*
 * (non-Javadoc)
 * 
 * @see android.os.AsyncTask#doInBackground(Params[])
 */
@Override
protected Boolean doInBackground(Void... arg0) {
    if (type.contains("ferry")) {

        return SynchronizeRepositoryFerry(false);

    } else {
        return SynchronizeRepositories(false, initialSync);
    }
}

/*
 * (non-Javadoc)
 * 

 * @see android.os.AsyncTask#onPostExecute(java.lang.Object)
 */
@Override
protected void onPostExecute(Boolean result) {
    this.syncComplete = result;
    mDialog.dismiss();
    if (type.contains("Dash")) {
        new BackgroundTask().execute();
    }
    else{

        Intent intent = new Intent();
        intent.setClass(viewContext, classType);
        viewContext.startActivity(intent);

    }


}

class BackgroundTask extends AsyncTask {

    ProgressDialog mDialog;

    protected void onPreExecute() {
        mDialog = ProgressDialog.show(viewContext, "", "Loading Images",
                true);
    };

    @Override
    protected Void doInBackground(Void... params) {
        try {

            int id = 0;
            String url = "http://i.zdnet.com/blogs/3-29-androids.jpg";
            com.jumbybay.businessobjects.User user = new com.jumbybay.businessobjects.User();
            DatabaseHelper dbHelper = new DatabaseHelper(viewContext);
            IUserRepository repository = dbHelper.getUserRepository();
            List imageList;
            try {
                imageList = repository.Retrieve();
                for (int i = 0; i < imageList.size(); i++) {
                    user = imageList.get(i);

                    // url = user.getPicture();
                    id = user.getId();
                    savesd(id, url);

                }
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }


        } catch (final Exception e) {

        }
        return null;
    }

    public void savesd(int id, String uri) throws IOException {
        URL url;
        if (uri == null) {
            url = new URL("http://i.zdnet.com/blogs/3-29-androids.jpg");

        } else {
            url = new URL(uri);
        }
        InputStream input = url.openStream();
        try {
            File storagePath = Environment.getExternalStorageDirectory();
            OutputStream output = new FileOutputStream(new File(
                    storagePath, +id + ".jpg"));

            try {

                byte[] buffer = new byte[20000];
                int bytesRead = 0;
                while ((bytesRead = input.read(buffer, 0, buffer.length)) >= 0) {
                    output.write(buffer, 0, bytesRead);
                }
            } finally {
                output.close();
            }
        } catch (Exception e) {


            e.printStackTrace();
        } finally {
            input.close();
        }

    }

    protected void onPostExecute(Void result) {
        mDialog.dismiss();
        Intent intent = new Intent();

        /*
         * intent.setClass(viewContext, classType);
         * viewContext.startActivity(intent);
         */

        intent.setClass(viewContext, classType);
        viewContext.startActivity(intent);

    };
}

Answer

@Override
    protected Boolean doInBackground(Void... arg0) {
        if (type.contains("ferry")) {
            return SynchronizeRepositoryFerry(false);

        } else {
            SynchronizeRepositories(false, initialSync);
            com.jumbybay.businessobjects.User user = new com.jumbybay.businessobjects.User();

            DatabaseHelper dbHelper = new DatabaseHelper(viewContext);
            IUserRepository repository = dbHelper.getUserRepository();
            List imageList;
            try {
                int id;
                String url = "http://i.zdnet.com/blogs/3-29-androids.jpg";
                imageList = repository.Retrieve();
                for (int i = 0; i < imageList.size(); i++) {
                    user = imageList.get(i);
                    // url = user.getPicture();

                    id = user.getId();
                    savesd(id, url);
                }
            } catch (SQLException e) {
                // TODO Auto-generated catch block// url = user.getPicture();
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }


        }
        return SynchronizeRepositories(false, initialSync);
    }