BackgroundWorker in WPF not working

Question

I have a button that navigates a web page. I was trying to put the navigation in a backgroundworker, but it doesn't navigate. If I put it in the click event of the button it works fine. I put a break point in the bgw_DoWork and it shows that it hits the point of creating a new wb object, however it skips the rest of the statements in the DoWork. I wanted to do this so that I can display a loading image while it is trying to get data from a web page. The webbrowser object is not part of the UI as the user doesn't need to see the scraping. It just downloads the information into an object and then later displays the object (outside of the BackgroundWorker).

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;
using System.Windows;
using System.Windows.Threading;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Reflection;
using System.ComponentModel;
using mshtml;

namespace WPF1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {


        WebBrowser wb;
        private readonly BackgroundWorker bgw = new BackgroundWorker();

        public int i = 0;

        public MainWindow()
        {
            InitializeComponent();
            bgw.DoWork += bgw_DoWork;
            bgw.RunWorkerCompleted += bgw_RunWorkerCompleted;

       }

        private void GetSICData_Click(object sender, RoutedEventArgs e)
        {
            //mainTabControl.SelectedIndex = 1;

            //wb.Navigated += wb_Navigated;
            //wb.LoadCompleted += wb_LoadCompleted;
            //wb.Navigate("http://www.google.com");

            bgw.RunWorkerAsync();

        }

        private void bgw_DoWork(object sender, DoWorkEventArgs e)
        {
            wb = new WebBrowser();

            wb.Navigated += wb_Navigated;
            wb.LoadCompleted += wb_LoadCompleted;
            wb.Navigate("http://www.google.com");

        }

        private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            MessageBox.Show("Background Complete");
        }

        void wb_LoadCompleted(object sender, NavigationEventArgs e)
        {

            HTMLDocument doc = (HTMLDocument)wb.Document;
            doc.getElementById("ctl03_TextBox1").innerText = "2334882";

            wb.LoadCompleted -= wb_LoadCompleted;
            wb.LoadCompleted += wb_LoadCompleted_2;

            doc.getElementById("ImageButton1").click();

        }

        void wb_LoadCompleted_2(object sender, NavigationEventArgs e)
        {
            MessageBox.Show("It Worked!");
        }

        void wb_Navigated(object sender, NavigationEventArgs e)
        {

        }

    }
}

Answer 1

It sounds like what you really want is the WebClient Class. You can use a number of its methods to download either the whole web page as a file, or as a string. The best part is that you can also do this asynchronously, so it will all happen on a background thread automatically.

When using these asynchronous methods, you need to handle the relevant Download...Completed event to retrieve the results. From the DownloadStringCompletedEventHandler Delegate page on MSDN:

public static void DownloadStringInBackground2 (string address)
{
    WebClient client = new WebClient ();
    Uri uri = new Uri(address);

    // Specify that the DownloadStringCallback2 method gets called 
    // when the download completes.
    client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(
DownloadStringCallback2);
    client.DownloadStringAsync (uri);
}

private static void DownloadStringCallback2 (Object sender, 
DownloadStringCompletedEventArgs e)
{
    // If the request was not canceled and did not throw 
    // an exception, display the resource. 
    if (!e.Cancelled && e.Error == null)
    {
        string textString = (string)e.Result;

        Console.WriteLine (textString);
    }
}

Take a look at the WebClient.DownloadStringAsync Method and WebClient.DownloadFileAsync Method pages on the MSDN website for more information.

Answer 2

You cannot create a UI control on a background thread and in this case you don't need to because all of the WebBrowser methods you need are executed asynchronously anyway...

WebBrowser.Navigate

Navigate asynchronously to the document at the specified Uri.

BTW, don't forget to use Navigate method after the WebBrowser control is loaded so either use IsLoaded to check or call Navigate from Loaded event...

Answer 3

Some of the UI operations requires being invoked on the UI thread. Try

    private void bgw_DoWork(object sender, DoWorkEventArgs e)
    {
        wb.Navigated += wb_Navigated;
        wb.LoadCompleted += wb_LoadCompleted;

        wb.Dispatcher.Invoke(() =>
        {

            wb.Navigate("http://www.google.com");
        });
    }