C#: Simple BackgroundWorker example

<Window x:Class="BackgroundWorkerExample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:BackgroundWorkerExample"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    
    <DockPanel>
        
        <DockPanel LastChildFill="True" DockPanel.Dock="Top" Margin="10">
            <Label DockPanel.Dock="Left" Width="100">URL</Label>
            <Button Name="btnGo" Click="btnGo_Click" DockPanel.Dock="Right" Width="100">Go</Button>
            <TextBox Name="tbURL"/>
        </DockPanel>
        
        <DockPanel LastChildFill="True" DockPanel.Dock="Top" Margin="10">
            <Label DockPanel.Dock="Left" Width="100">Progress</Label>
            <ProgressBar DockPanel.Dock="Bottom" Name="progBar" Value="0" />
        </DockPanel>

        <DockPanel LastChildFill="True">
            <Label DockPanel.Dock="Top">Status</Label>
            <ScrollViewer><Label Name="lblStatus" /></ScrollViewer>
        </DockPanel>
        
    </DockPanel>
    
</Window>

using System;
using System.Windows;
using System.ComponentModel;
using System.IO;

namespace BackgroundWorkerExample
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void btnGo_Click(object sender, RoutedEventArgs e)
        {
            lblStatus.Content = "";

            BackgroundWorker worker = new BackgroundWorker();

            //BackgroundWorker is event-driven. We use events to control what happens
            //during and after calculations.
            //First, we need to set up the different events.
            worker.DoWork += Worker_DoWork;
            worker.ProgressChanged += Worker_ProgressChanged;
            worker.WorkerReportsProgress = true;
            worker.RunWorkerCompleted += Worker_RunWorkerCompleted;

            //Then, we set the Worker off. 
            //This triggers the DoWork event.
            //Notice the word Async - it means that Worker gets its own thread,
            //and the main thread will carry on with its own calculations separately.
            //We can pass any data that the worker needs as a parameter.
            worker.RunWorkerAsync(tbURL.Text);
        }

        private void Worker_DoWork(object sender, DoWorkEventArgs e)
        {
            //DoWork is the most important event. It is where the actual calculations are done.

            System.Net.WebClient client = new System.Net.WebClient();

            for (int i = 0; i < 10; i++)
            {
                //We pass data to the worker using the Argument property.
                //Don't try to read data from the form directly.
                string url = (string)e.Argument;

                //download image
                byte[] imageStream = client.DownloadData(url);
                MemoryStream memoryStream = new MemoryStream(imageStream);
                System.Drawing.Image img = System.Drawing.Image.FromStream(memoryStream);

                //save image to computer
                string desktop = System.Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
                img.Save(desktop + @"\image " + i.ToString() + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg);

                //Now that the image is saved, we can update the Worker's progress.
                //We do this by going back to the Worker with a cast
                int progress = (i + 1) * 10; //Between 0-100
                ((BackgroundWorker)sender).ReportProgress(progress);
            }

            //When finished, the thread will close itself. We don't need to close or stop the thread ourselves.  
        }

        private void Worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            //This method is called whenever we call ReportProgress()
            //Note that progress is not calculated automatically. 
            //We need to calculate the progress ourselves inside Worker_DoWork.
            //This method is optional.

            lblStatus.Content += e.ProgressPercentage.ToString() + "% complete. \n";
            progBar.Value = e.ProgressPercentage;
        }

        private void Worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            //This method is optional but very useful. 
            //It is called once Worker_DoWork has finished.

            lblStatus.Content += "All images downloaded successfully.";
            progBar.Value = 0;
        }


    }
}