How To Use BackgroundWorker in C#

Introduction

BackgroundWorker is the class in System.ComponentModel which is used when you need to do some task on the back-end or in different thread while keeping the UI available to users (not freezing the user) and at the same time, reporting the progress of the same.

Using the Code

Backgroundworker has three event handlers which basically takes care of everything one needs to make it work.

1. DoWork - Your actual background work goes in here
2. ProgressChanged - When there is a progress in the background work
3. RunWorkerCompleted - Gets called when background worker has completed the work.

I have created a sample WPF application which demonstrates how to use the background worker in C#.

<ProgressBar x:Name="progressbar"
 HorizontalAlignment="Left" Height="14"
 Margin="191,74,0,0" VerticalAlignment="Top"
 Width="133"/>
<Button x:Name="button" Content="Button"
 HorizontalAlignment="Left"
 Margin="249,97,0,0" VerticalAlignment="Top"
 Width="75" Click="button_Click"/>

On Window initialization, I am creating a new object of BackgroundWorker and registering the event handlers for the same.

BackgroundWorker bg;
public MainWindow()
{
InitializeComponent();
bg = new BackgroundWorker();
bg.DoWork += Bg_DoWork;
bg.ProgressChanged += Bg_ProgressChanged;
bg.RunWorkerCompleted += Bg_RunWorkerCompleted;
bg.WorkerReportsProgress = true;
}

Here is the implementation of all three event handlers.

private void Bg_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
MessageBox.Show("Task completed");
}

private void Bg_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressbar.Value += 1;
//label.Content = e.ProgressPercentage;
}

private void Bg_DoWork(object sender, DoWorkEventArgs e)
{
for (int i = 1; i <= 10; i++)
{
Thread.Sleep(1000); //do some task
bg.ReportProgress(0);
}
}

In order to make this stuff work, you need to trigger the DoWork event and for that, I am using button click event.

private void button_Click(object sender, RoutedEventArgs e)
   {
           progressbar.Value = 0;
           progressbar.Maximum = 10;
           bg.RunWorkerAsync();
   }

It is a very basic example of background worker, but it is good to start with.

One must be wondering how it is updating the progress bar if it is working in the background.

Well, the ProgressChanged event handler runs on UI thread whereas DoWork runs on application thread pool. That's why despite running in the background on different thread, it is not freezing the UI and updating the progressbar upon making progress.

Please leave your comments for any question or concerns.

Points of Interest

It is really helpful to understand how background worker is useful - especially when one needs to do some task like parallel processing or sending bulk emails or transaction and keeping the UI available to user and notifying the progress.

History

• 24^th July, 2016: Initial version