Background Worker - Complete Explanation

As requested by a commenter/follower of the blog, I created an example which explains all most all the processes related to the Background worker in .Net. The processes from A - Z is explained as follows,

• Add a Background worker to the project

To add a background worker to the form you need, drag & drop the component from the Toolbox under the Components section.

• Allow to Report Current progress or Cancel the background operation

Set the WorkerReportsProgress and WorkerSupportsCancellation properties to "True" in-order to allow the Background worker to allow Report current progress or Cancel the current operation.

• Adding the DoWork, ProgressChanged and RunWorkerCompleted methods

DoWork method should include the background operation you intend to perform. In order to add this method you can select the background worker, go to events of it and double click on the DoWork. Using the same mechanism ProgressChanged and RunWorkerCompleted methods can be added as well.

• Implement the added methods

In the example I've composed the DoWork method includes a loop which runs from 0 to 100. Also while the loop is running it is stopped for 100 milliseconds at each iteration. The code segment is as follows,

private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e) 
{
     BackgroundWorker backWorker = sender as BackgroundWorker;
     for (int i = 1; i <= 100; i++)
     {
         // Check wether the user has requested a cancellation,
         // before processing further
          if (!backWorker.CancellationPending)
          {
              // Wait 100 milliseconds
              Thread.Sleep(100);
              // Reports progress
              backgroundWorker.ReportProgress(i);
          }
          else
              e.Cancel = true;
      } 
}

As seen on the above code segment, before continuing with each iteration it is checked the user has requested for a cancellation. If so, the loop will be terminated. Also the current progress of the background worker is reported. Then according to the reported work progress, UI can be updated using the ProgressChanged method as seen from the code below. I've updated the value of the progress bar and a label displaying the current completed percentage.

 private void backgroundWorker_ProgressChanged(object sender,
            ProgressChangedEventArgs e) 
{
    // Setting the Progress bar value and updating the label
    progressBar.Value = e.ProgressPercentage;
    lblProgress.Text = string.Format(processingText,
            e.ProgressPercentage.ToString()); 
}

After Completing or Cancelling the background process, RunWorkerCompleted method will be executed which contains the finalizing section of the background process. In this method you can perform a check whether the process is cancelled or completed successfully and updated the UI accordingly. Sample code is as follows,

private void backgroundWorker_RunWorkerCompleted(object sender,
            RunWorkerCompletedEventArgs e) 
{
    // Checks wether the background process is cancelled
    if (e.Cancelled)
          lblProgress.Text = processCancelled;
    else
          lblProgress.Text = processCompleted;

     progressBar.Value = 0;
     errorProvider.Dispose();
}

After creating all the required methods all you need is to invoke the Background worker when needed. The invoking can be done as follows. A check is performed to see whether the background worker is busy or not before invoking which is a very important step.

private void btnPerfromBackOp_Click(object sender, EventArgs e) 
{
    // Checks if the Background worker is busy before giving a wake up call to it
    if (!backgroundWorker.IsBusy)
    {
         //starts the background operation
         backgroundWorker.RunWorkerAsync();
     }
     else
      errorProvider.SetError(progressBar, backgroundWorkerBusy); 
}

The user is able to terminate a background process as well. To perform this the following code can be used in an event as desired. In this example I've used a button click event.

private void btnCancel_Click(object sender, EventArgs e) 
{
    if (backgroundWorker.WorkerSupportsCancellation)
    {
        // Requests the background process to stop
        backgroundWorker.CancelAsync();
     } 
}

The following image displays the UI created for the above used example.

To download the sample follow the link below.
Background Worker Sample

Hope this post solves problems you have related to the Background worker. !!!