Creating a BackgroundWorker
We can create the BackgroundWorker at design-time by dragging onto a Form or at run-time using the BackgroundWorker class. The following code is added when you drag a BackgroundWorker component onto a Form.
private System.ComponentModel.BackgroundWorker backgroundWorker1;
this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker();
BackgroundWorker Properties
Here is a list of BackgroundWorker class properties.
CancellationPending - Indicates if an application has requested cancellation of a BackgroundWorker.
IsBusy - Indicates if a BackgroundWorker is running an asynchronous operation.
WorkerReportsProgress - Indicates of a BackgroundWorker can report progress updates.
WorkerSupportsCancellation - Indicates if a BackgroundWorker supports asynchronous cancellation.
Methods
BackgroundWorker has two methods, RunWorkerAsync and CancelAsync. The RunWorkerAsync starts the thread and the CancelAsync stops the thread.
Events
DoWork event is the starting point for a BackgroundWorker. This event is fired when the RunWorkerAsync method is called. In this event hander, we call our code that is being processed in the background where our application is still doing some other work.
this.backgroundWorker1.DoWork += newSystem.ComponentModel.DoWorkEventHandler(this.backgroundWorker1_DoWork);
The DoWork event handler looks like this where we need to call our time-consuming method.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundProcessLogicMethod();
}
ProgressChanged event occurs when ReportProgress is called.
RunWorkerCompleted event occurs when the background operation has completed.
Working Sample
Now we are going to create a sample application. The user interface looks like Figure 1 where a Form has two Button controls and a RichTextBox control. While BackgroundWorker will be doing some background work, user can still type in the RichTextBox.
Figure 1
Start button click starts the processing BackgroundWorker and Stop button click stops the processing. While BackgroundWorker is doing work in the background, you may still type anything in the RichTextBox control.
The Start and Stop button click event handlers looks like this.
private void StartButton_Click(object sender, EventArgs e)
{
// Start BackgroundWorker
backgroundWorker1.RunWorkerAsync(2000);
}
private void StopButton_Click(object sender, EventArgs e)
{
// Cancel BackgroundWorker
if (!backgroundWorker1.IsBusy)
backgroundWorker1.CancelAsync();
}
And here is the code for the DoWork event, background worker method and WorkerCompleted event.
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker helperBW = sender as BackgroundWorker;
int arg = (int)e.Argument;
e.Result = BackgroundProcessLogicMethod(helperBW, arg);
if (helperBW.CancellationPending)
{
e.Cancel = true;
}
}
// Put all of background logic that is taking too much time
private int BackgroundProcessLogicMethod(BackgroundWorker bw, int a)
{
int result = 0;
Thread.Sleep(20000);
MessageBox.Show("I was doing some work in the background.");
return result;
}
private void backgroundWorker1_RunWorkerCompleted(object sender,
RunWorkerCompletedEventArgs e)
{
if (e.Cancelled) MessageBox.Show("Operation was canceled");
else if (e.Error != null) MessageBox.Show(e.Error.Message);
else MessageBox.Show(e.Result.ToString());
}
