Monday, November 08, 2004

BackgroundWorker Component in Windows Forms 2.0

In Windows Forms applications, the "UI Thread Only" rule states that developers should avoid writing code that directly manipulates controls on the UI thread from a worker thread except using Control.XXXInvoke. In .NET framework 1.x, writing code dealing with the communication between the UI thread and a worker thread requires a fair degree of work.

In .NET framework 2.0, Microsoft will introduce a new component named BackgroundWorker to save time for developers to write this communication code.

Below is a sample I created to show you how easy to use BackgroundWorker. I created a Windows Forms application with VS 2005 beta, drag and drop two buttons, a BackgroundWorker, and a ProcessBar control on the Window.

namespace TestBackgroundWorker
{
partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
progressBar1.Maximum = 100;
}
private void button1_Click(object sender, EventArgs e)
{
progressBar1.Value = 0;
backgroundWorker1.RunWorkerAsync();
}
private void button2_Click(object sender, EventArgs e)
{
backgroundWorker1.CancelAsync();
}

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
// This method will run on a thread other than the UI thread.
// Be sure not to manipulate any Windows Forms controls created
// on the UI thread from this method.
Thread.Sleep(10000);
if (backgroundWorker1.CancellationPending)
{
e.Cancel = true;
return;
}
backgroundWorker1.ReportProgress(50);
Thread.Sleep(10000);
}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = e.ProgressPercentage;
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if(e.Cancelled)
progressBar1.Value = 80;
else
progressBar1.Value = 100;
}
}
}


I learnt the BackgroundWorker component from Michael Weinhardt's article

Safe, Even Simpler Multithreading in Windows Forms 2.0

The link seems to be broken now.

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