c#中子线程控制进度条的一个简单例子

这个问题来自社区提问，代码保留一份用来以后回答

using System;
using System.ComponentModel;
using System.Windows.Forms;
namespace WindowsApplication4
... {
/**/ /// <summary>
/// gui类
/// </summary>
public partial class Form1:Form
... {
public Form1()
... {
InitializeComponent();
}
private void button1_Click( object sender,EventArgse)
... {
// 用子线程工作
new System.Threading.Thread( new System.Threading.ThreadStart(StartDownload)).Start();
}
// 开始下载
public void StartDownload()
... {
Downloaderdownloader = new Downloader();
downloader.onDownLoadProgress += new Downloader.dDownloadProgress(downloader_onDownLoadProgress);
downloader.Start();
}
// 同步更新ui
void downloader_onDownLoadProgress( long total, long current)
... {
if ( this .InvokeRequired)
... {
this .Invoke( new Downloader.dDownloadProgress(downloader_onDownLoadProgress), new object [] ... {total,current} );
}
else
... {
this .progressBar1.Maximum = ( int )total;
this .progressBar1.Value = ( int )current;
}
}
}

/**/ /// <summary>
/// 下载类
/// </summary>
public class Downloader
... {
// 委托
public delegate void dDownloadProgress( long total, long current);
// 事件
public event dDownloadProgressonDownLoadProgress;
// 开始模拟工作
public void Start()
... {
for ( int i = 0 ;i < 100 ;i ++ )
... {
if (onDownLoadProgress != null )
onDownLoadProgress( 100 ,i);
System.Threading.Thread.Sleep( 100 );
}
}
}
}