void UpdateLabel2(string message)
{
 this.Invoke((EventHandler)delegate{ this.label1.Text = message;});
}

private void button2_Click(object sender, EventArgs e)
{
Thread thread1 = new Thread(new ParameterizedThreadStart(UpdateLabel2));
thread1.Start("更新Label");
}

private void UpdateLabel2(object str)
{
if (label2.InvokeRequired)
{
// 当一个控件的InvokeRequired属性值为真时，说明有一个创建它以外的线程想访问它
Action<string> actionDelegate = (x) => { this.label2.Text = x.ToString(); };
// 或者
// Action<string> actionDelegate = delegate(string txt) { this.label2.Text = txt; };
this.label2.Invoke(actionDelegate, str);
}
else
{
this.label2.Text = str.ToString();
}
}

private void button4_Click(object sender, EventArgs e)
{
using (BackgroundWorker bw = new BackgroundWorker())
{
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.RunWorkerAsync("Tank");
} 
}
void bw_DoWork(object sender, DoWorkEventArgs e)
{ 
// 这里是后台线程， 是在另一个线程上完成的， 这里是真正做事的工作线程
// 可以在这里做一些费时的，复杂的操作
Thread.Sleep(5000);
e.Result = e.Argument + "工作线程完成";
}
void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
//这时后台线程已经完成，并返回了主线程，所以可以直接使用UI控件了 
this.label4.Text = e.Result.ToString(); 
}