c# 回调委托

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Wind2
{
public partial class Form1 : Form
{
public delegate int del(int num1, int num2);
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
del a = test;
int num1 = int.Parse(this.textBox1.Text);
int num2 = int.Parse(this.textBox2.Text);
a.BeginInvoke(num1, num2,method, a);
}

public int test(int num1, int num2)
{
int sum = 0;
for (int i = num1; i <= num2; i++)
{
sum += num1;
num1++;
}
return sum;
}

public void method(IAsyncResult res)
{
if (res != null)
{
this.label1.Text=(res.AsyncState as del).EndInvoke(res).ToString();
}

}

private void Form1_Load(object sender, EventArgs e)
{
Control.CheckForIllegalCrossThreadCalls = false;
}
}
}