using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
 
namespace WindowsFormsApplication1
{
    public partial class ClassA : Form
    {
        private ClassB B = new ClassB();
 
        public ClassA()
        {
            InitializeComponent();
            button1.Click += (s, e) => B.button1_Click_1(s, e);
            // button1.Click += (s, e) => B.button1_Click_2((Button)s, "hogehoge");
        }
    }
 
    public class ClassB
    {
        public void button1_Click_1(object sender, EventArgs e)
        {
            (Button)sender.Text = "hogehoge";
        }
        
        public void button1_Click_2(Button button, string arg /* arg2,arg3... */)
        {
            button.Text = arg;
        }
    }
}