How to write an Event without using visual studio (in .cs or simply a .txt file)

I'm trying to write a Enter Event for TB1 (textbox)

This code for Form1 (in Form1.cs) , would normally write it with the help of Designer:

    using System;
    using System.Windows.Forms;
    namespace Project1
    {
            // aqui seria o método para o evento Enter que eu queria, o que está abaixo representado
            // para que a letra 'text' desapareça              

        private void TB1_Enter(object sender, EventArgs e)
            {
                if(TB1.Text=="Text")
                {
                    TB1.Text="";
                }
            }
     }

In the code below I wanted to implement the above event. What I was going to want to know is if I could write the event in the below file so that it can be compiled later. >

        using System;
        using.System.Windows.Forms;
        using System.Runtime.InteropServices;
    namespace Project1
    {
    [ComVisible(true)]
        public class EventArgs
        {
            //
            //Summary:
            //provides a value to use with events that do not have event data
            public static readonly EventArgs Empty;

            //
            //Summary:
            //Initializes a new instance of the System.EventArgs class
            public EventArgs()
            {

            }
        }
            public class Form1:Form
            {
                public static void Main()
                {
                     AplicationEnableVisualStyles();
                     Aplication.Run(new Form1());
                }
                public Form1()
                {
                    //textBox1
                  TextBox TB1 = new TextBox();
                TB1.Location = new Point(30, 20);
                TB1.Size = new Size(100, 30);
                TB1.Text = "Text";
                    //add control to textBox
                    this.Controls.Add(TB1);
                }
           }
     }