a textBox class : when press any key show it

As already pointed out in Solution 1 by OriginalGriff, showing a MessageBox every time a key is pressed makes it very difficult to type the text in TextBox. Instead create a Label and show the key pressed on that Label as shown below:

using System;
using System.Windows.Forms;
using System.Drawing;

namespace KeyPressDisplayTextBox {
    public partial class Form1 : Form {
        private TextBox textBox1;
        private Label label1;

        public Form1() {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e) {
            textBox1 = new TextBox();
            textBox1.Location = new Point(10,10);
            textBox1.KeyPress += textBox1_KeyPress;
            Controls.Add(textBox1);

            label1 = new Label();
            label1.Location = new Point(10, 40);
            label1.BorderStyle = BorderStyle.FixedSingle;
            label1.Font = new Font("Arial", 14);
            Controls.Add(label1);
        }

        void textBox1_KeyPress(object sender, KeyPressEventArgs e) {
            label1.Text = e.KeyChar.ToString();
        }
    }
}

To run the above code, create a Windows Forms application in C# with the name KeyPressDisplayTextBox , double click on Form1 in the designer window which opens the code file, then replace the contents of Form1.cs with the above code and run the application.