// number only textbox using TryParse
private void textBox1_KeyPress(object
sender, KeyPressEventArgs e)
{
    int value = 0;
    e.Handled = !int.TryParse(e.KeyChar.ToString(), out value);
}

// number only textbox using Regex.IsMatch
private void
textBox2_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!System.Text.RegularExpressions.Regex.IsMatch(e.KeyChar.ToString(), “\\d+”))
        e.Handled = true;
}

// NumberTextBoxLib custom control (inherited from TextBox)
public
partial class NumberTextBox : TextBox
{
        public NumberTextBox()
        {
            InitializeComponent();
        }

        protected override void OnKeyPress(KeyPressEventArgs e)
        {
            base.OnKeyPress(e);
            int value = 0;
            e.Handled = !int.TryParse(e.KeyChar.ToString(), out value);
   
    }
}