IPTextBox

//https://stackoverflow.com/a/60781845/10216583

using System;
using System.Linq;
using System.Windows.Forms;
using System.ComponentModel;

namespace JQSOFT
{
    [DesignerCategory("Code")]
    class IPTextBox : TextBox
    {
        #region Constructors

        public IPTextBox() : base() { }

        #endregion

        #region Public Properties

        [Browsable(false)]
        public bool IsValidIP { get { return IsValidInput(true); } }

        #endregion

        #region Private Methods

        private bool IsValidIP4Part(string input)
        {
            int y;
            return input.Length > 1 && input.StartsWith("0") ? false
                : int.TryParse(input, out y) && y < 256;
        }

        private bool IsValidInput(bool full = false)
        {
            int y;
            var split = Text.Split('.');
            var parts = split.Where(x => int.TryParse(x, out y));

            return !Text.StartsWith(".") &&
                !Text.EndsWith("..") &&
                split.Length < 5 &&
                parts.All(x => IsValidIP4Part(x));
        }

        #endregion

        #region Base

        protected override void OnTextChanged(EventArgs e)
        {
            base.OnTextChanged(e);

            if (!IsValidInput())
            {
                SendKeys.SendWait("{BS}");
                OnInvalidInput();
            }
        }

        protected override void OnKeyPress(KeyPressEventArgs e)
        {
            base.OnKeyPress(e);

            if (!char.IsControl(e.KeyChar) &&
                !char.IsDigit(e.KeyChar) &&
                e.KeyChar != '.')
            {
                e.Handled = true;
                OnInvalidInput();
            }
        }

        #endregion

        #region Custom Events

        public event EventHandler InvalidInput;

        protected virtual void OnInvalidInput()
        {
            var h = InvalidInput;
            h?.Invoke(this, EventArgs.Empty);
        }

        #endregion
    }
}