Three dots in textbox

Question

I have a textbox C# for IP addressing; validating IP address. However, I'm trying to limit to numbers and the amount of dots a user can enter in for the IP address. This way it limits errors.

Seems I'm able to enter one dot, I would like to increase that number to three. I can create a "Regex.IsMatch" and validate using "IPAddress", but I'm just trying to limit what the user can enter before pressing a button to proceed.

Is there a way to do this? Searching the Internet haven't found any way to do this.

    string pattern = @"\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b";
    bool CKDots = Regex.IsMatch(TracertIP, pattern);

    private void txtTracerouteIP_KeyPress(object sender, KeyPressEventArgs e)
    {
        // Enter only numbers.
        if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.'))
        {
            e.Handled = true;
        }
        // Only one dot, but I need three.
        //if ((e.KeyChar == '.') && ((sender as TextBox).Text.IndexOf('.') > -1))
        //{
        //    e.Handled = true;
        //}
    }

Answer 1

Since the MaskedTextBox is not an option and you prefer the TextBox, then maybe this would lead to something.

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

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

        public IPTextBox() : base() { }

        #endregion

        #region Public Properties

        [Browsable(false)]
        public bool IsValidIP => IsValidInput(Text, true);

        #endregion

        #region Private Methods

        private bool IsValidInput() => IsValidInput(Text);

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

            return !input.StartsWith(".")
                && !input.EndsWith("..")
                && !split.Any(x => x.Length > 1 && x.StartsWith("0"))
                && (full ? parts.Count() == 4 : split.Count() < 5)
                && parts.All(x => int.Parse(x) < 256);
        }

        #endregion

        #region Base

        protected override void OnTextChanged(EventArgs e)
        {
            if (Text.Trim().Length > 0 && !IsValidInput())
            {
                SendKeys.SendWait("{BS}");
                OnInvalidInput();
            }
            else
                base.OnTextChanged(e);
        }

        protected override void OnKeyPress(KeyPressEventArgs e)
        {           
            if (!char.IsControl(e.KeyChar)
                && !char.IsDigit(e.KeyChar)
                && e.KeyChar != '.')
            {
                e.Handled = true;
                OnInvalidInput();
            }
            else
                base.OnKeyPress(e);
        }

        private const int WM_PASTE = 0x0302;        

        protected override void WndProc(ref Message m)
        {
            switch (m.Msg)
            {
                case WM_PASTE:
                    if (!IsValidInput(Clipboard.GetText()))
                        return;
                    break;
                default:
                    break;
            }
            base.WndProc(ref m);
        }

        #endregion

        #region Custom Events

        public event EventHandler InvalidInput;

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

        #endregion
    }
}

Steps & Description

---

• Derive a new class from TextBox control.

• Override the OnKeyPress method to permit the control, digit, and . keys only.

• Override the OnTextChanged method to validate the modified text thru the IsValidInput function and delete the last entered character if the function returns false.

• The IsValidInput function checks whether the entered text can produce a valid IP address or a part of it.

• The IsValidIP read-only property returns whether the text is a valid IP address. As you know, the IPAddress.TryParse(..) will also return true if you pass for example 1 or 192.168 because it parses them as 0.0.0.1 and 192.0.0.168 respectively. So it won't help here.

• The custom event InvalidInput is raised whenever an invalid key is pressed and if the Text does not form a valid IP address or a part of it. So, the event can be handled in the implementation to alert the user if necessary.

That's it all.

Related

---

▶ How to TextBox inputs of custom format?

Answer 2

We can keep it simple and use the validating event:

    this.txtTracerouteIP.Validating += this.txtTracerouteIP_Validating;

And then:

    string pattern = @"^\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b$";

    private void txtTracerouteIP_Validating(object sender, CancelEventArgs e)
    {
        if (!Regex.IsMatch(txtTracerouteIP.Text, pattern))
        {
            MessageBox.Show("IP Address must be in the format '255.255.255.255'!");
            txtTracerouteIP.SelectAll();
            e.Cancel = true;
        }
    }