If you’re developing an application that uses network communications, it could be very useful, if you can validate every IPv4 address that users may enter on a form. Here’s a small code with winform application to validate both IP address, network mask addresses. I’m using 2 different regular expressions to validate these 2 different type of addresses. You’ll only need 2 TextBoxes and 2 small images (a green tick and a red cross).
You need to create 2 events for both TextBoxes: Leave and TextChanged events.
private void txbIPaddress_TextChanged(object sender, EventArgs e)
{
if (txbIPaddress.Text.Length == 0)
{
pictureBox1.Image = null;
}
else
{
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";
if (!Regex.IsMatch(txbIPaddress.Text, pattern))
{
pictureBox1.Image = Properties.Resources.delete;
}
else
{
pictureBox1.Image = Properties.Resources.tick;
}
}
}
private void txbIPaddress_Leave(object sender, EventArgs e)
{
if (txbIPaddress.Text.Length > 0)
{
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";
if (!Regex.IsMatch(txbIPaddress.Text, pattern))
{
pictureBox1.Image = Properties.Resources.delete;
MessageBox.Show("Wrong IPv4 address!", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
txbIPaddress.Select();
txbIPaddress.Text = "";
}
else
{
pictureBox1.Image = Properties.Resources.tick;
}
}
}
private void txbMask_TextChanged(object sender, EventArgs e)
{
if (txbMask.Text.Length == 0)
{
pictureBox2.Image = null;
}
else
{
string pattern = @"^(255|254|252|248|240|224|192|128|0+)\.(255|254|252|248|240|224|192|128|0+)\.(255|254|252|248|240|224|192|128|0+)\.(255|254|252|248|240|224|192|128|0+)$";
if (!Regex.IsMatch(txbMask.Text, pattern))
{
pictureBox2.Image = Properties.Resources.delete;
}
else
{
pictureBox2.Image = Properties.Resources.tick;
}
}
}
private void txbMask_Leave(object sender, EventArgs e)
{
if (txbMask.Text.Length > 0)
{
string pattern = @"^(255|254|252|248|240|224|192|128|0+)\.(255|254|252|248|240|224|192|128|0+)\.(255|254|252|248|240|224|192|128|0+)\.(255|254|252|248|240|224|192|128|0+)$";
if (!Regex.IsMatch(txbMask.Text, pattern))
{
pictureBox2.Image = Properties.Resources.delete;
MessageBox.Show("Wrong IPv4 netmask!", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
txbMask.Select();
txbMask.Text = "";
}
else
{
pictureBox2.Image = Properties.Resources.tick;
}
}
}
And here’s the result if you enter wrong IP address:
And entering wrong network mask address:
After correcting the addresses:
