在 C# 中验证 IP

Question

I was given a project to make a basic C# IPv4 address program on Windows Forms application. We are to have 5 text boxes (4 for each octet, one multiline textbox under for displaying the IP and class). In order to display the IP in the multiline textbox, I would need to first validate the numbers in all 4 textboxes (meaning all mumbers must be >= 0 and <= 255) I know there is a IPAddress.TryParse code you can use, but I am not sure how I can apply it to the 4 textboxes. Help would be very much appreciated! :)

Answer 1

In your question you write "WPF" but your screenshot is clearly a Windows Forms application so I will provide an answer for Windows Forms. However, it can easily be modified to work with WPF.

While you can validate each text box individually the interesting part of your question is how validation can be done across multiple controls. When doing validation you have to decide how the app should behave when the input is both invalid and valid. A simple and good way is to update the visual state based on the validity of the input. Eg, a button can only be clicked when the entire input is valid. This avoids the situation where the input is invalid, the user clicks the button and then gets an error that has to be dismissed. To further refine this you can provide hints in the UI about why something isn't valid.

Based on your screenshot my guess is that you want to provide some information about the result of the validation in the large text box. You can create method to update the contents of this text box based on the contents of the other text boxes. Instead of updating the large text box this method could also enable and disable buttons etc. for a more realistic scenario.

private void UpdateVisualState()
{
    var ipString = $"{textBox1.Text}.{textBox2.Text}.{textBox3.Text}.{textBox4.Text}";
    infoTextBox.Text = IPAddress.TryParse(ipString, out var address)
        ? address.ToString()
        : "(Invalid IP address)";
}

This method will take the text in textBox1 to textBox4 , create an IP address from this, parse this IP address and update infoTextBox with either the parsed IP address or a text that indicates that the IP address is invalid.

Now all you have to do is to call this method every time the text in each of the IP address octet text boxes change:

private void textBox1_TextChanged(object sender, EventArgs e)
{
    UpdateVisualState();
}

Do the same for the remaining three text boxes with IP address octets.

This a very simple way to validate the entire state of a form and as your user interface and validation rules become more complex you may find that it doesn't scale so well. However, to get started this if fine.

To learn about more advanced ways to do validation you can read User Input Validation in Windows Forms .

Answer 2

You can use LostFocus . Attach TextBox_KeyDown to all of your texboxes which you want to make validation

private void TextBox_LostFocus(object sender, RoutedEventArgs e)
{
    var textbox = (TextBox)sender;
    var isNumber = int.TryParse(textbox.Text, out var num);
    if (!isNumber)
    {
        //not validated
        return; 
    }

    if (!(num > 0 && num < 256)) 
    {
       //not validated
       return;
    }

    //valid 
}

private void TextBox_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Enter)
    {
        // call the LostFocus event to validate the TextBox
        ((TextBox)sender).RaiseEvent(new RoutedEventArgs(TextBox.LostFocusEvent));
    }
}