C# - Limit value in Textbox

Question

Hi, I’m wearing C#, and I’m having some trouble using a Textbox. I have a Textbox with this format: 192.168.100.1, to be more specific I’m putting IP numbers.

I would like from the second . (100) the number was not greater than 255

I have tried using Substring and Length, but the bug program. Can someone help me???

Answer 1

Suggestion 1

I recommend you use the component NumericUpDown. Include four of them in your form and seven properties minimum for 0 and maximum to 255.

The advantage of using this type of component is that you have control over the numbers you will receive, and you are sure that you will only receive numbers.

Suggestion 2

Use the component MaskedTextBox. Change the property mask for '999.999.999.999' and the property SkipLiterals for false.

To check the entered value, use the function:

    public static int verificaValor(string ip, int parte)
    {
//ip é o texto com o ip
//parte é qual das quatro partes você quer verificar
        if (parte == 1)
            return int.Parse(ip.Substring(0, 3));
        if (parte == 2)
            return int.Parse(ip.Substring(4, 3));
        if (parte == 3)
            return int.Parse(ip.Substring(8, 3));
        if (parte == 4)
            return int.Parse(ip.Substring(12, 3));
    }

This function will return the value of one of the 4 parts of ip, e.g.:

If ip is 192.168.100.1 and you use verificaValor(textBoxIp.text, 3); 100 will be returned.

So you can check the value using an if:

if (verificaValor(textBoxIp.text, 3) > 255)
    //mensagem de erro

Even so, I suggest the first way to do, as it prevents the user to enter values above what you want.