ASP MVC : The validation method is not working !

[arao]

In URL ASP.NET/LEARN/MVC/Tutorial-28-cs.aspx

The code compiles, but at run time I get NULL Reference in FirstName .

The code is as follows:

protected void ValidateContact(Contact contactToValidate)
        {
            if (contactToValidate.FirstName.Trim().Length == 0)
                ModelState.AddModelError("FirstName", "First name is required.");
            if (contactToValidate.LastName.Trim().Length == 0)
                ModelState.AddModelError("LastName", "Last name is required.");
            if (contactToValidate.Phone.Length > 0 && !Regex.IsMatch(contactToValidate.Phone, @"((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}"))
                ModelState.AddModelError("Phone", "Invalid phone number.");
            if (contactToValidate.Email.Length > 0 && !Regex.IsMatch(contactToValidate.Email, @"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$"))
                ModelState.AddModelError("Email", "Invalid email address.");
        }

[tlhintoq]

If you pass in a Contact object with none of the values set then yeah, they are null.

contactToValidate.FirstName.Trim().Length

You can't Trim() or get the length of a null.
You need to check if your object is null before trying to perform actions on it.
You should also make sure that your default constructor for the Contact object assigns actual values to variables.

"How do I fix a 'object reference not set to an instance of an object' error?

The line your code stopped on while debugging holds all your answers.
One of the variables/objects was created but not initialized. For example:

string TempString;// Created but not initialized so this is still null
//versus
string TempString = string.empty;

Debug your project again. This time, when it breaks on a line look at the Locals pallet to see which variable/object is null. You can also hover your mouse over each variable and the hothelp will shows its value. One of them will be null.