ArgumentException or ArgumentNullException for string parameters?

Question

Far as best practices are concerned, which is better:

public void SomeMethod(string str) 
{
    if(string.IsNullOrEmpty(str))
    {
        throw new ArgumentException("str cannot be null or empty.");
    }

    // do other stuff
}

or

public void SomeMethod(string str) 
{
    if(str == null) 
    {
        throw new ArgumentNullException("str");
    }

    if(str == string.Empty)
    {
        throw new ArgumentException("str cannot be empty.");
    }

    // do other stuff
}

The second version seems more precise, but also more cumbersome than the first. I usually go with #1, but figured I'd check if there's an argument to be made for #2.

Answer 1

I would suggest using the first one. If your method doesn't expects null or empty string it really doesn't matter if null or empty was passed - important to report and error and that is what 1st variant does.

Answer 2

I'd say the second way is indeed more precise - yes, it's more cumbersome but you can always wrap it in a method to avoid having to do it all the time. It could even be an extension method:

str.ThrowIfNullOrEmpty("str");


public static void ThrowIfNullOrEmpty(this string value, string name)
{
    if (value == null)
    {
        throw new ArgumentNullException(name);
    }
    if (value == "")
    {
        throw new ArgumentException("Argument must not be the empty string.",
                                    name);
    }
}

Another form which is potentially useful is one which returns the original string if everything is okay. You could write something like this:

public Person(string name)
{
    this.name = name.CheckNotEmpty();
}

Another option to consider is using Code Contracts as an alternative to throwing your own exceptions.