Throw an error when the user enter null or empty string

Question

I\'m attempting to resolve the following exercise:

You need to create a class named Product that represents a product. The class has a

Answer 1

Your if state is wrong. Let's do a truth table:

if (value != String.Empty || value != null)

---

Name = null   True Or False  = True 
Name = "name" True Or True = True
Name = ""     False Or True = True 

Your if statement is always true!

I would re-write it thus:

if (value == String.Empty || value == null)
{
     throw new ArgumentException("Name cannot be null or empty string", "Name");  
}
else
{
     name = value;
}

---

you could just change the Or to and AND but I think the above reads better (the below has an unnecessary double negative):

if (value != String.Empty && value != null)
{
   name = value;
}
else
{
    throw new ArgumentException("Name cannot be null or empty string", "value");
}

---

As Dmitry Bychenko says, I didn't notice you were not testing for value. In getters you should use the value property. Not the name of your property

---

The second parameter (again pointed out by Dmitry Bychenko) in your exception should be:

The name of the parameter that caused the current exception.

MSDN

which in your case is the string "value":

throw new ArgumentException("Name cannot be null or empty string", "value");

Answer 2

Use String.IsNullOrEmpty Method (String). Change your set like this:

set
{
      if (!string.IsNullOrEmpty(value))
      {
            name = value;
      }
      else
      {
            throw new ArgumentException("Name cannot be null or empty string", "value");
      }
}

Also you can use String.IsNullOrWhiteSpace Method (String) that Indicates whether a specified string is null, empty, or consists only of white-space characters.

Answer 3

If you want different exceptions on null and on empty string (often null means that something is totally wrong, when empty string is just a format error):

public string Name {
  get {
    return name;
  }
  set {
    if (null == value)
      throw new AgrumentNullException("value");
    else if (String.Equals(value, ""))
      throw new AgrumentException("Empty values are not allowed.", "value");

    name = value; 
  }
}

In case you don't want to distiguish them:

public string Name {
  get {
    return name;
  }
  set {
    if (String.IsNullOrEmpty(value))
      throw new AgrumentException("Null or empty values are not allowed.", "value");

    name = value; 
  }
}

Note, that in both cases it's value that you have to test, not a property Name. In your original code the name's (and so Name as well) initial value is null and you'll get exception whatever you try to set.