What is the best practice for constructor parameter validation? Suppose a simple

Question

What is the best practice for constructor parameter validation?

Suppose a simple bit of C#:

public class MyClass
{
    public MyClass(string text)
    {
        if (String.IsNullOrEmpty(text))
            throw new ArgumentException("Text cannot be empty");

        // continue with normal construction
    }
}
Would it be acceptable to throw an exception?

The alternative I encountered was pre-validation, before instantiating:

public class CallingClass
{
    public MyClass MakeMyClass(string text)
    {
        if (String.IsNullOrEmpty(text))
        {
            MessageBox.Show("Text cannot be empty");
            return null;
        }
        else
        {
            return new MyClass(text);
        }
    }
}

Explanation / Answer

I tend to perform all of my validation in the constructor. This is a must because I almost always create immutable objects. For your specific case I think this is acceptable.

if (string.IsNullOrEmpty(text))
throw new ArgumentException("message", "text");
If you are using .NET 4 you can do this. Of course this depends on whether you consider a string that contains only white space to be invalid.

if (string.IsNullOrWhiteSpace(text))
throw new ArgumentException("message", "text");

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