Method argument validation of complex types

Question

I'm a fan of argument validation in methods. Something like this is commonly seen in my code:

public void Foo(string someString)
{
    #region parameter validation
    if(string.IsNullOrWhiteSpace(someString))
        throw new ArgumentNullException("someString");
        // Let's ignore the .NET 4.6 nameof-feature for the sake of this question.
    #endregion

    // do things
}

Now let's say the method doesn't accept a string, but a complex object. Let's say I want the method to validate whether a property of this complex object is set. What would be the correct way to do this? Up until now I've done it like this:

public void Foo(Person person)
{
    #region parameter validation
    if(person == null)
        throw new ArgumentNullException("person");
    if(string.IsNullOrWhiteSpace(person.Name))
        throw new ArgumentNullException("person.Name");
    #endregion

    // do things
}

Is there some best practice for this? Is ArgumentNullException the correct way to go? Is checking properties like this even recommended?

Answer 1

In my case, all my models have a Validate method, this way I just call it and if it returns false (which means I got errors) I call another method to get the errors from it and display to the user, something like this:

if (person == null)
    throw new ArgumentNullException (nameof (person));

// Validates only 1 property.
if (!person.Validate (nameof (person.MyProperty)))
    DisplayErrors (person);

// Validates all properties.
if (!person.Validate ())
    DisplayErrors (person);

The reason behind it is that in most cases I have to allow the model to be invalid while the user is filling the information. I use these method with the interface INotifyDataErrorInfo for WPF to enable the UI to refresh when errors occur.

When only part of object is required for a method or operation, a facade model is the solution where you create a new class that envelopes your more complex one, and the facade class have the Validate method too to do partial validation.