Structured code for limiting what values you can set for a property

Question

What would be the correct (and best) way to code in limits as to what values a property can get?

For example, suppose I have the following simple class:

Public Class MyClass
   Public Property MyDate As Date

Now, suppose MyDate gets set at run-time, but can't take any values less than a year ago.

Is it correct to throw an exception in the MyDate's setter and then program this in my main module in a Try...Catch fashion and then alert the user if the value is bad or is there a better way to do this?

I'm sure this is a stupidly simple question, but I just want to make sure I'm doing this according to best programming practices.

Answer 1

While throwing an exception is a valid option, I recommend against it. The reason is that when a programmer sets a property he/she expects very little to happen other than the value being set. In this case I'd recommend using a set function instead of a property or having the value passed as part of the constructor (where programmers expect validation logic of this sort to happen).

Answer 2

Check this article out. It gives an overview of Validators in the System.ComponentModel.DataAnnotations namespace. They are attributes for your model that support validation.

http://stephenwalther.com/archive/2008/09/10/asp-net-mvc-tip-43-use-data-annotation-validators.aspx

ASP.NET MVC supports surfacing those validations on forms using JS, but in other applications types you can read the attributes from the model itself and enforce the validations.

Answer 3

Yes, throwing and exception is a good idea. ArgumentOutOfRangeException seems to be the best in that situation. Following the MSDN:

The exception that is thrown when the value of an argument is outside the allowable range of values as defined by the invoked method.