Do you use field and list item validation (in 2010)

<introEmbed
  body={<>
```csharp
class CreateShoppingListHandler : SPItemEventReceiver
{
    public override void ItemAdding(SPItemEventProperties properties)
    {
        float price = 0;
        float cost = 0;

        if(float.TryParse(properties.ListItem.Fields["Price"].ToString(), out price) && float.TryParse(properties.ListItem.Fields["Cost"].ToString(), out cost))
        {
            if(price < cost)
            {
                properties.ErrorMessage = "The cost must not be less than the price";
                properties.Cancel = true;
            }
        }
    }
}
```

**Bad example: using custom code – creating a custom event receiver on the item (the item adding event or item updating event)**
  </>}
/>

<imageEmbed
  alt="Image"
  size="large"
  showBorder={false}
  figureEmbed={ {
    preset: "goodExample",
    figure: "Good example: using no code – just using the field validation on a list. A demo of this from Andrew Connell on http://channel9.msdn.com/learn/courses/SharePoint2010Developer/ListsAndSchemas/FieldandListItemValidation/",
    shouldDisplay: true
  } }
  src="/uploads/rules/do-you-use-field-and-list-item-validation-in-2010/ListValidation.jpg"
/>