ASP.NET 4 Unleashed

Using Page.IsValid

As previously mentioned, you should always check the Page.IsValid property when working with data submitted with a form that contains validation controls. Each of the validation controls includes an IsValid property that returns the value True when a validation error doesn’t exist. The Page.IsValid property returns the value True when the IsValid property for of the validation controls in a page returns the value True.

It is easy to forget to check the Page.IsValid property. When you use a browser that supports JavaScript with the validation controls, you are prevented from submitting a form back to the server when validation errors exist. However, if someone requests a page using a browser that does not support JavaScript, ...