Is there some best practice or some recommended way how to validate forms in Silverlight? Right now I have to doall validation in endless nested if else structures and it just doesn't seem like a very reusable and maintainable way of doing this.
If I want to show error messages next to each form element I also have to create an empty text block next to each element which will hold the error in case the field is invalid.
Have a look at FluentValidation on CodePlex! It`s really comfortable to use, extend and works great with Silverlight!
I would recommand you the Silverlight toolkit, which provides easy to use dataform and entity validation mecanisms.
there are samples describing how to use it, quite a lot of blog posts and a whole (and rather interesting) MSDN magazine article
the dataform is available in the namespace xmlns:dataform="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.DataForm.Toolkit"
clearly, you need to reference the adequat assemblies in your project (for example System.Windows.Controls.Data.DataForm.Toolkit -pfiou-)
The samples provide code samples, bottom right of the samples browser there is a button which enables code view.