Dr. Dobb's is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Channels ▼

Web Development

Silverlight's Validation Fix

Dan Wahlin is a Microsoft MVP and Silverlight consultant. You can contact him here.

Data validation -- the process of guaranteeing to an application that every data value is accurate -- is a crucial part of any application. But for developers using Microsoft Silverlight, this has been a problem: There wasn't a good way to ensure that data, such as a user ID or email address, is entered correctly. That's changed with Silverlight 4, thankfully.

Before now, the typical way of validating data was to throw exceptions within property-setter blocks when data was invalid. Controls bound to a property could be notified of a data validation exception by setting ValidatesOnExceptions to True in the data binding. The typical technique used for validating data was to throw exceptions within property setter blocks as data was found to be invalid. Controls bound to a property could be notified of a data validation exception by setting ValidatesOnExceptions to True in the data binding. Although this technique certainly works, there are some new options available in Silverlight 4 that can be used without resorting to throwing exceptions.

With the release of Silverlight 4 two new interfaces are now available including IDataErrorInfo and INotifyDataErrorInfo. In this article I'll walk through the process of using the IDataErrorInfo interface which provides a more simplistic way to validate data and provide end users with notifications. Let's start by taking a look at the interface's members:

public interface IDataErrorInfo
        string this[string columnName] { get; }
        string Error { get; }

The IDataErrorInfo interface only contains two members including Error which can return error information about the overall object and a default indexer property that can be used to write validation logic for different properties within an object. You'll implement the IDataErrorInfo interface on a client-side entity class in your Silverlight project such as the Person class shown in Listing 1.

public class Person : INotifyPropertyChanged, IDataErrorInfo
    public string this[string propertyName]
    public string Error
        get { …. }

Listing 1. Members of the IDataErrorInfo interface used to perform synchronous validation.

In situations where the Error property isn't used (which is often the case), you can simply return null:

public string Error
    get { return null; }

However, it can be used to return an error message detailing what's wrong with the overall object as well:

string _Errors;
const string _ErrorsText = "Error in Person data.";

public string Error
    get { return _Errors; }

Related Reading

More Insights

Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.