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Merged Resource Dictionaries provide a way to define and split resources into separate files. By locating application resources in external file we can then reuse them between applications. This feature can be helpful in custom control development, but not only.

In Silverlight 2 resources cannot be factored into separate files and that leads to large App.xaml file holding application-wide shared resources. The same problem exists while developing custom controls. All default style keys must be specified in Themes/Generic.xaml which again leads to very large file.

One major point in building line-of-business applications is the data validation. You can’t go without it and that’s where Sillverlight 3 comes in handy. In that release Microsoft added advanced facilities for validating data via two-way databinding.

Following best practices and patterns you may have heard that it is good to separate your validation logic from the UI. That’s exactly the case with the built-in validation in Silverlight.

Let’s start with an example of a data form containing validation logic.

Silverlight 3 was just announced on MIX09 – I’m sure you are all pretty excited about the new features included in this release. There is a lot to talk about – offline support, styling, binding, controls, media, animation, graphics, etc.

This article aims to give you a brief overview of the new features as well as links to in-depth articles explaining the details.

Let’s start by organizing the new features in groups:

DataBinding

• Element to Element Binding – enables property binding to CLR objects and other UI components via XAML.

Introduction

When it comes to making calls to a Web Service in Silverlight you have no other way, but to do it async. In many scenarios this could be a problem and especially when you use data binding.

The Problem

Consider you have a business objects Merchant and Sale and the Merchant has property Sales of type List as shown on the class diagram.

The sales are loaded from a web service.

What is a Pivot table/grid? According to Wikipedia it is a data summarization tool found in spreadsheet applications. Still when I was a child I learned that people understand the best when they see an example.

Consider you have a table that contains the nutrition of given food, say a pizza:

In the data above you see that every nutrition is contained in a specific Group - 3 groups and 21 nutrition in total.

A common scenario in data binding is to format the data displayed in the UI. Almost every time you show a date or a price you need to format it. Silverlight and WPF are using the so called converters to apply custom logic to a binding.

Using Converters

Let's make a small example that illustrates the problem. Consider a ListBox filled with client details - name and birthdate.

Here the ListBox is bound to a custom business object with a field Birthdate of type DateTime - pretty common situation.

Yesterday we've published Silvester - Silverlight Twitter widget and the idea was to let people put it on their blogs. To use the widget you need only an HTML snippet placed somewhere on your blog/profile page. The snippet contains an <object> tag that refers the widget's XAP file from our domain. So what you actually do is refer a resource from other domain, a.k.a x-domain scenario or cross-domain scenario.

Silverlight is a client technology and as such it sets a lot security requirements to keep the applications secure by default.

Are you a fan of Twitter? Personally I'm, but I'm also a fan of Silverlight. Twitter has a couple of Flash and HTML badges (a.k.a widgets) you can get and put on your blog to let your visitors know what you are up to in the moment. However, Twitter does not have a Silverlight widget. What negligence! :) If you are like me and want not a Flash, but a Silverlight widget on your blog go ahead and read on how you can build one by yourself or just copy the text below to use it.

I've been playing with some timers and Web Services and I got stuck in a case where the background thread was trying to update the UI. Well, that's never going to happen. To update the UI you should use the UI thread. Let's see how we can call the UI thread from the background thread.

Consider this situation:

You have data that needs to be updated every minute. The data is loaded by calling a web service.

For the update you can use the Timer class. Both the timer and the web service calls are executed asynchronously.