I’ve been using Silverlight 3 heavily for the past few months, and during that time have discovered many things to love and hate.  One problem I faced with Silverlight 3 (that I should have blogged about earlier) is something I think many developers may have faced.  In the application I’ve been working on, we’ve broken up our functionality into “partial views” (we’re using MVVM) by encapsulating logic into Silverlight UserControls.  Well with this approach, we ran into an interesting binding problem.

Let’s say you have a UserControl, and that UserControl exposes a DependencyProperty.  Then within the UserControls content, you try to bind a control to that Dependency Property.  Well there’s an interesting issue with that approach in Silverlight 3.  Let’s look at a very simple example and see where the problem exhibits itself.

In this example, we’ll be creating a totally useless application to illustrate the point.  We’ll have a Page (MainPage.xaml), and one UserControl (MyControl.xaml).  The UserControl will consist of a single string property called MyText and the goal is to get that property’s value to be displayed in a TextBlock (which is within the UserControl).  We’ll then add that UserControl to the page, and we’ll dynamically set MyText on the UserControl.  Simple setup, right?  What can go wrong? Well, let’s get started.

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I’ve been lucky enough to work on a new project for a client involving Silverlight 3 and the Silverlight Virtual Earth CTP.  One reoccurring issue that keeps coming up is performance, and I’m always looking for ways to balance functionality with speed.  In the app we are loading up a Virtual Earth map and populating it with data (nothing new).  We have a fair amount of data being loaded for various functions and layers.  Users are able to show and hide layers as well as interact with the map’s basic functions (zoom, pan, etc).  Users can then navigate to other areas based on selections from the map page. 

Since we’re using SL3, we’re using the Navigation Framework to navigate between “pages.”  If you’re not familiar with the Navigation Framework, check out Martin Mihaylov’s article, or if you prefer videos, be sure to check out Tim Heuer’s video on the topic.  Now let’s move on to the problem, and a solution…

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