Silverlight 4 : YouTube – Standard Feed, Search and Play videos – Tip of the day


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YouTube is the most popular and largest video sharing website on which users can upload, view and share videos.  One of the key features of YouTube is the ability to view its videos on other web pages and client applications.

The YouTube APIs allows us to bring the YouTube experience to web pages, applications and devices.

YouTube .NET client APIs can be used by authenticated and anonymous users.

  • Anonymous user : Read only standard feeds.(Most Viewed,Top Rated,Watch On Mobile, Most Discussed,Top Favourites,Most Responded, Most Recent etc)
  • Authenticated user : Public feeds, private feeds (user’s inbox feed), upload, delete and update operations.

In order to user YouTube SDK, we have to perform the following initial steps

  1. Sign up for the Developer key. A Developer key uniquely identifies a product that is submitting the request. This Key should be provided in every YouTube API request
  2. Download and install .NET YouTube SDK

Default Location for the installed YouTube dlls

The following is a sample feed that we can parse manually to get video related information or this could be done easily by using YouTube .NET client APIs (there are three dlls in the package).

Example: Standard Feed –

In this article i am going to walk through a silverlight out of browser app, called silverTube.

This app got following abilities:

  • Fetching standard and private feeds,
  • Perform keyword search,
  • Playing videos, and
  • Hint of pagination capabilities.

Before stating the project, lets have a look at the end product.

Open the Visual Studio 2010 or Visual Web Developer 2010 Express with the Silverlight 4 tools installed.

Create a new silverlight project and name whatever you like. (here silverTube)

We already installed the YouTube SDK and now we need to have reference to them in our silverlight application. But silverlight runtime doesn’t allow to include those YouTube dlls in the project!

There is a workaround about this issue. We will add those dlls as well as a new WCF Service to our silverTube.Web project, and then our silverlight app can easily call that web service.

Add another reference to System.Runtime.Serialization.dll. The System.Runtime.Serialization namespace contains classes that can be used for serializing and deserializing objects.

Now add the following classes to the silverTube.Web project. Those classes will hold video meta data information.

We will now add a Silverlight-enabled WCF Service to this project and name it as svcSilverTubeServer.svc. Here i am using Silverlight-enabled WCF service template over the standard WCF Service because it is already pre configured and ready to use with Silverlight.

Insert the following namespaces


Before start coding lets have a look at the following diagram that will explain the base concept


Now we will write a private function called InitializeRequest that takes two parameters

  • prmUserName
  • prmPassword

If we provide valid Username and Password, then our intention is to get private feeds and also to perform upload, delete and update operation. Otherwise we could only get public feeds.


The following is the first public facing web service function for this project.

Our PrepareFeed method takes Atom feed collection and populate our custom collection for the later use


The GetYouTubeByKeyword method allows us to search videos by:

  • prmKeyword: a search query term
  • prmSafeSearch: Our intention to include all types of videos
  • prmOrderBy: Sorting our entries.
  • prmVideosBetweenTimeRange: A time period to limit standard feed results.
  • prmVideoCategory: Videos by categories.
  • prmCurrentPage: Current page no is the starting entry no.
  • prmPageSize: Maximum number of entries to return for the current page.

Have look at the method implementation. I guess its well commented.

Now its time to get private feed. Authentication is required for this purpose.


At this point we done with our WCF service. Now its time to consume the service in our Silverlight application.

Right-click the silverTube project in Solution Explorer > Select Add Service Reference > Click Discover to get following screen that lists all the supported operations and give a namespace as clientYouTube

Following XMAL is for our app that could be modified and extended by you. Based on the requirements your XMAL could be different than my one.


ImagePathConverter class:

Code behind for this app is very straight forward. So i am not going to explain here, you better please download the source.

Now we are going to configure the application so that it can be installed for out of browser use.

Right-click the silverTube project in Solution Explorer > Silverlight > Check Enable running applications out of the browser

There is one last thing we need to do is to add clientaccesspolicy.xml file in the silverTube.Web project. This configures the service to allow cross-domain access.

Throughout this article I tried to show you how searching and playing of YouTube videos could be done. In future i will look more into uploading and downloading YouTube videos.


Until than Happy coding.
Sumon Barua

 Download: Source


Silverlight 4 : Data Validation – Tip of the Day – Part 1

Data validation is very very important for all sort of data driven applications and websites. It is a purifying process where it ensures only valid data is being saved into the database. So, today I am going to talk about Data Validation in Silverlight.

By default silverlight doesn’t give any visual feedback when the data binding system encounters error relating to incorrect input. But what it does is, it rejects data internally.  At this point the user is under the impression that data has been saved. But its not the case. I agree with you, its misleading.

In this situation what can we do?

Yes, it would be nice if the silverlight data binding engine notify or alert us through visual feedback when there is a violation of rules. Lets start with simple application which will give us a simple basic ground for future advanced investigation on data validation.


Step 1 : Create a silverlight application and add the following Student class to your project

Step 2 : Open the MainPage.xaml.cs code behind and modify the MainPage() constructor that should look like the following section. LayoutRoot is our grid container.


Step 3 : There you go, XAML. The following section goes between UserControl tag.

Step 4 : Run the application and type any string in the age filed and then try to move your cursor to other control. As expected internal validation has happened by rejecting the invalid input with no visual feedback. But we want visual feedback, lets see what can be done to achieve this “Visual feedback” or “error message”.  

Step 5 : ValidatesOnExceptions is the very first step for implementing all types of validation.


ValidatesOnExceptions = True, by doing that, it will makes sure silverlight will provide visual feedback for the validation error. This property tells the binding engine that if any sort of exception happens during data transfer to the underlying data source, then treat the exception as a validation error.

Silverlight reports a validation error in the following situations

  • Type conversions failure.
  • When there is a error in binding object’s set accessor.
  • When there is an exception from validation attribute

Key points to remember:

  • Data binding must be TwoWay
  • ValidatesOnExceptions = True
  • When a TwoWay bound control (in our example, textbox) looses focus, the value gets updated to the source.

Now look at the modified XAML for the text boxes:

Step 6 : Run the application and type any string in the age filed and try to move your cursor to other control. This is like magic, now I can see the visual feedback from Silverlight app and this is about the wrong data type. But that’s not enough for me, I want to put a range validation(0 to 100) for the Age field. Don’t get bored, you might be wondering why Mr Sumon is proceeding slowly? Mate, that’s how I proceed. Lets move on …..


Step 7 : Now its time to modify the existing Student Class. Modify the Age property setter.


Step 8 : Run the application, at this stage the Age field is able to handle two types of validation (Invalid data type and Range validation). Now that we are clear on that, I am hungry for more adventure, just keep following me.

What I want now is that when there is an invalid input in the Age field, I want the textbox to have yellow background and also showing the error message via tooltip. I am just showing different ways but its up to you guys to drive your imagination.

Step 9 :

NotifyonValidationError = True

NotifyonValidationError = True, this makes the binding engine to raise the BindingValidationError event during the exception. This is a routed event which could be handled by the target control or by the parent container(more realistic). Again modify the XAML for the textboxes

So, I attached BindingValidationError event to the Grid container. The handler at the parent or container level could conceivably perform validation on multiple child elements.


Step 10 : Up to this point, we are having relative visual error feedback but we want more control! In BindingValidationError handler we can specify more validation actions. In our case wanted actions are, making the background yellow and showing error message using the tooltip for the guilty control.

Step 11 : I can’t wait to run the app. There you go!


I am happy that individual control is showing the related error messages and doing extra activities. I got another idea, it would to nice if I could show all the error messages in one place in a summary format. Does this ring a bell? Yes, we can achieve this through ValidationSummary control in Silverlight.

Step 12 :


Namespace:  System.Windows.Controls
Assembly:  System.Windows.Controls.Data.Input (in System.Windows.Controls.Data.Input.dll)

Using ValidationSummary control we can display a consolidated list of validation errors. By default, the control displays error for its parent container control. To specify a different container we have to set the Target property. Target property is null by default.

Quick steps:

  • Add a reference to System.Windows.Controls.Data.Input
  • Declare the namespace in the XAML markup.
  • Finally insert the ValidationSummary control tag.

Step 13 : Running the app should give you the following one.


Validation for the textbox happens when it loses focus, if the data is valid it gets reflected on data source otherwise gets rejected which is a default behaviour. But I want data propagation and validation to happen only when I click the save button, not when textbox looses focus . That means I have to change the default behaviour. This could be done using UpdateSourceTrigger property of the Binding object.

Step 14 :


UpdateSourceTrigger accepts two values:

  • Default
  • Explicit

UpdateSourceTrigger = Default indicates automatic update what it was doing until now. UpdateSourceTrigger = Explicit, to disable automatic updates to the binding source. That means, from now on you have to manually update the source. This is useful when user want to perform some sort of activities before the data propagation to source and on demand validation (i.e. in our case Button click event), not when textbox looses focus.



Step 15 : Now we will see how we could manually update the source which in turns fires the validation process. When user types invalid data and moves to other control, there should be no validation. Now validation only happens in button click.  

This is a multipart article and I want to take a break.  My next articles will be based on following topics:

  • Data Annotation
  • Validation with IDataErrorInfo and INotifyDataErrorInfo (This is new to Silverlight 4)

Can’t wait to start the second part of this article.

Happy Coding.
Sumon Barua

Download: Source