I have been looking around to build an open source Index.dat file viewer using .Net. It's not that there are no viewers available but I could not find any that were built using C# or .Net framework. So finally I ran into some old C code developed by FoundStone.com to develop a command line took named PASCO. So I took that code built a viewer of my own.

You can go to the following link to download source code for Index.dat viewer developed using C#.

Download Source Code (9.09 kb)

Download Binaries (6.28 kb)

Recently I started created some YouTube videos and wanted to embed them in my ASP.Net web site. YouTube provides Embed button next to each video and that helps you create HTML code that you can put on your page. But that would mean that you will have to hard code this HTML on all pages where you want to embed videos. Also if you want to show some random videos on the pages, then this approach is not flexible.

I created this ASP.Net server control that allows to embed YouTube videos on any page. The control allows you to embed videos for which you already have URL or you can configure it to fetch any of the standard YouTube feeds and then display random video from that feed.

How to use it?

• Download source code of the control and compile it or download pre-compiled binaries of the control.
• Add reference to ByteBlocks.YouTubeWeb assembly in your project.

• On the page where you want to embed YouTube video, add the following directive at the top of the page.

  <%@ Register TagPrefix="ByteBlocks" Assembly="ByteBlocks.YouTubeWeb" Namespace="ByteBlocks.Web.Control" %>

• Now add the control on the page.

  <ByteBlocks:YouTube id="youTubeVideo" runat="server" Width="480" Height="385" VideoUrl="" FeedType="MostRecent" RandomResults="true" />

• And you are all set to show random video from Most Recent video feed from YouTube.

Configurable Properties

• VideoUrl: This property allows you to set URL of the video that needs to be embeded.
• Width: Sets the width of the video player
• Height: Set the height of the videeo player
• FeedType: If you do not want to use a pre-defined video URL, you can pick a standard feed type. The control will fetch that feed from YouTube and display it based on value set for RandomResults and IndexToShow. This property is mututally exlcusive with VideoUrl. If you want the control to fetch standard feed, then do not set any URL in VideoUrl.
• RandomResults: This property indicates to control to pick a random Video Url from the list of videos from standard feed type.
• IndexToShow: If you set RandomResults to false, then the control will fetch the video at this index value. If this index is out of range, then the control picks the last entry in the feed list.

Under the covers

When you generate HTML code for a video from YouTube, it looks something like as shown below.

<object width="480" height="385">
<param name="movie" value="http://www.youtube.com/v/XcugLsKDmRs&hl=en_US&fs=1&rel=0"></param>
<param name="allowFullScreen" value="true"></param>
<param name="allowscriptaccess" value="always"></param>
<embed src="http://www.youtube.com/v/XcugLsKDmRs&hl=en_US&fs=1&rel=0" 
  type="application/x-shockwave-flash" allowscriptaccess="always" 
  allowfullscreen="true" width="480" height="385"></embed>
</object>

So the control simply renders this HTML on ASP.Net page and uses the control properties to configure the display accordingly. The important components of this HTML is video ID used with the video player. I have shown that in bold in snipper above. A video URL looks like as shown below.

http://www.youtube.com/watch?v=Qp9_6ACSWug

Video ID is provided in v query string parameter. The control parses this ID and replaces it in the URL that is required for URL for video player.

Source Code and Binaries

Attached code is compiled using Visual Studio 2010 and .Net 4.0 framework. If you need code for earlier versions of Visual Studio, feel free to conttact me.

This morning I was upgrading my HtmlParser and YahooFinanceParser libraries to use .Net 4.0 frameowrk. isual Studio 2010 conversion wizard did all the job of conversion. When I launched my test application to make sure everything was working, I was hit by a surprise. No code was changed other than compilation target was changed to .Net 4.0 and I got the following exception.

MethodAccessException

Attempt by method 'Winista.YahooFinanceParser.StockQuoteFetcher.GetStockQuote(System.String
to access method 'Winista.YahooFinanceParser.StockQuoteFetcher.CreateRequestAttributes(System.String)'
failed.

Since all assemblies were recompiled so the error details were not of much help asking to recompile with new referenced assmblies. I started with my usual ways of isolating the problem. Here was the call flow.

Console Application -->Library1 -->Library2

Exception was being thrown from a method in Library1. The exception message was not much of a help because it is complaining that class is having problem calling into its own private method. So I started my usual way of isolating the problem. The problem definitely seems to be code that was in CreateRequestAttributes. So I took the code out of there and directly put in the method GetStockQuote that was calling into CreateRequestAttributes. Now when i ran the test, i got the following exception.

MethodAccessException

Attempt by security transparent method 'Winista.YahooFinanceParser.StockQuoteFetcher.TestIt(System.String)' 
to access security critical method 'Winista.Text.HtmlParser.Http.RequestAttributes..ctor()' failed.

Assembly 'Winista.YahooFinanceParser, Version=4.0.0.0, Culture=neutral, PublicKeyToken=null' 
is marked with the AllowPartiallyTrustedCallersAttribute, and uses the level 2 security 
transparency model.  Level 2 transparency causes all methods in AllowPartiallyTrustedCallers 
assemblies to become security transparent by default, which may be the cause of this exception.

Now this exception detail made more sense. So let me explain what this issue is. In .Net4.0 framework, security tranparency rules prevent any security transparent code to call into security critical code. In .Net4.0 default security transpareny of library assemblies is security critical. My assembly Winista.YahooFinanceParser is marked with AllowPartiallyTrustedCallers attributes. This explicitly tells the security framework that this library will accept calls from security transparent callers. But the assembly Winista.HtmlParserPro do not have AllowPartiallyTrustedCallers attribute on it. This means it will not allow partial trusted or untrusted code to call into it. Therefore when method from Winista.YahooFinanceParser tried to create an object from Winista.HtmlParser, it threw MethodAccessException.

My original intention was to allow partially trusted to call into all these assemblies. But somehow AllowPartiallyTrustedCallers attribute slipped through the cracks for one assembly. After I applied AllowPartiallyTrustedCallers on Winista.HtmlParserPro assemnly, everything worked fine.

So if you are upgrading your libraries to .Net4.0 and you are not restricting any partially trusted or security transparent code to call into it, then put AllowPartiallyTrustedCallers attribute on your assemblies.

When we are creating a web site, one of the main goal we all have is that out site should be listed on first page of search engines like Google, Bing, Yahoo, Baidu etc. As we all know that in SEO world, one of the first thing we all look for in the page is meta tags in header of the page. In the past there was no direct way to set the meta tags on a page programatically when developing ASP.Net web site. We all used the work around of adding metaelements in header element of the page. You can read my previous post Adding meta tags to asp.net page dynamically about that technique. With ASP.Net 4.0 microsoft has introduced following two properties on that allow you to set the meta tags on a page.

• MetaDescription
• MetaKeywords

Following code snippet shows how it is used in your code.

public partial class _Default : System.Web.UI.Page
{
 protected void Page_Load(object sender, EventArgs e)
 {
  SetMetaTags();
 }
 private void SetMetaTags()
 {
  Title = "Hello Meta";
  MetaDescription = "This is description of my ASP.Net 4.0 page.";
  MetaKeywords = "ASP.Net,.Net4.0,Meta";
 }
}

And it works. You can see from the source of the page as shown below.

<head>
<title>Hello Meta</title>
<meta name="description" content="This is description of my ASP.Net 4.0 page." />
<meta name="keywords" content="ASP.Net,.Net4.0,Meta" />
</head>

Download Sample Project

This was a question was asked by one of my site visitors, Mike. Following is the text of the question:

This is a similar question to one you have already answered in formatting Grid Views. However there are 2 main differences. First: I want to change the value of a column (not the format) in any row if the row preceding it has a certain value in the same column.

This question translates to How do you change value of a data grid column based on values of previous row(s). I generalized this question to cover all previous rows and not just the proceeding row. Answer to all such questions relies on handling events like RowDataBound or RowCreated events. When a data grid or grid view renders, RowDataBound fires when row is being data bound and then RowCreated is fired after it has been data bound and row has been created. So depending on at what stage of rendering you want to change behavior of a row, you will subscribe either of these events. In the sample project, I am subscribing to RowDataBound event.

Next step is to access values from previous rows. Here you have choice. One, you can keep some local vaiable that stores values from previous row(s) and then use them in current row event handling. Two, you can access the previous GridRow based on index. In this sample i will discuss the approach of accessing previous row based on index and then extracting values from certain cells.

In RowDataBound event handler, GridViewRowEventArgs provides you access to DataItem associated with current row only. You do not have access to DataItem associated with previous rows. But at this point, previous rows have been prepared for rendering. You have access to all the cell values associated with previous row. You can access GridRow object of previous rows and extract text from cells that you are interested in. In the sample project, I am accessing ListPrice from fourth column and then displaying it in current row along with price associated with current row. Well, this does not sound like something that is very interesting or useful. But it serves the purpose of demonstrating you will accomplish the task.

Here is the code snippet from sample project.

protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
 if (e.Row.RowType == DataControlRowType.DataRow)
 {
  double price = -1.0;
  double prevPrice = -1.0 ;
  // Access the previous row.
  if (e.Row.RowIndex != 0)
  {
   GridViewRow prevRow = this.productsGrid.Rows[e.Row.RowIndex - 1];
   if (null != prevRow && 
    prevRow.RowType == DataControlRowType.DataRow)
   {
    double.TryParse(prevRow.Cells[3].Text, out prevPrice);
   }
  }
  var thisRowData = e.Row.DataItem as DataRowView;
  if (!Convert.IsDBNull(thisRowData["ListPrice"]))
  {
   double.TryParse(thisRowData["ListPrice"].ToString(), out price);
  }
  var ctrl = e.Row.FindControl("prevPriceLabel") as Label;
  if (null != ctrl)
  {
   ctrl.Text = string.Format("{0} - {1}", prevPrice, price);
  }
 }
}

Feel free to send me any request for any other grid view implementation you would like to be answered or implemented.