CompletIT Community Server

IsNumeric and Cast headache

idragoev — Fri, 13 Feb 2009 15:04:00 GMT

An interesting issue was found by a colleague of mine: an exception when cast a nvarchar column to integer even if the column value was checked with IsNumeric on SQL 2000 SP4:

select c.IDfrom dbo.COM_COMPANY c where IsNumeric(c.CODE) = 1 and convert(c.CODE as int) = 304 and DELETED = 0

As result the following exception were raised:

Msg 245, Level 16, State 1, Line 1Syntax error converting the nvarchar value '9665a' to a column of data type int.

I played a bit with this query and I found the following: if I delete the check for the DELETED flag it works fine. But when I add one more check then it throws an exception. Here the working version:

select c.IDfrom dbo.COM_COMPANY c where IsNumeric(c.CODE) = 1 and convert(c.CODE as int) = 304

But I really need to have more checks, so what can I do?

The answer is:

select c.IDfrom dbo.COM_COMPANY c where DELETED = 0 and     (case when IsNumeric(c.CODE) = 1 then cast(c.CODE as int) else -1 end) = 304

This one works just fine.

Enjoy the workaround ;-)

Missing exceptions in code after Raiserror() and SET NOCOUNT ON workaround

idragoev — Fri, 19 Dec 2008 10:59:52 GMT

These days I worked on a problem related with using raiserror() in SQL 2000 and why the exception is not raised in ADO.NET application using ODBCCommand. What I had is a simple stored procedure, that performs some check on its parameters and if some of them are incorrect it raises error and exits:

create procedure dbo.TestRaiserrrorinCode (@ClientCode nvarchar(10)) as

if not exists (

select Id

from dbo.Clients

where Code = @ClientCode)

begin

raiserror(58005, 16, 1, @ClientCode)

return 58005

end

print 'Do Something'

If you execute it in SSMS you will see:

Msg 58005, Level 16, State 1, Procedure TestRaiserrrorinCode, Line 8

Cannot find client with code '34'.

As you can see, because of the return the print does nothing. So in the SQL it works fine.

But what if you execute this procedure from the C# code using ExecuteNonQuery()? The exception is not raised and the procedure seems to be executed normally. But it is not – there is no exception in the C# code, but the procedure didn’t execute successfully either.

I started my investigation by playing sit SET XACT_ABORT ON, but it didn’t help – it was not related to this situation.

I tried to remove the return after the raiserror() call, but as you might know raiserror() do not stop the execution so I get ‘Do something’ printed, which is not acceptable.

What’s the solution?

I’ve noticed that I have missed the SET NOCOUNT ON and decided to add it. And miraculously it helped. The procedure worked fine, the C# code throws the exception.

How and why the SET NOCOUNT to ON affects this – I do not know. But the fact is that without it the procedure does not behave as it is expected.

Hope that helps you!

Animating ListBox items - the VisualStateManager

idragoev — Fri, 13 Jun 2008 13:13:00 GMT

Check out my second article on ListBox items animations. Here you can see how to use VisualStateManager and also some problems I faced during the migration to Silverlight 2 beta 2

Enjoy!

Moving ViewState to the bottom of the page

nraychev — Mon, 02 Jun 2008 13:51:00 GMT

We noticed that the ViewState in silverlightshow.net was enormous so we decided to make some improvements. The first step was to move it to the bottom of the page just for the search engine optimization. I have met many articles in internet which describe how to do this. One of them which I have used is:

http://www.hanselman.com/blog/MovingViewStateToTheBottomOfThePage.aspx

I’ll describe the solution which worked for us:

I created a class named SLSPage which extends the System.Web.UI.Page class and made all ASP.NET pages inherit this class instead of the Page class. Here our class is:

using System.Text.RegularExpressions;
using System.IO;
using System.Web.UI;
using System;
using System.Configuration;

namespace SilverlightShow
{
    public class SLSPage : System.Web.UI.Page
    {
        #region Constants
        private static readonly Regex viewStateRegex = new Regex( @"<input\s+type=""hidden""\s+name=""__VIEWSTATE""\s+id=""__VIEWSTATE""\s+value=""[^""]+""\s*/>", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Compiled );
        private static readonly Regex endFormRegex = new Regex( @"</form>", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Compiled );
        #endregion

        #region Handlers
        protected override void Render( System.Web.UI.HtmlTextWriter writer )
        {
            string originalHtml = string.Empty;
            string newHtml = string.Empty;

            using ( StringWriter stringWriter = new StringWriter() )
            {
                using ( HtmlTextWriter htmlWriter = new HtmlTextWriter( stringWriter ) )
                {
                    base.Render( htmlWriter );
                    originalHtml = stringWriter.ToString();
                }
            }

bool success = false;

Match viewStateMatch = viewStateRegex.Match( originalHtml );

            if ( viewStateMatch.Success )
            {
                string viewStateString = viewStateMatch.Value;
                newHtml = originalHtml.Remove( viewStateMatch.Index, viewStateMatch.Length );

Match endFormMatch = endFormRegex.Match( newHtml, viewStateMatch.Index );

                if ( endFormMatch.Success )
                {
                    newHtml = newHtml.Insert( endFormMatch.Index, viewStateString );
                    success = true;
                }
            }

            if ( success )
            {
                writer.Write( newHtml );
            }
            else
            {
                writer.Write( originalHtml );
            }
        }
        #endregion
    }
}

We have two constant, precompiled Regex objects. The first matches the hidden field named __VIEWSTATE and the second – the closing tag of the form. Note that our solution will work only if we have only one form – the server form, but it is common scenario in ASP.NET.

#region Constants
private static readonly Regex viewStateRegex = new Regex( @"<input\s+type=""hidden""\s+name=""__VIEWSTATE""\s+id=""__VIEWSTATE""\s+value=""[^""]+""\s*/>", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Compiled );
private static readonly Regex endFormRegex = new Regex( @"</form>", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Compiled );
#endregion

Then I override the Render method where we have full control on the rendered html.

In this method I declare two string variables – one for the original rendered html and one for the html in which the ViewState will be at the bottom.

string originalHtml = string.Empty;
string newHtml = string.Empty;

I use the Render method of the Page class in order to render the html into a HtmlTextWriter , named htmlWriter, which wraps a StringWriter named stringWriter. Then I use the ToString method of the StringWriter in order to load the rendered html in the originalHtml variable.

using ( StringWriter stringWriter = new StringWriter() )
{
     using ( HtmlTextWriter htmlWriter = new HtmlTextWriter( stringWriter ) )
     {
           base.Render( htmlWriter );
           originalHtml = stringWriter.ToString();
     }
}

Then I declare a Boolean variable called success, which by default is false:

bool success = false;

This variable will be set to true only if all operations for moving the ViewState succeed. The following code moves the ViewState:

Match viewStateMatch = viewStateRegex.Match( originalHtml );
if ( viewStateMatch.Success )
{
string viewStateString = viewStateMatch.Value;
newHtml = originalHtml.Remove( viewStateMatch.Index, viewStateMatch.Length );

    Match endFormMatch = endFormRegex.Match( newHtml, viewStateMatch.Index );
    if ( endFormMatch.Success )
    {
         newHtml = newHtml.Insert( endFormMatch.Index, viewStateString );
         success = true;
    }
}

If the first match succeeds I remove the ViewState, save it in a temp variable named viewStateString, save the changed html in the newHtml variable and continue with the second match. If the second match succeeds I insert the viewstate tag just before the closing form tag and set the success variable to true. So only if all operations succeed we can use the modified html, otherwise we will use the original. I make a check:

if ( success )
{
writer.Write( newHtml );
}
else
{
writer.Write( originalHtml );
}

I use the HtmlTextWriter named writer, which we accept as a parameter of the Render method. This method writes the html to the output.

There are several occasions when some of the matches will not succeed and the original html must be rendered. For example when we use Ajax controls where we have partial rendering. In this situation only a part of the page html is rendered and there is no ViewState.

The second step was to optimize the ViewState so now its size is reduced up to 95%. In fact we do not need any more to move it to the bottom because only a small part of it remained. So this solution was just temporary. But if you don’t have enough time to make optimizations you can use this solution.

Using the HyperlinkButton control in Silverlight 2 Beta 1

nraychev — Fri, 30 May 2008 14:13:00 GMT

I published an article about the HyperlinkButton, which you can see here:

HyperlinkButton in Silverlight 2 beta 1

Articles about Button controls in general and the Button control in Silverlight 2 Beta 1

nraychev — Mon, 12 May 2008 08:15:00 GMT

I published two new articles about Silverlight controls today:

The first covers the key features of the ButtonBase class, inherited in all button controls, you can see it here: Button Controls

The second one is dedicated to the Button control. Visit it here: Button Control

Using the Border control in Silverlight 2 Beta 1

nraychev — Thu, 08 May 2008 12:04:00 GMT

I completely forgot to mention my article about the Border control in Silverlight which I published a few weeks ago.

Here it is:

Using the Border control in Silverlight 2 Beta 1

SiteMap and URL Rewriting in ASP.NET 2.0

nraychev — Wed, 23 Apr 2008 09:04:00 GMT

Introduction

A common scenario in web development is when one page shows different content depending on some query parameters. OK, but these query parameters do not look friendly to the user and are neither friendly for the search engines. Here the URL Rewriting comes. We have URL rewriting in SilverlightShow.net sitemap page. Look for example here:

http://www.silverlightshow.net/Sitemap-Articles.aspx

You see that the articles are organized in pages and when clicking on “Older Articles” or “Newer Articles” the page is changed and the URL looks slightly different. Only the number at the end of the page name is different, for example “Sitemap-Articles-1.aspx” or “Sitemap-Articles-2.aspx”.

The problem

It’s needless to say that all these different URLs are processed by a single ASP.NET page. The problem came when we decided to put an ASP.NET SiteMapPath control. By default it automatically binds using the information provided in the Web.sitemap file. OK, we have the following SiteMap structure:

<?xmlversion="1.0"encoding="utf-8" ?>

<siteMapxmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >

<siteMapNodeurl="~/Default.aspx"title="Home" description="Home">

<siteMapNodeurl="~/Sitemap.aspx"title="Sitemap"description="Sitemap">

<siteMapNodeurl="~/Sitemap-News.aspx"title="News"description="News"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Articles.aspx"title="Articles" description="Articles">

<siteMapNodeurl="~/Sitemap-Announcements.aspx"title="Announcements"description="Announcements"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Products.aspx"title="Products"description="Products">

<siteMapNodeurl="~/Sitemap-Controls.aspx"title="Controls"description="Controls"></siteMapNode>

<siteMapNodeurl="~/Sitemap-MediaPlayers.aspx"title="Media Players"description="Media Players"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Games.aspx"title="Games"description="Games"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Charts.aspx"title="Charts"description="Charts"></siteMapNode>

</siteMapNode>

<siteMapNodeurl="~/Sitemap-Tools.aspx"title="Tools"description="Tools"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Moonlight.aspx"title="Moonlight"description="Moonlight"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Demos.aspx"title="Demos"description="Demos"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Learn.aspx"title="Learn"description="Learn">

<siteMapNodeurl="~/Sitemap-Videos.aspx"title="Videos"description="Videos"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Presentations.aspx"title="Presentations"description="Presentations"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Tutorials.aspx"title="Tutorials"description="Tutorials"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Resources.aspx"title="Resources"description="Resources"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Samples.aspx"title="Samples"description="Samples"></siteMapNode>

<siteMapNodeurl="~/Sitemap-QuickStarts.aspx"title="QuickStarts"description="QuickStarts"></siteMapNode>

<siteMapNodeurl="~/Sitemap-TipsandTricks.aspx"title="Tips and Tricks"description="Tips and Tricks"></siteMapNode>

</siteMapNode>

<siteMapNodeurl="~/Sitemap-Issues.aspx"title="Issues"description="Issues"></siteMapNode>

<siteMapNodeurl="~/Sitemap-Misc.aspx"title="Misc"description="Misc"></siteMapNode>

</siteMapNode>

<siteMapNodeurl="~/Sitemap-Shows.aspx"title="Shows"description="Shows"></siteMapNode>

</siteMapNode>

</siteMap>

We have the root website node, marked with title “Home” and the sitemap node marked with title “Sitemap”. All child nodes of the “Sitemap” node except the last child (Shows) are processed by a single ASP.NET page. Since the URL is different no matter that all these nodes are in fact one ASP.NET page the SiteMapPath works the way it has to work. For example if we are on the following URL:

http://www.silverlightshow.net/Sitemap-Articles.aspx

Our SiteMapPath is rendered the following way:

If you look at our Web.sitemap file you will see that it works fine. Till now everything is OK, but imagine that we want to open the last page in the Articles page, which is on the following URL:

http://www.silverlightshow.net/Sitemap-Articles-1.aspx

It works on SilverlightShow.net because we have made it work but in common scenario it wouldn’t work. No SiteMapPath would be shown because in the Web.sitemap we don’t have a node with url="~/Sitemap-Articles-1.aspx". You can always say that we can add this node too but in our case lots of articles are added to the site every day and the pages become more and more. I don’t like the option of checking for new pages every day and updating the Web.sitemap file.

The solution

The solution is to attach to the SiteMap.SiteMapResolve in the OnLoad handler of the page that processes the request where paging is needed.

We have the following code in the code behind of our page:

protected override void OnLoad( EventArgs e )

{

base.OnLoad( e );

SiteMap.SiteMapResolve += new SiteMapResolveEventHandler( this.ConstructSiteMap );

Note: You can do the same in the Page_Load method if your ASP.NET page is marked with: AutoEventWireup="true". I’m overriding the OnLoad event handler because it is faster :)

Note: SiteMap class is located in the System.Web namespace and is an in-memory representation of the navigation structure of the website. It is used by the SiteMapPath control.

Here is the handler for the SiteMapResolve event.

private SiteMapNode ConstructSiteMap( Object sender, SiteMapResolveEventArgs e )

{

SiteMapNode currentNode;

if ( SiteMap.CurrentNode == null )

{

currentNode = e.Provider.FindSiteMapNode( "~/Sitemap-Articles.aspx " );

}

else

{

currentNode = SiteMap.CurrentNode.Clone( true );

}

return currentNode;

}

In our case if the URL is with paging it is not found in the Web.sitemap file and that’s why the SiteMap.CurrentNode property will be null. This causes the SiteMapPath control to disappear. OK, now we check if this property of the SiteMap is null and if it is we just create a SiteMapNode using the current provider’s SiteMapProvider.FindSiteMapNode method giving the URL without paging. Note that we surely will know the URL that must be given to the FindSiteMapNode method because we are in the page which processes the request. If this property is not null we just clone it. The return value of our handler will be the SiteMapNode which will be used to render the SiteMapPath control.

This is a better solution than updating the Web.sitemap file every day.

Additional Issues and solutions

I found out that the SiteMap class has a strange way of caching. For example if we go to: http://www.silverlightshow.net/Sitemap-Controls.aspx our SiteMapPath will look like this:

After that we are going to http://www.silverlightshow.net/Sitemap-Articles.aspx and our SiteMapPath is normal:

But the problem comes when we go through the pages. If we hadn’t find a solution our SiteMapPath path would look this way, no matter that we are on the Articles page and not on the Controls page:

This behavior is as strange as our solution. It seems that the SiteMap remembered that when last time the CurrentNode was null we made it “~/Sitemap-Controls.aspx” and when we are on Articles page and this node is again null it uses the previous value from Controls. As I told you our solution is also strange but works :) We are putting our page path in variable instead of literal:

currentNode = e.Provider.FindSiteMapNode( this.currentPagePath );

Our variable of type string currentPagePath contains for example the following value “~/Sitemap-Games.aspx” for the following page: http://www.silverlightshow.net/Sitemap-Games.aspx. The behavior is exactly the same. But if we make this variable null just after our page is unloaded no caching takes place:

protected override void OnUnload( EventArgs e )

{

base.OnUnload( e );

this.currentPagePath = null;

}

Note: In our case our Controls and Articles pages are processed by a single ASP.NET page. But the caching behavior of the SiteMap takes place even these two URLs are processed by different ASP.NET pages. Our solution works for our Shows page which is different ASP.NET page. You just must make the variable which contains the current node path null on both places.

Using the GridSplitter control in Silverlight 2 Beta 1

nraychev — Tue, 15 Apr 2008 14:30:00 GMT

I wrote a little article about using the GridSplitter control.

You can see it here:

GridSplitter Article

I also wrote another article in response of a guy who asked me about how the Canvas control deals with the Measure/Arrange process when it is laid out by a parent Panel.

Here it is:

Canvas and Measure/Arrange

A few articles about layout controls in Silverlight 2 Beta 1.

nraychev — Wed, 09 Apr 2008 08:21:00 GMT

Hi to all :)

As a first post in this blog I'd like to present the articles about Silverlight which we published this week. They describe how to use the layout controls in Silverlight 2 Beta 1 and can be used as tutotials:

Yolu can see them here:

Layout controls in Silverlight 2 Beta 1

Using the Canvas control in Silverlight 2 Beta 1

Using the StackPanel control in Silverlight 2 Beta 1

Using the Grid control in Silverlight 2 Beta 1

DataGridView Extension 1.1.1 was released today.

iiordanov — Fri, 29 Feb 2008 16:13:00 GMT

DataGridView Extension 1.1.1 was published today and the full functional free version can be downloaded from here.
List of the fixed issues included in this new version are:

Added rows to unbound DataGridView control are not shown - described in this post;
Export of DataGridView using API results in black color of some of the exported cells;
Improved multithread operations when exporting;
Changes in API comments on classes, methods, properties, etc;
Other bug fixes.

What more has changed is that now the source code of the DataGridView Extension is available for sell from here.

CodeCamp Bulgaria

estoychev — Thu, 07 Feb 2008 11:40:16 GMT

The developer's community in Bulgaria organizes the first Code Camp on 15/16th of February 2008. I'm glad to see that such initiatives are held in my country as well. I'm sure it is going to be fun and this will be the first of many upcoming camps.

There will be 7 sessions:

Pingback and Trackback enable your web application
Multicore architectures and programming
CIFactory - continues integration on crack
Mootools
Aggregator How-To
Creating multiplatform .NET applications using Mono

I'm going to speak in the first one - Pingback and Trackback enable your web application. You can find more information on the official site - http://codecamp.sofiadev.org

Meet you there.

Interactive Silverlight Voting Control

idragoev — Wed, 05 Dec 2007 14:43:00 GMT

As you might know, we at CompletIT are behind the SilverlightShow.net - the independent Silverlight community site. Also, the last few weeks we've published several articles (with source code included) just to show how easy is to create nice stuff with Silverlight 1.1.

I also decided to write an article based on simple interactive voting control. The purpose of this control is to show the current results for certain vote. The site visitors can give their vote simply by clicking on the option result they like and the results are automatically updated.

We will continue publishing articles with source code. We hope such examples are helpful for the developers.

You can submit your own article Silverlight on SilverlightShow.net - just click here.

Silverlight 1.1 Tools Alpha - VS Orcas Beta 2 to VS2008 RTM migration issues

estoychev — Tue, 04 Dec 2007 09:10:27 GMT

Last week Silverlight 1.1 Tools Alpha for VS 2008 RTM were released and as a developer working with Silverlight I run to install them on my fresh new copy of VS 2008 RTM. The installation went without any problems, but unfortunately after trying to create a new Silverlight project (same for class library) I got a popup error saying:

"The project file 'C:\Users\estoychev\AppData\Local\Temp\zhxiyguv.4rr\Temp\SilverlightProject1.csproj' cannot be opened. The project type is not supported by this installation."

Puff. I tried to google about this error message but I got no helpful results. I only noticed that a guy commented on the ScottGu's blog with the same problem. Scott kindly replied to this guy to mail him and he would attach someone to help for this problem. I followed his advice and wrote to him. The next day I received an answer from Bill Hiebert guiding me how to resolve my problem. The simple step you should take is the following:

Open a Visual Studio Command prompt and type "devenv /resetskippkgs".

Then try to create a new Silverlight project. This solution does work for me. I hope it also works for you. Thanks Bill ;)

DataGridView Extension 1.1 Installation Update

iiordanov — Fri, 30 Nov 2007 10:08:00 GMT

DataGridView Extension's installation and archive for download were updated.
List of the fixed issues included in the new update:

Improved error handling in the Xml persistence;
Fixed a bug in themes import functionality;
Update of ‘Developers' guide’ and ‘End User Manual’;
Fixed bug in Pdf export font mapping – the Extension could not embed in the generated pdf document font which is a part of Font Type Collection file. Instead of that a default font is used;
Other small fixes and improvements.

DataGridView Extension 1.1 hit the streets with improvements, print and export to Pdf.

iiordanov — Sat, 17 Nov 2007 18:58:00 GMT

The new version of DataGridView Extension 1.1 has been relesed on time. In the new version you will find printing functionality, export to Pdf, many improvements and bug-fixes. You can download it from here or see the change log.

DataGridView Extension 1.1 will be released on the 13th of November 2007.

iiordanov — Fri, 02 Nov 2007 15:01:00 GMT

We are proud to announce that DataGridView Extension 1.1 will be released on the 13th of November 2007. This new version will contain new functionalities (such as Export & Import of themes, Print, Export to Pdf, UI Security and others) as well as fixes of issues reported by our users (thank you guys!). Developers guide will be also available for download, describing how to use, integrate, change and control the extension and its features in your applications.

CompletIT at DevReach, Sofia, Bulgaria 1-2 October, 2007

idragoev — Mon, 08 Oct 2007 15:36:00 GMT

At the beginning of October I have visited DevReach - the premier conference for Microsoft technologies in South Eastern Europe. I was on several lectures about MS SQL:

What's New in SQL Server 2008 for Developers - by Vladi Tchalkov;
T–SQL Querying: Tips and Techniques (With SQL 2008 features too) by Stephen Forte;
Lino Does LINQ by Lino Tadros;
Being Smart About Database Design by Vladi Tchalkov,
100 Years of Transaction Solitude...Transactions and isolation levels by Ami Levin;
SQL Server Service Broker - Your Gateway to the World of Transactional Asynchronicity by Ami Levin;
Security and .NET by Hadi Hariri;
Silverlight, Flash on Steroids by Lino Tadros.

What I appreciated most is the fact, that I had the chance to discuss different topics with the speakers. Most of them are experienced, well known in the community, with knowledge about the cutting-edge MS technologies.

I’m looking forward to meeting the guys again.

DGV Extension's installation and archive for download were updated #2

iiordanov — Sat, 15 Sep 2007 08:13:00 GMT

Now you can download our latest installation\archive with improved export to Excel.
An issue was found and described by one of our users in the following topic.

Please note that if you already have DataGridView Extension downloaded you do not need to download it again but just the assembly 'DGVEExcelExporter.dll' and replace the old one you already have.

SilverlightShow.net - Silverlight Community

estoychev — Sat, 01 Sep 2007 15:12:00 GMT

Today we've published our first beta of SilverlightShow. It is a website that provides regular aggregation and classification of the information related to Silverlight available all over the Internet. We will get interviews, make video/audio/screen casts, write articles, provide samples; we will try to bring to you the hottest articles around Silverlight. As it is still a beta version there are no benefits to be a member of the community but soon we will provide functionalities to publish your own articles.

Currently we aggregate news from different sources - blogs, user groups, etc. We categorize the information carefully and let you see only the valuable pieces of it. Probably now you use RSS/Atom feeds or Google Alerts or Google Blog Search to stay in touch with the latest news around Silverlight. Yes, we also use these 'tools'. We also check the official Microsoft Silverlight Community site. We know about all of them. But we strongly believe that we can offer you more - a better experience to stay tuned with Silverlight.

I hope you will see in SilverlightShow a great place to learn and discuss things about Silverlight.

ASP.NET 2.0 issues: Validation of viewstate MAC failed

estoychev — Fri, 31 Aug 2007 11:44:00 GMT

Have you ever experienced such error? Well, today I did. It is not easy to get it - you have to browse too quickly trough pages (or in one page) and click buttons (causing postback). Yep, sounds strange. The point is that if you have a page, with lets say just a text box and a button, and you push that button quickly you will probably get this error - especially if you do it with slow connection or at least not on your local machine.

I would reccommend reading this thread in ASP.NET forums if you want to learn more about this error and want a solution (or a workaround).

DGV Extension's installation and archive for download were updated

iiordanov — Fri, 31 Aug 2007 11:32:00 GMT

Now you can download our latest installation\archive with improved file structure and sample project in C#.

DataGridView Extension 1.0. Release

idragoev — Fri, 17 Aug 2007 12:27:00 GMT

When Microsoft released .NET framework 2.0 the DataGrid control was replaced by DataGridView, which allows the developers to control better the way the data is presented by creation of much more user friendly views, but even in DataGridView control there is missing functionality.

And here is where the DataGridView Extension component comes, it is absolutely free and extends the functionality of the standard DataGridView control by adding themes support, searching data, export to Excel and HTML, etc.

Moreover, DataGridView Extension allow end-users to control the whole appearance at run time – columns size and order, formatting, colors, borders, etc.

The developers can easily integrate DataGridView Extension in their existing application in two simple steps:

Add reference to DataGridViewExtension.dll and the dll for exporting to Excel (DGVEExcelExporting.dll) and to HTML (DGVEHtmlExporting.dll) if needed.
Drag & drop DataGridView Extension Component on your root container from the toolbox then select the grid you wish to manage and set the value of its property ‘IsManagedByExtension’ to true

As a conclusion we can say that the DataGridView Extension brings direct, visible, benefits to the applications’ end-users by giving them control over the presentation of the data at run-time as well as export to external well known formats.

You can learn more about DataGridView Extension here.

Composite Design Pattern in C#

ppopadiyn — Thu, 02 Aug 2007 16:08:00 GMT

Introduction

The composite pattern is very simple pattern that has significant implication. The fundamental structure of the Composite pattern is shown on the next figure:

The base class Shape has two inheritors: Rectangle and Ellipse. The third inheritor is the composite. ComposeShapes holds a list of Shapes. An instance of ComposeShapes appears to be a single Shape. It can be passed to any function that takes a Shape, and it will behave like one.

2. Implementation

There are different implementations of the Composite pattern. I will show you one of them with the following example. Consider the following situation. Imagine we have a small company, which started with a single person (the boss). After some period of time he hired three people to help him with the business. Two of them became vice-presidents and the third became the finance manager (for example). Soon each of them hired new staff. As the success continues the company grows till the following sample structure is reached:

2.1 The IEmployee interface.

Each of the company members should receive a salary, have a boss and subordinates and should of course have some specific position. So in that case we will define a single interface named IEmployee that will declare all actions that each company member could implement.

public interface IEmployee
{
       string Name { get; set; } // get name
       decimal PricePerHour { get; set; }
       Position Position { get; set; } // get position
       IEmployee Boss { get; set; } // get boss
       List<IEmployee> Subordinates { get; }
       decimal GetSalary( decimal workHours ); // get salary
       void Add( IEmployee employee );
       void Remove( IEmployee employee );
}

Note that I have declared two additional methods (Add and Remove) in the IEmployee interface which functions are for adding and removing subordinates. These two functions are quite IMPORTANT, because they may cause overhead of the developer who design the Composite pattern. Why? I will discuss later. Now let’s come back to our implementation. I will define an enumerated type to create a structured set of constants that will represent some available positions in the company.

public enum Position
{
       None,
       Boss,
       VicePresident,
       Secretary,
       MainManager,
       SalesManager,
       Cleaner
}

2.2 BaseEmployee class.

Next we will implement our concrete BaseEmployee class that will store the name, salary (price per hour), position, parent (boss) and subordinates of the employee.

public class BaseEmployee : IEmployee
{
       private string name;
       private decimal pricePerHour;
       private Position position;
       private IEmployee boss;
       private List<IEmployee > subordinates = new List<IEmployee >();
       public BaseEmployee( string name, decimal pricePerHour, IEmployee boss, Position position )
       { // Intialize all private fields ............ }

       // Properties ......................
       public virtual void Add( IEmployee employee )
       {
              throw new InvalidOperationException( "Cannot add in base employee class" );
       }
       public virtual void Remove( IEmployee employee )
       {
              throw new InvalidOperationException( "Cannot remove from base employee clase" );
       }
       public virtual decimal GetSalary( decimal workHours )
       {
              return workHours * pricePerHour;
       }
}

It is obvious that the aim of the private field ‘subordinates’ is to keep a reference to each subordinate in the Collection of each Employee class. It also allows us to move downwards the chain from the president to each employee. But to keep our structure flexible enough we also need to move backwards to find out who an employee’s boss is. This is easy to implement, we just provide a constructor for each subclass that includes reference to the parent node - his/her boss. Of course for the boss of the company we will just pass ‘null’ to the constructor. The GetSalary method just gives us the salary of each employee. We also define some casual properties. Note that we do not implement the two problematic methods ‘Add’ and ‘Remove’, we only throw an exception in case these methods are called in the base employee class.

2.3 Employee class.

Our Employee class is a subclass of BaseEmployee and allow us to store subordinate employees as well. We will store them in generic List, named subordinates.

class Employee : BaseEmployee
{
       public Employee( string name, decimal pricePerHour, IEmployee boss, Position position )
              : base( name, pricePerHour, boss, position )
       {
       }
       public override void Add( IEmployee emp )
       {
              this.Subordinates.Add( emp );
       }
       public override void Remove( IEmployee emp )
       {
              this.Subordinates.Remove( emp );
       }
}

Here we finally implement the ‘Add’ and ‘Remove’ methods. If we make a summary, all these classes and methods could be represented in the following rough diagram:

Now we can start building our company structure. First we will create the president of the company, and then add his subordinates and their subordinates and etc.

3. Advantages, Disadvantages and Analyses.

The Composite pattern allows us define a class hierarchy of simple objects as well as some more complex composite objects, in each case they appear to be the same to the client. So the big advantages is that the nodes and leaves are handled in the same way. The Composite pattern also makes it easy to add new kinds of components to your collection, as long as they suppost similar interface. On the other hand this leads to a big disadvantage, your system will become too general. It will be hard to restrict certain classes where this normally is desirable. Sometime it is necessary a composition to have only specific components.

It is easy to add a new components to the structure, without changing the client code.

3.1. Explicit reference to the parent.

Holding references in the components to their parent is useful and can simplify the traversal of the tree (moving through all nodes (in this example – all employees) of the heirarchy), removing and adding new components. One available place where you could place this reference is in the ‘BaseEmployee’ class. And then all its subclasses can just inherit the reference and the methods that control it.

But in this case it is very important to keep synchronization between parents and children. That means, all successors should have a parent, and on the other hand this parent should have them for own children. The easiest way to do this is to change the parent of the given component when you add or remove components. If it is possible this feature should be implemented in the ‘Add’ and ‘Remove’ operations and then all this work will be done automaticly.

It is also possible to share a component. That mean one component may have more than one parent (in this case one employee may have more than one boss). But that case may lead to overhead.

3.2. The IEmployee interface.

One of the purpose of the Composite pattern is to hide the details of the class ‘Employee’. To do this the IEmployee interface should define as much as possible operations.

3.3. The ‘Add’ and ‘Remove’ operations.

Although in the interface ‘IEmployee’ we declare these two operation, there is a very important question: Which classes should implement these operations. Should we declare the operations ‘Add’ and ‘Remove’ in the ‘IEmployee’ interface (meaning that the ‘BaseEmployee’ class (the Component) must implement them)? Or, should we declare and define the operations only in the Composite class (Employee). The decision includes compromise between security and transparancy.

Consider the following situation: we have the same design as the example above, but suddenly we decided to derive the ‘BaseEmployee’ class and to create new components with specific characteristics. On the other hand only the composite class (‘Employee’) can add and remove components from the hierarchy. That mean that a non-leaf node can have a child-leaves added to it, but a leaf node cannot. So we want all components in the composite to have the same interface and to be treated equally. However that mean we will lose security because the clients may try to do foolish actions, like a adding and removing objects from the leaves.

If we declare and define the operations ‘Add’ and ‘Remove’ in the Composite class (Employee), we will win security, but on the other hand the Components and the Composition will have different interface.

3.4. Ordering Components.

In some programs, the order of the components may be important. If that order is somehow different from the order in which they were added, then the parent must do additional work to return them in correct order. For example, you might sort the collection alphabetically and return a new sorted collection.

3.5. Caching the result.

If you frequently ask for data that must be computed from a series of child components, it may be advantageous to cache these computed results in the parent. However, unless the computation is relatively intensive and you are quite certain that the underlying data has not changed, this may not be worth the effort.

4. Usage.

Use Composite pattern:

When you want to define a class hierarchy of simple objects or more complex composite objects.
When you want the clients to ignore the differences between the composite objects and the individual objects. The clients will treat equally all objects in a complex structure.

5. Conclusion.

The advantages are significant. Instead of duplicating the list management and iteration code in each of the clients, that code appears only once in composite class. So my advice is: use it ! ;)

4 reasons to switch to Visual Studio 2008 (formerly known as Visual Studio code name “Orcas”)

estoychev — Sun, 22 Jul 2007 00:37:00 GMT

Microsoft aims to release Visual Studio 2008 by the end of this year. Currently there is a beta 1 and a second beta release is expected later this summer. There is a couple of improvements in the new version of the most popular software development platform that could probably make you switch from an older version.

Multi-Targeting Support

Visual Studio 2008 will now support targeting multiple versions of the .NET Framework. That means you can open an existing project or create a new one and select the .NET Framework version to work with. No matter which version you choose you will be able to take advantage of the new features Visual Studio provides.

LINQ Support

Language INtegrated Query (LINQ) extends C# and VB with native language syntax for queries and provides class libraries to take advantage of these capabilities. It is a set of APIs that allows you to write SQL-like queries. LINQ is available only when .NET Framework 3.5 is used.

JavaScript intellisense and debugging

Built-in support for JavaScript intellisense and debugging (improved). One of the coolest things is that VS 2008 allows you to set client-side breakpoints directly within your source files.

Richer WYSIWYG Designer

VS 2008 will now support nested ASP.NET master pages at design-time. Master page support was one of the most popular features shipped with ASP.NET 2.0. But the drawback with VS 2005 was that nested master pages couldn't be edited with the WYSIWYG designer.

Split View support – source and design views available at the same time.

Rich CSS Support – CSS property window, CSS inheritance viewer, CSS preview, and CSS manager. This allows the designers/developers to easily create, manage and refactor CSS rules.