A book is born!!!

As most of you know, I was involved in writing a book about C# programming (we were 30 authors, each had to write a chapter and edit a chapter).You can click on its cover in order to be taken to download the PDF version:

Hope you will enjoy it.

Oh, almost forgot – it is in BULGARIAN . There were some plans to have it translated but as I am not a part of telerik anymore, I don’t have any information from the kitchen how far this project went.

Please be sure to say a great thanks to telerik for sponsoring this book!

Convert string to a known type (using its default converter)

I was in a need to get a type, instantiate it and then fill its properties (I'm currently doing an engine that will give me an instant CRUD UI).

So what I basically needed was to be able to fill a new object instance out of a Hashtable (the key is the name of the property and the value is its string representation).

I wanted to be able to convert that string value into the type it needs to be.
Here is some code to help you get it:

foreach(string strPropertyName in htValues.Keys)
{
PropertyInfo pi = entity.GetType()
.GetProperties()
.ToList()
.FirstOrDefault(property => property.Name == strPropertyName);
}
(this is kind of pretotype so don't blame me if you don't like the code :).

In the above code I am iterating in the keys of the hashtable, so if I have an user object it will strPropertyName will hold "FirstName", then "LastName".
So far so good, I am able to fill the object and send it to the EntityFramework for DB Persistance.

The problem was when the strPropertyName was holding "BirthDate" as it is a DateTime and the EntityFramework or the Reflection (not quite sure which one) was crying it can't Convert the string to the respective type for me.

Here is how I solved the problem:
// Create a new Instance of the given type.
object entity = Activator.CreateInstance(this.EntityType);
// Iterate through all the properties.
foreach(string strPropertyName in htValues.Keys)
{
// Get the property with that name:
PropertyInfo pi = entity.GetType()
.GetProperties()
.ToList()
.FirstOrDefault(property => property.Name == strPropertyName);
// Get the default type converter for the given property type:
TypeConverter converter = TypeDescriptor.GetConverter(pi.PropertyType);
// Set the value by converting non-values to the given type
// and setting null where it is a null value.
pi.SetValue(entity, htValues[pi.Name] == null ? null : converter.ConvertFromString(htValues[pi.Name].ToString()), new object[] { });
}

Basically the thing you (and I!) need to remember is that the TypeDescriptor class has a GetConverter() method that takes a type and returns a TypeConvertor for that type.

Now in order to be able to convert from string to that type you just need to call .ConvertFromString(string value) of the TypeConverter returned by the TypeDescriptor.

Hope this helps someone out there. To me it seems it can give you a great deal of abstraction and I (for some reason) believe this is heavilly used in nowadays OR/M's.

Get the underlying type out of a Nullable

It appeared to be really simple actually, this post title suggest the solution:

Type nonNullableType = null;
if (property.PropertyType.IsGenericType && property.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))
nonNullableType = new NullableConverter(property.PropertyType).UnderlyingType;
else
nonNullableType = property.PropertyType;

What we actually do is to check if the type is nullable or not, if so - we are getting its Underlying type, and if not - we are getting the type itself.

Check if a type is Nullable or not

I was in a need to determine if the type of PropertyInfo is a nullable or not.
Here is what I've found on MSDN about this:

property.PropertyType.IsGenericType && property.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>)

So you basically need to determine if the type is generic (makes sense as nullable is a type that takes T (Nullable)) and then to check if the type is a Nullable then.

Now, I really wondered do I really need both checks?
As it was coded that way at MSDN I first didn't look at that, but I wanted to tackle it a bit more.

First I thought that the first one is needed to protect you from the null value returned by the GetGenericTypeDefinition() method.
But what's the problem even if it does?
Well, you get InvalidOperationException saying "This operation is only valid on generic types.".

So you definetelly need both checks ;).
It is kind of ugly for me, maybe it will be better to create an extender to the Type type. Something like "IsGeneric()", but the Is prefix always suggests property while this is a method.

Anyway, I'll go with that.
In the next post I'll show you how to get the type out of a Nullable<>.

Programming - Rule #1 follow your data from the UI to the Database and back

It can save you a lot of time :).
I had to fix a bug with a value not updating on the UI.
I attached with the debugger and followed the code to the Save() method of the manager.
Then I started looking for some problems in the database (asynchronous triggers failing etc.).

I wasn't quite sure where the problem is for a while.
Then I decided to hit F11 on the Save() method of the manager with the hope to see what query it was generating.

Guess what?
It wasn't the query but the fact that the Manager was overriding the Base Manager Save() method, as it needs to convert a DTO object to DataObject in order to save it.
Well I didn't even need to read through all the properties to know for sure that the property that wasn't updating was missing in the list of assignments in the convert method (in order to defend myself I would say that 99.9% of our managers aren't overriding save methods, it is very unlikely so I didn't considered that to be the problem).

Happy coding and remember Assumptions are your worst enemy :). They are the things that waste most of your time.

Serializing object to JSON returns empty string?

Consider the following code:

string JSONObject = string.Empty;
DataContractJsonSerializer serializer = new DataContractJsonSerializer(this.GetType());
using (MemoryStream ms = new MemoryStream())
{
    serializer.WriteObject(ms, this);
    // Donchev - we need to reset because the write has gone to the end of the stream
    // and the StreamReader.ReadToEnd() won't seek to the beginning of the stream again.
    using (StreamReader sr = new StreamReader(ms))
    {
        JSONObject = sr.ReadToEnd();
        sr.Close();
        sr.Dispose();
    }
    ms.Close();
    ms.Dispose();
}
return JSONObject;

It seems perfectly correct but have a few problems.

And the first one is very important – it is based on wrong assumption and it is returning empty string because of that.

I will let you tackle it for a while to see if you can find where the problem is.

Ready?

If not – I’ll tell you – the problem is that when I wrote this code, I was expecting the ReadToEnd() method of the StreamReader class to auto reset the stream to its beginning, it sounds for some reason to me that this method it is saying - “Read the whole thing.”.

Unfortunately this assumption evaluated to false.

The method actually says - “Read from where you are to the end of the thing.”.

So before calling JSONObject = sr.ReadToEnd();

I needed to simply call:

ms.Seek(0, SeekOrigin.Begin);

In order to reset the pointer to the beginning of the stream.

Voilla!

The other question I asked myself is why the pointer is at the end of the stream (after the string is empty and not some portion of the stream, it should be at the end).

The answer – the serializer.WriteObject() method is probably not resetting it to be at the beginning after it completes its job.

Not quite sure who is responsible for resetting the stream – the caller or the callee, we can have a long discussion about this.

Anyway – just wanted to share this with you. I know it is very old thing but I am trying to write for much of the things that made an impression on me.

Very old stuff – convert System.Drawing.Color to HTML.

When I was with Delphi, I wrote utility to do this myself (I mean Delphi in its early days) as I wasn’t aware for built-in mechanism to achieve that.

Now with .NET there is utility to do this for you but I often forgot which class has static method to convert System.Drawing.Color to Html string.

Here it is:

System.Drawing.ColorTranslator.ToHtml(color)

I think wouldn’t it be smarter to have an extender attached to System.Drawing.Color to do this for me from now on … :).

Having column display name in RadGrid Column chooser but not in the header of the grid

A little bit of background for this one.

I had a Telerik RadGrid that was having few columns ...

It had the column chooser enabled. Few of the columns were icons (for example “Answered”, “Rating”).

I wanted to have them without header text so I added the Template column and everything was just fine.

Until I right clicked on the header in order to show the column chooser. It was displaying the columns with auto generated names like “GridTemplateColumn7”, “GridTemplateColumn10”.

My goal was to keep the header of the grid clean (e.g. no label) because the icons were 16x16 and that’s all the space I needed to occupy with those columns, having a header “Answered” would extend the entire column. So to solve this case here is what I did:

Solution:

1. Added header text to the column and saw that the header text is appearing in the column chooser.

2. To hide it from the header of the column I added an empty <HeaderTemplae>.

The column should look like this:

<telerik:GridTemplateColumn HeaderText="Bookmark">
    <HeaderTemplate>
    </HeaderTemplate>
    <ItemTemplate>
    </ItemTemplate>
</telerik:GridTemplateColumn>

 

This would solve the problem for Template columns (and all column types that allow you to define HeaderTemplate). This will not work for GridBoundColumn for example as this type doesn’t have HeaderTemplate.

 

Hope this helps someone out there …

Copy XmlNode from one XmlDocument to another

This one is more for the archive, but it is not widelly used so you may not know it.

In case you need to copy XmlNode from one XmlDocument to another, you need to do two things.

1. Import the XmlNode from the source XmlDocument to the target XmlDocument, using Import(XmlNode node, bool deep) method of the target node,
2. Get the result from this method (it is XmlNode) and use AppendChild method of the node that should be parent of the node to be transfered.

In other words:
XmlDocument sourceDocument = new XmlDocument();
XmlDocument targetDocument = new XmlDocument();

sourceDocument.LoadXml("");
targetDocument.LoadXml("");

XmlNode nodeToImport = sourceDocument.SelectSingleNode("//nodes/sourceNode");
XmlNode importedNode = targetDocument.ImportNode(nodeToImport, true);
XmlNode parentTargetNode = targetDocument.SelectSingleNode("/nodes/targetParentNode");
parentTargetNode.AppendChild(importedNode);

is enough to import the sourceNode with all its child nodes under the targetParentNode of the target document.

Site is recycled + ThreadPool.QueueUserWorkItem

Just to let you know that you may experience this issue.

If you have an unhandled exception it may be because of a job queued using ThreadPool.QueueUserWorkItem method.

Actually it appears that although the exception is not affecting the main thread (it was in another one) - the .NET will kill the running process (w3wp in our case).

As far as I read this behavior is implemented since .NET Framework 2.0.
It is because you may miss unhandled exceptions in a child thread (if it's in the main thread the process will be terminated in a windows application).

I imagine each request to a web server as a separate thread so I am kind of worried why unhandled exceptions aren't killing the W3WP process as well.
It only seems to be killed if you create another thread in the request thread and this another child thread exits with unhandled exception.

Will need to investigate a bit more about that.

How does your manager make a coffee?

I had an architectural problem yesterday.
I was working on a methods and managers I won't disclose but will analogy instead.



Imagine you have a coffee manager. Let's name it CoffeeManager.
In my case not only I had coffee manager but also I had a SugarManager, a CupManager etc.

In order to take a coffee without sugar in a plastic cup I should do something like:

Sugar sugarObject = SugarManager.GetSugar(Sugar.None);
Cup plasticCup = CupManager.GetCup(Cups.PlasticCup);
Coffee shortCoffee = CoffeeManager.GetCoffee(sugarObject, plasticCup);

And this happens at the very frontend of the project (in ascx for example).
And not only it happens that way but the managers are spread in few different projects.

So in the frontend I need to call few different managers, get some results from them and pass those results to the manager that should be doing my job.

I also need to handle all the problems that may rise in the managers so I get a lot of code in the frontend just to get something that in my opinion for that particular case should be returned calling a single method and auto handled in the manager.

I think the front end shouldn't care about business operations that much, also as I said the managers were in different assemblies so I ended up adding few references to the frontend project.

I refactored the code so the CoffeeManager can do this job internally (drawback is that the matrix of all combinations of sugar and cup should be added as a methods in the CofeeManager, but I can live with that).

String.Format

Although very convenient for example for making templates and then replace with some values, it may cause tricky problems.

I've reached a code where it was used to add some data to a javascript.
So javascript uses a lot fo curly braces, which are at the same time used for string format to know where to put its values.

There is a way to escape those braces, buy double them, so for example :
function {}
will become
function {{}}

Recently I had the "String was not in a correct format." exception. I tried to debug and found nothing wrong with the string and the values that will be placed.
That was because I was expecting the values to be wrong (null references, something like this) and not the string itself.

Guess what did I discovered after a few minutes of debugging?
It was the string that was corrupted. The problem was that this particullar javascript was in the .ascx file. Someone probably hit the CTRL + K + D so the source was re-formatted, addding some white spaces in between the doubled curly braces.

Be warned that string.Format is kind of fragile when it comes to files that may involve curly braces.

How do you unit test encryption?

I wrote two extenders to be used on the string type.
So you can say "test".Encrypt() and "encrpyptedtest".Decrypt().

I was wondering how to unit test this thing.
The first approach which was really obvious was to encrypt the string and then decrypt it, if you get the string before you do those two actions on it - the encryption is correct.

The question in this approach is : What do you test? do you test the encryption or the decryption?
You can get a false positive result this way. For example if the Encrypt method returns the same string without changing it and the Decrypt method returns the same string without changing it - the test will be passed (the string after encrypt -> decrypt will be the same as it was before).

The other approach is to hardcode encrypted and decrypted string, then pass the decrypted string to the Encrypt() method and see if the result matches the encrypted string.
Then pass the encrypted string to the Decrypt test method and see if it matches the decrypted string.
The question here is "What happens if someone change either the key or the initialization vector for the encryption?".
The test will fail as the strings no longer match (unless you are very very lucky to hit some collision case :), but the methods are valid and they work correctly.

For now - I will use the second method. I will hardcode an encrypted / decrypted pair as well as the key and the IV used for the encryption / decryption.
I will first check if the key and the vector match the one that were used to generate the pair and if they don't - the test will be inconclusive so the guy who changed either the key or the vector can easilly find the problem and resolve it.

Anyway I am really interested in how would you do such a task?

Two-way binding is only supported for properties exception.

That was very strange. I used #Bind in the markup of a user control in order to set a property value and got this nasty exception.

It told me nothing. I couldn't figure out what was wrong with the property and what does it mean that the property is not valid.

I did what every one of you will probably do ;)
Google with the exception and found that if you convert the property from the type it has to string it should work.

Couldn't make it.
Probably my scenario is different.
I will write another blogpost as soon as I find the solution. For now I worked it around another way - using the code behind ;)

Introduction to programming with C#

As Vesko Kolev stated in his blog - a new bulgarian book about C# programming is in progress.
I decided to take part because it seems very interesting. I haven't much experience in publishing so it will be very beneficial for me to work on this.
Actually I was author in a software magazine few years ago (as far as I remember I was about 17 years old so it must have been about 6 years ago). It should help me as I took the first chapter - introduction to programming where I will show the readers how to install Visual Studio 2010, how to start their first project and how to write their first program, some diagrams of the .NET framework 4.0 will also be included in this chapter.

We decided not to include any advanced features in this book, just core programming language, no extensions, no lambda expressions, no var, no automatic properties, no nothing.
This is because this book targets potential software developers and not software developers. It should show the developer how to code, how to think etc. We decided that if a man / lady without any software experience may think that auto property won't take memory after it doesn't involve variables (at least visualy :).
That is why we do only core things.

Wish us luck. We would really love to expand bulgarian software development community with few more people :). After all if even one guy / gal of all the people that will potentiall read the book becomes an expert - our mission would be completed (we are dreaming for more impact ofcourse :).

As Svetlin Nakov and Vesko Kolev said - telerik is sponsor for this book so it should be published easilly than their prеvious book - "Introduction to programming with Java" and would probably joy some more marketing efforts.

That was it about the book.
Now about my motivation to join the project no matter my personal engagements and all the work I have at telerik and at the university.
The first reason is that I am a self - taught (almost) developer.
I never had degree that will help me find my work, join some society of developers that will help me when I hit a difficult problem.
There wasn't even internet in my hometown. A friend of mine gave me a book on programming with Delphi (that Sams 21 days brick :).
The Delphi help also helped me and I also downloaded html files to read later when I was at school.

Then I applied for a job in the city where I was studying (Veliko Tyrnovo).
It was all my collegues that helped me improve my skills.
I don't feel as a worldwide recognised expert or something but getting to the intermediate level from nowhere is achievement to me.
So reason #1 to join this book is to give something back.

Another reason is that I would like to see how a book is written, are there different proccesses than in the software development. It has something to do with the blog posts I guess :)
So reason #2 is to steal some knowledge :)

And some kind of nostalgy would be the last reason to join :).As I said, I was an editor in a software magazine, it was very nice thing to do. The article, then the readers asking for some more information. I miss this a bit :)
Reason #3 - to feel the old days when I was an editor :)

Determine if your site is running under IIS or Casini

For the people who don't know - Casini is the built in Visual Studio server which is by default running when you debug ASP.NET project.
You can use the following to check if the site is running under IIS:

bool isUnderIIS = this.Request.ServerVariables["SERVER_SOFTWARE"].IndexOf("IIS") > -1;

Not the most clever thing I've ever done but seems to be the only way at the moment.
If you know a better way - let us know...

To clarify - IIS will return something like : "Microsoft-IIS/5.1", while Casini will let you bump your head with string.Empty.
Anyway, this covers my scenarios 100% so I can use it.

Work in a cooperation with your compiler. Always tell the truth about your datatypes!

When you have a cast you should avoid asking the compiler to figure out what kind of data should be returned. This is more about objects and the string data type.
For example I've seen (and to be honest I myself did the following mistake when getting data from DataSet. Don't laugh in .NET 1.1 and 2.0 there was no Linq :)

foreach (DataRow row in dsReportSource.Tables[0].Rows)
{
string strName = row["name"].ToString();
}

The compiler will let you think that it knows how to do the fastest transformation from object (in the dataset all the columns in a row are objects) to the destination type (in our case - string). But it will only let you think so. What will actually happen is that the compiler will slow down the data acquisition due to some internal checks and conversions ...

Instead do the following (as you are more than sure that this column is string):

foreach (DataRow row in dsReportSource.Tables[0].Rows)
{
string strName = (string)row["name"];
}

This way you tell the compiler - "Look, don't even bother to try to infer the type for me. I am telling you this is a string, so please just treat it as string). And it makes sense - after you have a column of type NVARCHAR in the database it will always come to you as a string (masked as object :).

Now there are even worse cases like:

foreach (DataRow row in dsReportSource.Tables[0].Rows)
{
int iId = int.Parse(row["id"].ToString());
}

As you can see you are parsing the id column. You know it's int. But int.Parse can only work on strings, so you are required to turn this object to string, calling its .ToString() method. This will slow down your code insignifficantly on few rows and signifficantly on more rows (few thousands for example).

The following is also wrong:

foreach (DataRow row in dsReportSource.Tables[0].Rows)
{
int iId = Convert.ToInt32(row["id"]);
}

Here you are telling your compiller that you are sure the parameter (row["id"]) will cast to Int32 without problems.
But here you are telling your compiller only 50% of the truth. After you KNOW it is int, just be honest and say:

foreach (DataRow row in dsReportSource.Tables[0].Rows)
{
int iId = (int)row["id"];
}

This applies not only to DataSets but everywhere you have a fixed datatype and you know what the type is.


Don't let your compiler do the work.
Just look at your project and try to find places where you are uncertain about fixed datatype.
Change it to be a direct cast and I am pretty sure you will experience speed improvements.

Why your HttpHandler has the Session set to NULL?

I was in a need to create HttpHandler. I also needed to use the session.
Here is my first attempt:

   public class ChbHandler : IHttpHandler
   {
     #region IHttpHandler Members

     public bool IsReusable
     {
        get { return true; }
     }

     public void ProcessRequest(HttpContext context)
     {
        HttpRequest req = context.Request;
        HttpResponse resp = context.Response;
        resp.Write("HttpHandler: Hello World!");
     }
     #endregion
   }

In Here if you try to use the Session object you will not it is null. Why is that?
I googled a bit and found that in order to support session, your HttpHandler should inherit the

IRequiresSessionState or IReadOnlySessionState in order to have the session state in the context parameter (the one that is passed to the ProcessRequest() routine.
Luckilly both interfaces are just marker interfaces, meaning you are not required to implement any additional methods.
So something like this:

   public class ChbHandler : IHttpHandler, IRequiresSessionState
   {
     #region IHttpHandler Members

     public bool IsReusable
     {
        get { return true; }
     }

     public void ProcessRequest(HttpContext context)
     {
        HttpRequest req = context.Request;
        HttpResponse resp = context.Response;
        resp.Write("HttpHandler: Hello World!");
     }
     #endregion
   }

Should work just fine for you.
The only change is : IRequiresSessionState in the list of Interfaces that the class will inherit.

5 minutes C# - get windows special folders path

Just a two lines of code in order to retrieve the path to a special folder of your choice (My Documents, ApplicationData etc):

string strAppData = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
DirectoryInfo diMyDocuments = new DirectoryInfo(strAppData);

Here is the Environment.SpecialFolder Enum:

Environment.SpecialFolder.ApplicationData - the data which some applications store about the current user (mostly used for personalized settings), this is for roaming users.
Environment.SpecialFolder.CommonApplicationData - Application data which is common for all users.
Environment.SpecialFolder.CommonProgramFiles - "The directory for components that are shared across applications"
Environment.SpecialFolder.Cookies - The folder where the user cookies are stored.
Environment.SpecialFolder.Desktop - The logical desktop.
Environment.SpecialFolder.DesktopDirectory - this is the directory which is used to store file objects on the desktop.
Environment.SpecialFolder.Favorites - Current user favorite items.
Environment.SpecialFolder.History - Current user Internet History.
Environment.SpecialFolder.InternetCache - Internet cached files.
Environment.SpecialFolder.LocalApplicationData - As the first one but for non-roaming users.
Environment.SpecialFolder.MyComputer - I'll let you figure this out ...
Environment.SpecialFolder.MyDocuments - I'll let you figure this out too ...
Environment.SpecialFolder.MyMusic - ... and this one ...
Environment.SpecialFolder.MyPictures - ... and this one ...
Environment.SpecialFolder.Personal - this one is more important, this directory is used as a repository for documents...
Environment.SpecialFolder.ProgramFiles - this one is clear, I believe
Environment.SpecialFolder.Programs - Contains user program groups.
Environment.SpecialFolder.Recent - Users most recently used documetns.
Environment.SpecialFolder.SendTo - This directory is used for the Send To > item in the context menu. By adding folders here, they will appear in the Send To -> item when you click on a file or folder.
Environment.SpecialFolder.StartMenu - Contains the Start Menu items.
Environment.SpecialFolder.Startup - The Startup group (Start Menu -> All Programs -> Startup).
Environment.SpecialFolder.System - The system directory (%Windir%\System32)
Environment.SpecialFolder.Templates - Document templates repository.


Hope I helped a bit.
Have a great coding.

Nice little tool to help me with twitter.

I created a small twitter software what it does is to check each hour if I am listening to Winamp, get the song if possible and write it in twitter for me and the people who are eventually interested in what I am listening.
Here is the deal:



You can download it from here:
TWamp - Nice little twitter software

You can follow me on twitter from the following url:
My twitter profile

Please note: TWamp isn't very user friendly. You need to get along with it in order to use it ;).