ASP.NET Weblogs

Extension Methods Roundup: IndicesWhere, TakeEvery, Distinct

Omer van Kloeten — Sun, 18 May 2008 13:14:21 GMT

As I do from time to time, here is a batch of three Extension Methods I've written recently:

IndicesWhere

/// <summary>
/// Gets the indices where the predicate is true.
/// </summary>
public static IEnumerable<int> IndicesWhere<T>(this IEnumerable<T> enumeration, Func<T, bool> predicate)
{
    // Check to see that enumeration is not null
    if (enumeration == null)
        throw new ArgumentNullException("enumeration");

    // Check to see that predicate is not null
    if (predicate == null)
        throw new ArgumentNullException("predicate");

    int index = 0;

    foreach (T item in enumeration)
    {
        if (predicate(item))
            yield return index;

        index++;
    }
}

This is especially useful when you want to cache indices from an array, rather than the array itself. Here's an example:

var indicesWithValues = values.IndicesWhere(value => value != null);

TakeEvery

/// <summary>
/// Take items from 'startAt' every at 'hopLength' items.
/// </summary>
public static IEnumerable<T> TakeEvery<T>(this IEnumerable<T> enumeration, int startAt, int hopLength)
{
    // Check to see that enumeration is not null
    if (enumeration == null)
        throw new ArgumentNullException("enumeration");

    int first = 0;
    int count = 0;

    foreach (T item in enumeration)
    {
        if (first < startAt)
        {
            first++;
        }
        else if (first == startAt)
        {
            yield return item;

            first++;
        }
        else
        {
            count++;

            if (count == hopLength)
            {
                yield return item;

                count = 0;
            }
        }
    }
}

This is equivalent to an unbounded series of Skip(startAt).Take(1).Skip(hopLength).Take(1).Skip(hopLength)... Useful for when you, for instance, need only every other item in a list.

Distinct

It's really been pissing me off that there's no overload to Distinct that takes a delegate, which means I have to write a new class whenever my comparison isn't the default one. When talking about Anonymous Types, Distinct becomes useless. So here's an overload I can actually use:

private class EqualityComparer<T> : IEqualityComparer<T>
{
    public Func<T, T, bool> Comparer { get; internal set; }
    public Func<T, int> Hasher { get; internal set; }

    bool IEqualityComparer<T>.Equals(T x, T y)
    {
        return this.Comparer(x, y);
    }

    int IEqualityComparer<T>.GetHashCode(T obj)
    {
        // No hashing capabilities. Default to Equals(x, y).
        if (this.Hasher == null)
            return 0;

        return this.Hasher(obj);
    }
}

/// <summary>
/// Gets distinct items by a comparer delegate.
/// </summary>
public static IEnumerable<T> Distinct<T>(this IEnumerable<T> enumeration, Func<T, T, bool> comparer)
{
    return Distinct(enumeration, comparer, null);
}

/// <summary>
/// Gets distinct items by comparer and hasher delegates (faster than only comparer).
/// </summary>
public static IEnumerable<T> Distinct<T>(this IEnumerable<T> enumeration, Func<T, T, bool> comparer, Func<T, int> hasher)
{
    // Check to see that enumeration is not null
    if (enumeration == null)
        throw new ArgumentNullException("enumeration");

    // Check to see that comparer is not null
    if (comparer == null)
        throw new ArgumentNullException("comparer");

    return enumeration.Distinct(new EqualityComparer<T> { Comparer = comparer, Hasher = hasher });
}

I'll be integrating these methods into the Linq Extensions project soon enough. Good hunting. :)

Cloning objects in .NET

Edgar Sánchez — Sun, 18 May 2008 06:27:38 GMT

In an interesting project where I'm giving a hand, we need to clone objects of a number of different types, perhaps surprisingly the CLR doesn't offer a general cloning method, of course you could use MemberwiseClone() but this is a protected method, so it can be invoked only from inside the class of the object being cloned, which makes it difficult to use it in a general method, besides, MemberWiseClone() does just a shallow copy and what we really need is a deep copy.

There is a good reason for not having such a general method: object cloning is one of those problems which have a simple solution for simple scenarios but that resist a satisfactory solution for all the scenarios, for example the objects may have references to other objects and even to themselves be it directly or after a long chain, for example a customer has invoices that have payments that refer to the customer, a general cloning algorithm for a web several times more complex than that is anything but trivial. But the need of moving objects (and their web) is inescapable in distributed environments, because you have to move the invoices and the customers from the business layer to the presentation layer, so there are indeed mechanisms, albeit with some limitations, for serializing and deserializing object graphs, with the help of these mechanisms we can try and build a general object cloner:

    1 
    2     public static T BinaryClone<T>(this T originalObject)
    3     {
    4         using (var stream = new System.IO.MemoryStream())
    5         {
    6             var binaryFormatter = new System.Runtime.Serialization.Formatters.Binary.BinaryFormatter();
    7             binaryFormatter.Serialize(stream, originalObject);
    8             stream.Position = 0;
    9             return (T)binaryFormatter.Deserialize(stream);
   10         }
   11     }
   12 

We just convert, using as intermediary a memory stream, our object to a bit string and then we synthesize a *new object* from that bit string. The use of BinaryClone() flows nicely:

    1 
    2     var clone = person.BinaryClone();
    3 

Easy to write, but we have to be careful of the performance and the corner cases. I run a few *very informal* performance tests with this object:

    1 
    2     var person = new Person
    3     {
    4         Id = 101,
    5         Name = "Sánchez, Sebastián",
    6         Salary = 590.20m,
    7         BirthDate = new DateTime(2000, 6, 15),
    8         Address = new Address { Number = "N24-78", Street = "Pasaje Córdova" }
    9     };
   10 

And I found that doing a hundred thousand clones takes some nine thousand milliseconds, that is each cloning takes less than one ten-thousandth of a second, which is adequate to our needs. BinaryFormatter has been with us since .NET Framework 1.0 so I'm not like saying anything even remotely new or unknown, but tomorrow (or the day after, or the day after...) I'll talk about a small refinement to BinaryClone().

New Article: Images as a Service with ADO.NET Data Services

Nullable — Sun, 18 May 2008 02:01:00 GMT

For those of you who have already put your feet into the waters of .NET 3.5 SP1, you have probably seen some amazing things with ADO.NET Data Services coupled to the Entity Framework. But that coupling may lead to blindness. Allow me to explain.

[continue to article: Images as a Service with ADO.NET Data Services]

Interesting Finds: 2008.05.18

gOODiDEA — Sun, 18 May 2008 01:49:57 GMT

Debug

.NET

Web

Javascript Tutorial - Continuous Pagination
20 Useful Tools to Make Web Development More Efficient
Mojax - a mobile Ajax application framework

Other

"Swapping" instead of "Injecting" calls between classes

RoyOsherove — Sun, 18 May 2008 01:01:15 GMT

Eli Lopian, Typemock CEO and awesome Coder, just created a nice little API wrapper around Typemock Isolator that would allow a very simple and readable "Swapping" effect between classes. It would allow you to write code like this:

    [Test]
       public void SwapStatic_CallsFake()
       {
           Swap.StaticCalls<TypeA, TypeB>(); 
           Assert.AreEqual(2, TypeA.StaticReturnOne()); 
           Swap.Rollback();
       }
 
       [TestMethod]
       public void SwapInstance_CallsFake()
       {
           Swap.NextNew<OriginalClass, FakeClass>();
           OriginalClass swappedInstance = new OriginalClass();
           Assert.AreEqual(2, swappedInstance.ReturnOne());
       }

The first test uses the "Swap" class to replace static calls and redirect them to your own class with static methods. The second one is more advanced and will mock all instance calls made on the next instance that will be created of that type. so the last line on the second test will actually call a method against the FakeClass type.

pretty cool and very readable. download the code and binaries from his post.

Enterprise Library 4.0 Released

HosamKamel — Sat, 17 May 2008 15:39:18 GMT

Enterprise Library is a collection of application blocks intended for use by developers who build complex, enterprise-level applications. Enterprise Library is used when building applications that are typically to be deployed widely and to interoperate with other applications and systems. In addition, they generally have strict security, reliability, and performance requirements.

The goals of Enterprise Library are the following:

Consistency. All Enterprise Library application blocks feature consistent design patterns and implementation approaches.
Extensibility. All application blocks include defined extensibility points that allow developers to customize the behavior of the application blocks by adding their own code.
Ease of use. Enterprise Library offers numerous usability improvements, including a graphical configuration tool, a simpler installation procedure, and clearer and more complete documentation and samples.
Integration. Enterprise Library application blocks are designed to work well together or individually.

These are typically rationalized through:

Online Guidance
Scenarios or QuickStart samples
QuickStart Walkthroughs
Hands-On Labs
Sample Source Code

There will be a webcast in June 2008 giving an overview of the new features of Enterprise Library 4.0. You can find more detail on the Enterprise Library landing page.

What's New

This release of Enterprise Library includes the following:

Integration with the Unity Application Block
Windows Management Instrumentation (WMI) 2.0 support and improved instrumentation
Performance improvements (particularly, in the Logging Application Block)
Pluggable Cache Managers
Visual Studio 2008 support
Bug fixes

Note: existing public APIs (v3.1) are still supported.

Links

MSDN site: http://msdn.microsoft.com/entlib
Community Forum: http://go.microsoft.com/fwlink/?LinkID=119312
Community Extensions: http://codeplex.com/entlibcontrib

VIA : Mike Walker's Blog

.NET Framework 1.1 Service Pack 1 and Page.RegisterStartupScript

AGS777 — Sat, 17 May 2008 12:36:00 GMT

First, if you are are developing exclusively ASP.NET 2.0+ applications, sorry, there is nothing interesting for you in this post.

Second, if you are involved in some ASP.NET 1.1 projects and have no plans to install new development environment, then, sorry again, there is probably no reason for you to read on either. Ok, I've done all I could to warn you against reading it. Don't blame me for wasting you time, because I am going to start from the very beginning.

One of my current projects is ASP.NET 1.1 Web Application. It is already released and rather stable. And yesterday I got new development machine on my workplace and migrated all my data to it. .NET Frameworks 1.1, 2.0, 3.0, 3.5 were preinstalled before I first logged in (thanks to our system administrators). I installed VS 2003 and SP1 for it, VS 2008, SVN client, some other necessary utilities and components. Then, updated sources from source control for the mentioned ASP.NET 1.1 Web Application and started it. Bang! Script error - some variable is undefined.

Actually there were a bunch of such errors on the page. As I intentionally mentioned earlier, the application is stable. And this particular page was not changed for quite some time.

Brief research of the generated HTML source, code-behind class and respective web controls revealed the cause of the exception: there was a sequence of similar Page.RegisterStartupScript statements which went in pairs. The first one in a pair registered some JavaScript object, and the second one - used the object in another declaration.

First I checked source control's log - no related changes. Then, the next suspect - application configuration changes that could cause such behavior. But no, all the related controls' declarations on the page are static.

Ok, code was not changed, application is working fine on QA environment. So, something is wrong with my new machine. But what?

I had a dim recollection that there is something wrong with the sequence of script registration in ASP.NET 1.1. But common sense told me that if something wrong could happen then it would had happened long ago.

Still, I opened Reflector and found such code inside RegisterScriptBlock method of System.Web.UI.Page class:

     if (scriptBlocks == null)
    {
        scriptBlocks = new HybridDictionary();
    }

As you probably well aware of, HybridDictionary changes its internal storage from ListDictionary to Hashtable starting from its ninth element. So, of course we cannot rely on any specific order of script registrations if script blocks are stored in HybridDictionary. But how did it work earlier and how the same code works on development server and QA environment without any bugs reported?

So, I copied Reflector to the development server and found following code in the same RegisterScriptBlock method that I reviewed on my machine:

    if (scriptBlocks == null)
    {
        scriptBlocks = new ListDictionary();
    }

The code was fixed. But where did the fix come from? I recalled that there is a service pack for .NET 1.1 that I installed on my old development machine several years ago. Google promptly gave me a link.

File name: NDP1.1sp1-KB867460-X86.exe, Version: 1, Date Published: 8/30/2004, Download Size: 10.2 MB

Why am I presenting all this information here? Because the fix did not help, though I was almost certain that it should. The same HybridDictionary.

That's was fiasco. My working day was over several hours ago. Finish.

But today I decided to reproduce the issue at home. Fortunately I had a virtual machine with Windows XP and fortunately the copy of .NET 1.1 System.Web.dll had the same version as the one at work (i.e. HybridDictionary is used in RegisterScriptBlock).

So I started googling again and found the second service pack. Strangely enough it has the same name (i.e. .NET Framework 1.1 Service Pack 1) though with a lengthy suffix (.NET Framework 1.1 Service Pack 1 SYSTEM.WEB.DLL and MSCOREE.DLL Security Update for Windows 2000, Windows XP, Windows 2003 Server x64/IA64 and Windows 2003 Server R2 x64/IA64) .

Like the previous service pack that I found, description for this one states that its purpose - security improvements. No mentions of ASP.NET-specific modifications. I could not find any documentation which describes the changes in detail.

But the main thing is that this second "Service Pack 1" done what I wanted. Eventually I had my ListDictionary back.

The summary is:

1) there are at least TWO patches called ".NET 1.1 Service Pack 1";

2) both of them state that they are focused on security improvements, but

3) one of them changes at least one fundamental aspect of ASP.NET 1.1 behavior.

Thank you for reading. Good luck.

Note on Customizing Content Query Web Part

Colt — Sat, 17 May 2008 03:05:00 GMT

Content Query Web Part (CQWP) is a powerful feature in SharePoint, where users can create custom view of data that is queried from various sources, lists, libraries, and present all in one web part. One of my tasks yesterday is to create a content query web part, and query the contents from two sub-sites. Specifically, I have 2 calendars in 2 sub-sites and I have to query all events and combine into a master calendar in the top site (Of course I can make use of the great filtering, sorting and grouping features in CQWP).

After adding the CQWP, my next step is to customize the layout because the default one is too plain. I google and find all these useful articles:

One of the techniques in customizing CQWP layout is to make use of internal field name and modify CommonViewFields in the exported .webpart file. I follow all steps, modify the .webpart and xsl files as I wish, but I still can't display the content in my CQWP (I can see some other default fields like Title though).

Later, I find the bug is at the key element - CommonViewFields - It does not allow SPACE in the value string. For example:

Wrong: <property name="CommonViewFields" type="string">Title, Text; Description, Note;</property>

Correct: <property name="CommonViewFields" type="string">Title,Text;Description,Note</property>

My note is that we developers cannot add SPACE when typing the value, or even anywhere in the tag. And, we should not add a semi-colon at the end of the string.

P.S. After customizing the layout and fields on the CQWP, we will most probably need to format the field, such as changing the time format of a DateTime field, number of decimal points etc, and here is a very useful reference article: Customizing the Content Query Web Part XSL

ASP.NET and Images on a Network Share

du8die — Sat, 17 May 2008 01:58:00 GMT

The school district I work for had an idea for an application. The need comes from several angles. First of all, lunch counts are all done by paper. Attendance is taken on paper, then it is sent to the Health Room, where tallies are made, and then everything is recorded into our Student Management System (SMS for short), and our Food Service app. Most (if not all) of our elementary class rooms will have Smart Boards next year. So we decided to write an app that would allow the students to "check in" in the morning on the smart board. The kids can go up to the board and select their lunch choice, and do attendance all at once.

Getting the app to work was the easy part. Our SMS keeps all of the students photos on a drive. I wanted to use those photos directly off of the SMS server, rather than copy them locally. So, I shared the folder that contained the pictures. Then I mapped a drive on the server, and voila. Everything didn't work.

Apparently, there are security restrictions that prevent a web app from using files on a network share. It took a lot of iterations to get where I wanted. I can post details if of the process if need-be.

Here's what I ended up with.

In SQL 2005, there is a little gem. OpenRowSet.

SELECT BulkColumn as 'Photo' FROM OPENROWSET(BULK N'p:\test.jpg', SINGLE_BLOB) AS Photo

This returns a single column with blob datatype. So, I can then bring it into an image handler and go crazy.

Well, I mapped my drive, and then ran that command, and got an access denied error. I realized that SQL Server runs under the local system account ("NT AUTHORITY\SYSTEM"). The mapped drive didn't exist under that identity. So, I then found a reference somewhere (I forget the link) that says you can map a drive to the system account if you schedule a command to run with the AT command.

So, I created a batch file that mapped the drive with the remote machine's authentication:

net use p: \\10.10.xx.xx\pics remotemachinepassword /user:remotemachinename\remotemachineuser

Then, I scheduled the AT command to run the batch file:

at 20:00 c:\mapit.bat

This forced the system local account to have the mapped drive. I then ran my SQL in my app that pulled the images over, and PERFECT!

So, using a little SQL Server magic and a mapped drive to the system local user, you can in fact, use a resource from a remote machine in an ASP.NET app.

I want to test the mapped drive without the SQL Server stuff. I'll get to that on Monday.

Winforms on Linux - Mono 2.0 Winform API is complete(?)

zroiy — Fri, 16 May 2008 22:33:00 GMT

So looks like that the Mono project has reached a significant milestone by completing all of its Winform 2.0 API.
And it encouraged me to get back into evaluating Mono's progress. A while back, I was disappointed that the rich text box component not functioning well, actually back than it simply crashed.
I wanted to check out whether Mono has made good progress with it. So I fired up my VMWare Suse machine , checked the mono version there - it was an early version (1.2.5) . looks like it was a while back since I've touched it.
Installing the 1.9 version was pretty easy, just download it from the mono site, switched to root user by executing 'sudo su' on a terminal window, and then running the trivial installation commands

tar -jxvf mono-1.9.1.tar.bz2
cd mono-1.9.1
./configure
make
make install

/usr/local/bin/mono -version -> shows you that you've got the right version
BTW, if you're downloading the VMWare image from the link above , it is already preinstalled with the 1.9.1 version

Next I've created a simple Winforms application on Visual Studio 2005 on my windows box (which is also the host of my linux suse virtual machine), it is a simple winform with a RichTextBox component and a button that opens up a file dialog.

I've tested it by opening a simple rtf file.

which includes both free text and an image.

Next, I needed to move my compiled winform.exe file to the suse virtual machine side. The easiest way to do this is to make sure there is a network connection between the virtual machine (guest) and the host machine and use the smbclient command to connect to the host machine folder from the virtual machine.

Here is a simple command line
smbclient -w domain -user username \\[remote ip] password
this is what I used
smbclinet -w domain -user user1 \\\\192.168.1.2\\share my_password

within the smbclient application you can use the following commands (which resembles ftp commands)

cd - change remote directory
lcd - change local directory
get - get a file
dir - list remote directory content

So I got my rtf_window.exe and the sample rtf from my host machine into my virtual linux box, executed the application , loaded up the rtf file and this is what I got.

Reminder , this is how it should look like

Looks like some of the font properties are missing and images are not supported at all.

Overall it looks like that the Mono guys have done a really good job in providing a real cross platform alternative , but there's just this nagging RichTextBox thing..
Hey Mono guys, if you can fix this that would be great...

(could it be that images are stored as BMP which is Microsoft's IP ?)

Update : using the latest stack (mono-103389.tar.bz2 and libgdiplus-101878.tar.bz2 ) doesn't help either