OmegaMan's Musings

Sometimes in C# .Net (see Notes section on usage for before .Net 4)  one might have a list of items and want to make them into pairs. Possibly to take those pairs and place the them into a dictionary. If the items are in a list, that list is linear by nature and using linq is not an option when using the extension ToDictionary.

I have created extension methods to create paired values from any list and those methods are named AsPairs and AsPairsSafe. If the list is odd in length, the final number will be combined with the system default for that type as handled in the method AsPairs. If that is not desired then call AsPairsSafe which will skip the last odd value.

Here is the usage of the AsPairs extension on integers and strings:

var ints = new List<int> { 1, 2, 3, 4, 5 };

IEnumerable<Tuple<int,int>> asTuplePairs = ints.AsPairs();

/* asTuplePairs looks like this(Note value 5 is paired with a default value of 0)
1,2 
3,4
5,0
*/

var strings = new List<string> { "Alpha", "Beta", "Gamma", "Delta", "Omega" };

IEnumerable<Tuple<string,string>> asTuplePairsStrings = strings.AsPairs();

/* asTuplePairsStrings (note Omega is paired a default value of Null)
Alpha, Beta 
Gamma, Delta
Omega, NULL

Whereas the call to AsPairsSafe would return without Omega:
Alpha, Beta 
Gamma, Delta
*/

Here are the extension methods:

public static class MyExtensions
{
   // Create Pairs from a list. If the list is odd add a default value for the final pair. 
   public static IEnumerable<Tuple<T, T>> AsPairs<T>(this List<T> list)
   {
      int index = 0;

      while (index < list.Count())
      {
         if (index + 1 > list.Count())
            yield break;

         if (index + 1 == list.Count())    
            yield return new Tuple<T,T>(list[index++],  default(T));
         else
            yield return new Tuple<T,T>(list[index++],  list[index++]);
      }
   }

   // Create Pairs from a list. Note if the list is not even in count, the last value is skipped.
   public static IEnumerable<Tuple<T, T>> AsPairsSafe<T>(this List<T> list)
   {
      int index = 0;

      while (index < list.Count())
      {
         if (index + 1 >= list.Count())
            yield break;

         yield return new Tuple<T,T>(list[index++],  list[index++]);
      }

   }
}

Notes

Tuple is a .Net 4 item. If you are using a previous version of .Net use the KeyValuePair structure instead.

One of the basic tenets of WYSIWYG is to be able to create a rubber band region using the mouse to give the user the ability to create a selectable region. This article demonstrates how to do that in any version of Silverlight and the user is given the tools to create such a bounding rectangle in any circumstances via the usage of some basic building blocks in Silverlight.

The below picture (not the one on the left) shows our goal, the dynamic creation of a bounding rubber band (a rectangle control for this demonstration) in a canvas. The below canvas is drawn in black (visually grey due to the opacity set) while the bounding rectangle shows itself in red.

The user starts the process with an initial click which designates a start location of an upper left point for our bounding box with a mouse click.  Once the click happens the mouse cursor changes to a hand (if moving to the lower right) as a visible indicator that the process has started. While user continues to move to the lower right the band grows and while the mouse button has yet to be let go or released. For the demo a bounded number is shown is which relates the actual dynamic change in the X (horizontal) position. That is done for this article only and the above picture shows the rectangle with an X size of 123 pixels and can still be grown as shown by the hand icon.

Initial Xaml

In the page’s xaml we add a grid and a canvas as such this:

<Grid x:Name="LayoutRoot" Background="White">
    <Grid.RowDefinitions>
        <RowDefinition Height="33*" />
        <RowDefinition Height="267*" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="32*" />
        <ColumnDefinition Width="568*" />
    </Grid.ColumnDefinitions>
    <Canvas x:Name="cMain"
            MouseLeftButtonDown="cMain_MouseLeftButtonDown"
            MouseLeftButtonUp="cMain_MouseLeftButtonUp"
            MouseMove="cMain_MouseMove"
            Grid.Row="1"
            Grid.Column="1">
        <TextBlock Width="100"
                    Height="30"
                    Text="{Binding XValue, ElementName=userControl}"
                    />
        <Rectangle Fill="Black"
                    Width="550"
                    Height="200"
                    Opacity=".25"/>
    </Canvas>
</Grid>

The things to note are that the canvas is in a grid which is offset from the initial by 30 pixels in both axis. We then place a rectangle on the canvas which is our area which will be our strike zone where we will intercept the messages mouse events. We have a strike zone because individual controls in a canvas, such as texblocks have whitespace between them and the canvas will not get the mouse clicks and we want to be able to capture the process at all locations on the canvas; hence we fill up the canvas with our strike zone as to be ensured that the events are consumed properly by the code. 

When the user clicks within the strike zone the process starts as signified by a cursor change to the hand, as the user moves within the zone the rubber banding increases and when the mouse button is let up the process ends and the cursor is returned to its previous state.

Initial Properties

Here are the three variables we will use during this process:

private int _xValue;

public int XValue
{
    get { return _xValue; }
    set
    {
        _xValue = value;
        OnPropertyChanged( "XValue" );
    }
}

private Point OriginatingPostionOnCanvas { get; set; }

private Rectangle RubberBandBox { get; set; }

Since the XValue property is reflected on the screen in a text box it reports all changes by using  INotifyPropertyChanged which our class handles in a standard way for notify property (not shown). Followed by that is our initial click location named OriginatingPostionOnCanvas which will dictate the upper left (or lower right) location of the rubber band rectangle which we will dynamically create. The last variable is the actual dynamic rectangle control named RubberBandBox which will be created and modified during the process.

Event Mouse Left Button Down

We will handle three events during this process. The first is the when the user clicks and begins to hold down the mouse button:

private void cMain_MouseLeftButtonDown( object sender, MouseButtonEventArgs e )
{
    OriginatingPostionOnCanvas = e.GetPosition( cMain );

    RubberBandBox = new Rectangle() { Width = 1, 
                                      Height = 1, 
                                      Fill = new SolidColorBrush( Colors.Red ), 
                                      Opacity = .1
                                    };

    RubberBandBox.SetValue( Canvas.LeftProperty, OriginatingPostionOnCanvas.X);
    RubberBandBox.SetValue( Canvas.TopProperty,  OriginatingPostionOnCanvas.Y );

    cMain.Children.Add( RubberBandBox );
}

Our goals here are simple:

1. Get and store the location where the user clicked in relation to the canvas.
2. Create  and store the rectangle in red and with an opacity which does allows the user to see what is being selected.
3. Setting the initial location of the rectangle and adding it to the children of the canvas.

Event Mouse Move

The user is moving and we must adjust the rectangle as appropriate for the target direction. Note we also have to handle when the user moves to the upper left instead of the lower right…. So when that happens we will change the cursor to a Stylus (the dot) for visual indication that we are getting a reverse band situation.

private void cMain_MouseMove(object sender, MouseEventArgs e)
{
    if (RubberBandBox == null)
        return;

    Point pointMovedTo = e.GetPosition( cMain );

    double xDelta = pointMovedTo.X - OriginatingPostionOnCanvas.X;
    double yDelta = pointMovedTo.Y - OriginatingPostionOnCanvas.Y;

    LayoutRoot.Cursor = ((xDelta > 0) && (yDelta > 0)) ? Cursors.Hand : Cursors.Stylus;

    if (LayoutRoot.Cursor == Cursors.Hand)
    {
        RubberBandBox.Height = yDelta;
        RubberBandBox.Width  = xDelta;
    }
    else if (LayoutRoot.Cursor == Cursors.Stylus)
    {
        RubberBandBox.Height = Math.Abs( yDelta );
        RubberBandBox.Width = Math.Abs( xDelta );

        if (xDelta < 0)
            RubberBandBox.SetValue( Canvas.LeftProperty, pointMovedTo.X );

        if (yDelta < 0)
            RubberBandBox.SetValue( Canvas.TopProperty, pointMovedTo.Y );
    }

    XValue = (int) (e.GetPosition( cMain ).X - OriginatingPostionOnCanvas.X);
}

Event Mouse Left Button Up

This is our final event we have to handle. We do a safety check on whether we are actually in operations, and if we are then we simply return the cursor to its original state and remove the rectangle from the canvas’ children.

private void cMain_MouseLeftButtonUp( object sender, MouseButtonEventArgs e )
{
    if (RubberBandBox == null)
        return;

    // Return to the previous state; whatever it is, the OS handles it.
    LayoutRoot.Cursor = null; 

    cMain.Children.Remove( RubberBandBox );

    // Show that we are not processing by making this null.
    RubberBandBox = null; 
}

Most of the time one needs the power of the xml parser whether it is the XmlDocument or Linq to Xml to manipulate and extract data. But what if I told you that in some circumstances regular expressions might be faster?

Most conventional development thinking has branded regex processing as slow and the thought of using regex on xml might seem counter intuitive. In a continuation of articles I again want to dispel those thoughts and provide a real world example where Regular Expression parsing is not only on par with other tools in the .Net world but sometimes faster. The results of my speed test may surprise you;  and hopefully show that regular expressions are not as slow as believed, if not faster!

See: Are C# .Net Regular Expressions Fast Enough for You?

Real World Scenario

There was a developer on the MSDN forums who needed the ability to count URLs in multiple xml files. (See the actual post count the urls in xml file on Msdn) The poster received three distinct replies, one to use XMLDocument, another provided a Linq to XML solution and I chimed in with the regular expression method. The poster took the XMLDocument method and marked as the answer, but could he have done better?

I thought so…

So I took the three replies and distilled them down into their core processing and wrapped them in a similar IO extraction layer and proceeded to time them. I created 48 xml files with over one hundred thousand urls to find for a total of 13 meg on disk. I then proceeded to run the test all in release mode to get the results.  (See below section Setup to get a gist repository of the code).

Real World Result

Five tests, each test name is the technology and the user as found on the original msdn post. In red is the slowest and fastest time. Remember XmlDoc is the one the user choose as the answer.

Test 1
Regex           found 116736 urls in 00:00:00.1843576
XmlLinq_Link_FR found 116736 urls in 00:00:00.2662190
XmlDoc_Hasim()  found 116736 urls in 00:00:00.3534628

Test 2
Regex           found 116736 urls in 00:00:00.2317883
XmlLinq_Link_FR found 116736 urls in 00:00:00.2792730
XmlDoc_Hasim()  found 116736 urls in 00:00:00.2694969

Test 3
Regex           found 116736 urls in 00:00:00.1646719
XmlLinq_Link_FR found 116736 urls in 00:00:00.2333891
XmlDoc_Hasim()  found 116736 urls in 00:00:00.2625176

Test 4
Regex           found 116736 urls in 00:00:00.1677931
XmlLinq_Link_FR found 116736 urls in 00:00:00.2258825
XmlDoc_Hasim()  found 116736 urls in 00:00:00.2590841

Test 5
Regex           found 116736 urls in 00:00:00.1668231
XmlLinq_Link_FR found 116736 urls in 00:00:00.2278445
XmlDoc_Hasim()  found 116736 urls in 00:00:00.2649262

Wow! Regex consistently performed better, even when there was no caching of the files as found for the first run! Note that the time is Hours : Minutes : Seconds and regex’s is the fastest at 164 millseconds to parse 48 files! Regex worst time of 184 milleseconds is still better than the other two’s best times.

How was this all done? Let me show you.

Setup

Ok what magic or trickery have I played? All tests are run in a C# .Net 4 Console application in release mode. I have created a public Gist (Regex vs Xml) repository of the code and data which is actually valid Git repository for anyone how may want to add their tests, but let me detail what I did here on the blog as well.

The top level operation found in the Main looks like this where I run the tests 5 times

Enumerable.Range( 1, 5 )
            .ToList()
            .ForEach( tstNumber =>
            {
                Console.WriteLine( "Test " + tstNumber );
                Time( "Regex", RegexFindXml );
                Time( "XmlLinq_Link_FR", XmlLinq_Link_FR );
                Time( "XmlDoc_Hasim()", XmlDoc_Hasim );
                Console.WriteLine( Environment.NewLine );
            }

while the Time generic method looks like this and dutifully runs the target work and reports the results in “Test X found Y Urls in X [time]”:

public static void Time<T>( string what, Func<T> work )
{
    var sw = Stopwatch.StartNew();
    var result = work();
    sw.Stop();
    Console.WriteLine( "\t{0,-15} found {1} urls in {2}", what, result, sw.Elapsed );
}

Now in the msdn post the different methods had differing ways of finding each xml file and opening it, I made them all adhere to the way I open and sum the ULR counts. Here is its snippet:

return Directory.EnumerateFiles( @"D:\temp", "*.xml" )
            .ToList()
            .Sum( fl =>
            {

            } );

Contender  –  XML Document

This is one which the poster marked as the chosen one he used and I dutifully copied it to the best of my ability.

public static int XmlDoc_Hasim()
{
    return Directory.EnumerateFiles( @"D:\temp", "*.xml" )
                .ToList()
                .Sum( fl =>
                {
                    XmlDocument doc = new XmlDocument();
                    doc.LoadXml( System.IO.File.ReadAllText( fl ) );

                    if (doc.ChildNodes.Count > 0)
                        if (doc.ChildNodes[1].HasChildNodes)
                            return doc.ChildNodes[1].ChildNodes.Count;

                    return 0;

                } );

}

I used the sum extension method which is a little different from the original sum operation used, but it brings the tests closer in line by using the Extension.

Contender – Linq to Xml

Of the other two attempts, this one I felt was the more robust of the two, because it actually handled the xml namespace. Sadly it appeared to be ignored by the original poster. Here is his code

public static int XmlLinq_Link_FR()
{
    XNamespace xn = "http://www.sitemaps.org/schemas/sitemap/0.9";

    return Directory.EnumerateFiles( @"D:\temp", "*.xml" )
                    .Sum( fl => XElement.Load( fl ).Descendants( xn + "loc" ).Count() );

}

Contender – Regular Expression

Finally here is the speed test winner. I came up with the pattern design Upon by looking at the xml and it appeared one didn’t need to match the actual url, but just the two preceding  tags and any possible space between. That is the key to regex, using good patterns can achieve fast results.

public static int RegexFindXml()
{
    string pattern = @"(<url>\s*<loc>)";

    return Directory.EnumerateFiles( @"D:\temp", "*.xml" )
                    .Sum( fl => Regex.Matches( File.ReadAllText( fl ), pattern ).OfType<Match>().Count() );

}

XML1 (Shortened)

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url><loc>http://www.linkedin.com/directory/companies/internet-web2.0-startups-social-networking/barcelona.html</loc><changefreq>weekly</changefreq></url>
<url><loc>http://www.linkedin.com/directory/companies/internet-web2.0-startups-social-networking/basel.html</loc><changefreq>weekly</changefreq></url>
<url><loc>http://www.linkedin.com/directory/companies/internet-web2.0-startups-social-networking/bath.html</loc><changefreq>weekly</changefreq></url>
<url><loc>http://www.linkedin.com/directory/companies/computer-networking/sheffield.html</loc><changefreq>weekly</changefreq></url>
<url><loc>http://www.linkedin.com/directory/companies/computer-networking/singapore.html</loc><changefreq>weekly</changefreq></url>
<url><loc>http://www.linkedin.com/directory/companies/computer-networking/slough.html</loc><changefreq>weekly</changefreq></url>
<url><loc>http://www.linkedin.com/directory/companies/computer-networking/slovak-republic.html</loc><changefreq>weekly</changefreq></url>
</urlset>

Xml2 Shortened

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url><loc>http://www.linkedin.com/groups/gid-2431604</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2430868</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/Wireless-Carrier-Reps-Past-Present-2430807</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2430694</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2430575</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2431452</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2432377</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2428508</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2432379</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2432380</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2432381</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2432383</loc><changefreq>monthly</changefreq></url>
<url><loc>http://www.linkedin.com/groups/gid-2432384</loc><changefreq>monthly</changefreq></url>
</urlset>

Summary

It really comes down to the right tool for the right situation and this one regex really did well. But Regex is not good at most xml parsing needs, but for certain scenarios it really shines. If the xml has malformed or the namespace was wrong, then the parser has its own unique problems which would lead to a bad count. All the technologies had to do some upfront loading and that is key to how they performed. Regex is optimized to handle large data efficiently and as long as the pattern is spot on, it can really be quick.

My thought is don’t dismiss regular expression parsing out of hand, while the learning of it can pay off in some unique text parsing situations.

This is related to my presentation tonight (July 25, 2011) at the Denver Visual Studio User’s Group on Effective Silverlight 5 Development.

Links

• Materials (Demo’s Power Point etc).
• Blend Training
• Sketchflow Template for Windows Phone

RitchTextBox OverflowContentTarget Example

<StackPanel Width="400"
            VerticalAlignment="Top"
            Orientation="Horizontal">

    <RichTextBox x:Name="rtbPrimary"
                 Width="80"
                 Height="100"
                 Margin="5,10,0,0"
                 HorizontalScrollBarVisibility="Disabled"
                 VerticalScrollBarVisibility="Disabled"
                 OverflowContentTarget="{Binding ElementName=rtbOverflow}">
        <Paragraph>
            The Denver Visual Studio User's group is overflowing at 100 people! Come early to get a seat.
        </Paragraph>
    </RichTextBox>

    <RichTextBoxOverflow Width="200"
                         Height="100"
                         Margin="5,10,0,0"
                         HorizontalScrollBarVisibility="Disabled"
                         VerticalScrollBarVisibility="Disabled"
                         x:Name="rtbOverflow" />

</StackPanel>

HTML 5 Canvas

<!DOCTYPE html>
<title>Canvas Shapes and Sizes</title>
    <script type="text/javascript">
        window.onload = function () {
            var canvas = document.getElementById('cvPrimary');
            var ctx = canvas.getContext("2d");

            //Draw a rectangle
            ctx.fillStyle = 'Red';
            ctx.fillRect(10, 20, 50, 50);

            //Draw a circle
            ctx.arc(50, 150, 50, 0, 2 * Math.PI, false);
            ctx.fillStyle = 'Green';
            ctx.fill();

            //Draw an arc
            ctx.beginPath();
            ctx.arc(80, 280, 50, 0, Math.PI, false);
            ctx.fillStyle = 'Navy';
            ctx.fill();

            //Draw lines
            ctx.beginPath();
            ctx.moveTo(50, 350);
            ctx.lineTo(0, 450);
            ctx.lineTo(100, 450);
            ctx.lineTo(50, 350);
            ctx.strokeStyle = 'Orange';
            ctx.lineWidth = 4;
            ctx.stroke();
            ctx.fillStyle = 'Yellow';
            ctx.fill();
        };
</script>

<canvas id="cvPrimary" width="800" height="600"/>

Siverlight Extension

<navigation:Page xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk"
           x:Class="EffectiveSilverlight.Views.ExtensionOverview"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
           xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
           xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
           xmlns:dvsug="clr-namespace:EffectiveSilverlight.Views"
           mc:Ignorable="d"
           xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
           d:DesignWidth="640" d:DesignHeight="480"
           Title="ExtensionOverview Page">
    <StackPanel>
        <sdk:Label Margin="10,10,0,0"
                   FontSize="14"
                   FontFamily="Georgia"
                   FontWeight="Bold"
                   Content="{dvsug:DenverVSUG}"
                    />
    </StackPanel>
</navigation:Page>

using System.Xaml;

namespace EffectiveSilverlight.Views
{
    public class DenverVSUGExtension : IMarkupExtension<string>
    {

        public string ProvideValue(IServiceProvider serviceProvider)
        {

            return "88 people saw William Wegerson discuss Effective Silverlight";

        }

    }
}

This article describes one way to handle asynchronous or async calls in .Net 3.5 or .Net 4.0 when using WCF in Silverlight in C#. The goal is to have a final operation wait for all the calls to finish so to combine all the data gathered, all in a thread safe way. A secondary goal is to minimize the consumer code required to perform this operation from what is currently available in straight WCF async calls.

This article has a short shelf life because after .Net 4 (see What’s Next in C#? Get Ready for Async!) one will use the built in Asynchrony methodology developed. Until that time if one is using any version of Silverlight and WCF then this article describes how to handle those multiple async calls and join the data in a final method call.

Final Result Example

Before delving into the solution, here is how the consumer will use the methodology. Below a user is getting account information of user requests, departments and accounts to join all the data on the view model in the final method for display on a Silverlight page. Thesee operations as shown are setup when the view model class (MyViewModel) is created and no blocking occurs keeping UI thread clear.

public MyViewModel()
{
    DataContext = new MyServiceClient();

    FinalAsync(CombineDataAndDisplay); // When all the data is retrieved, do this method to combine the data From the 3 async callls below

    // Provide the operation as a lambda (could be a method call) to assign data to our target backing store property
    // and if all has gone well (no errors in other async calls) and it is the final completing operation. Do the final
    // Processing call automatically.
    DataContext.GetUserRequestsCompleted   += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _UserRequests, "Acquisition failure for User Requests");};
    DataContext.GetAccountsCompleted       += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _Accounts, "Acquisition Failure for Accounts"); };
    DataContext.GetDepartments             += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _Departments, "Failed to get Department Info."); };   

    // Start the Async processes 
    MultipleAsyncRun(DataContext.GetUserRequestsAsync);
    MultipleAsyncRun(DataContext.GetAccountsAsync);
    MultipleAsyncRun(DataContext.GetDepartmentsAsync);

    // Exit out and return the UI thread to the user operations.
}

// Once all the data is done, combine and assign into our
// PagedCollectionView property for display on the screen.
public void CombineDataAndDisplay()
{
    // Combine missing data on the calls
   _UserRequests.ToList()
                .ForEach(ur =>
                {
                ur.BillingName     = _Accounts.First(ac => ur.AccountID == ac.AccountID).Name;
                ur.DepartmentName  = _Departments.First(dp => dp.DepartmentID == ur.DepartmentID).Name;
                });


    UserRequests = new PagedCollectionView( _UserRequests);
    UserRequests.GroupDescriptions.Add(new PropertyGroupDescription("DepartmentName"));

}

Multiple Async Methodology Plumbing

Below is what will needed to be brought into your View Model, or placed on your page if not using MVVM. This is where the .Net thread safe Silverlight asynchronous operations will occur.

// Lock Objects 0 for false, 1 for true.
private int AsyncErrorResource = 0;
private int AsyncFinal = 0;

private List<Exception> AsyncErrors;  // If not null errors have been encountered.

private int PendingAsyncOperations; // Holds the counted total of ongoing async operations. Zero means do users final operation.

private Action FinalOperation;      // The user's final operation.

public void MultipleAsyncRun(Action Operation)
{
    Interlocked.Increment(ref PendingAsyncOperations);
    Operation();
}

public void FinalAsync(Action method)
{
    FinalOperation = method;
}

public void AssignResultCheckforAllAsyncsDone<T>(AsyncCompletedEventArgs ea, T receivedData, ref T assignTo, string ErrorMessage)
   where T : class
{
    bool valid = !((ea.Error != null) || (receivedData == null));

    if (valid == false)
    {
        if (0 == Interlocked.Exchange(ref AsyncErrorResource, 1))
        {
            if (AsyncErrors == null)
                AsyncErrors = new List<Exception>();

            AsyncErrors.Add(ea.Error);

            //Release the lock
            Interlocked.Exchange(ref AsyncErrorResource, 0);
        }
    }
    else
    {
        assignTo = receivedData;
    }

    Interlocked.Decrement(ref PendingAsyncOperations);
    if (PendingAsyncOperations == 0)
    {
        if (0 == Interlocked.Exchange(ref AsyncFinal, 1))
        {
            FinalOperation();
        }

        Interlocked.Exchange(ref AsyncFinal, 0);
        Interlocked.Decrement(ref PendingAsyncOperations); // Move to -1
    }
}

That is it, simply use the above code and you can have all your operations work done asynchronously. Now for the disclaimers…

Why Can’t Properties be Used by AssignResultCheckforAllAsyncsDone?

We must use direct variables like in our example

private ObservableCollection<UserRequestDTO> _UserRequests;
private ObservableCollection<Account> _Accounts;
private ObservableCollection<Department> _Deparments;

// Not Private ObservableCollection<Department> _Departments { get; set; }

If one used a property this exception is thrown.

A property, indexer or dynamic member access may not be passed as an out or ref parameter

That is because we are using the generic method AssignResultCheckforAllAsyncsDone to assign a value, and that assignment has to have an exact object instance for the template (T) object and not a Property to assign the value. If your end result is in a property, simply assign it from the variable to the property in the final async call.

Handling Errors

Simply check the error variable if it is not null it has encountered errors.

if (AsyncErrors != null)
{
    MessageBox.Show("Errors: " + string.Join(string.Format("{0}{0}", Environment.NewLine), AsyncErrors.Select(ex => ex.Message)));
}
else
{
    // Success Handle accordingly.
}

Finding Identical Strings using GroupBy

List<string> theList = new List<string>() { "Alpha", "Alpha", "Beta", "Gamma", "Delta" };

theList.GroupBy(txt => txt)
        .Where(grouping => grouping.Count() > 1)
        .ToList()
        .ForEach(groupItem => Console.WriteLine("{0} duplicated {1} times with these values {2}",
                                                 groupItem.Key, 
                                                 groupItem.Count(),
                                                 string.Join(" ", groupItem.ToArray())));
// Writes this out to the console:
//
// Alpha duplicated 2 times with these values Alpha Alpha

Line By Line Explanation

GroupBy Usage with Only Two Defined Keys Regex Example

List<string> theList = new List<string>() { "Alpha", "Alpha", "Beta", "Gamma", "Delta" };

theList.GroupBy( txt => Regex.IsMatch( txt, "ta$" ))
       .ToList()
       .ForEach(groupItem => Console.WriteLine("{0} found {1} times with these values: {2}",
                                                 groupItem.Key,
                                                 groupItem.Count(),
                                                 string.Join(" ", groupItem.ToArray())));
// Output
// False found 3 times with these values: Alpha Alpha Gamma
// True found 2 times with these values: Beta Delta

GroupBy Usage with one Key or a Non Related Key

List<string> theList = new List<string>() { "Alpha", "Alpha", "Beta", "Gamma", "Delta" };

theList.GroupBy(txt => 1 )
        .ToList()
        .ForEach(groupItem => Console.WriteLine("The Key ({0}) found a total of {1} times with a total letter count of {2} characters",
                                                 groupItem.Key,
                                                 groupItem.Count(),
                                                 groupItem.Sum(it => it.Count())));

// Output:
// The Key (1) found a total of 5 times with a total letter count of 24 characters

This snippet is from my archives and reminds me how to setup column names for a WPF/Silverlight datagrid and bind them to the data by not using AutoGenerateColumn feature. (See below for the visual end result.)

Ω Check out the related post Xaml: Adding Visibility Behaviors Using Blend to A DataGrid for WPF or Silverlight

DataGrid Column Names Setup in Xaml

In this example we will have two columns where the data will be filename strings. We will specify the columns in the Xaml to use the DataGridTextColumn and not to dynamically generate columns on our Datagrid:

<DataGrid x:Name="dgOperation" AutoGenerateColumns="False">
    <DataGrid.Columns>
        <DataGridTextColumn Header="File Name Before" Binding="{Binding Path=Original}"/>
        <DataGridTextColumn Header="File Name After"  Binding="{Binding Path=New}"/>
    </DataGrid.Columns>
</DataGrid>

The result is that the header row will have two columns with the name “File Name Before” and “File Name After” will subsequently bind them to a data object with the property names of “Original” and “New”.

Actual Binding During the Loading of the Grid

We will read in a directory for the WPF example from the hard drive and fill the original file names to the first column and a generated name for the second column. Since we have specified in the Xaml that we are binding to “Original” and “New” properties the dynamic linq object created will have those properties.

dgOperation.ItemsSource = Directory.GetFiles( @"C:\" )
                                   .Select( ( nm, index ) => new
                                       {
                                          Original = System.IO.Path.GetFileName( nm ),
                                          New = string.Format( "{0}_{1}{2}", System.IO.Path.GetFileNameWithoutExtension( nm ),
                                                                             index,
                                                                             System.IO.Path.GetExtension( nm ) )
                                        } );

The result is as below:

Note: Out of the box editing the rows will throw an exception. To fix that make each of the rows read only.

(Update 5/16/2011: Fixed mispelling)
I ran across a situation where the code I was working on had an enum with values and I needed to display a user friendly text which was related to the enum but not the enum’s actual text value.

The standard way of mapping values across cultures is to create a localized resource file(s) (.resx) and to put in string key and a string value, where the value will be shown. The code can then do an if check to map between the two; but that gets laborious real quick. It would be better to have a dictionary where the enum is the key and the value is the value of the resources file.

The following snippet of code takes in an enum and its corresponding resource resx data and creates that dictionary. See the section Steps to Test for an example of its usage.

/// <summary>
/// Take an enum and a created corresponding resx resource file and join the two together 
/// into a dictionary. The dictionaries key is the actual enum and the value is the user readable text
/// found in the value of the resource file.
/// </summary>
/// <typeparam name="T">The Enum type which contains the target enums</typeparam>
/// <param name="rm">The .resx resource's manager which contains the mapped text</param>
/// <returns>A dictionary whose key is the enum and the result is the mapped text in the resource file.</returns>
public static Dictionary<T, string> LoadResourceEnumMappings<T>( ResourceManager rm )  
{
    T[] eValues = (T[])System.Enum.GetValues( typeof( T ) ); // Gets the actual values of the enum (T) type

    // Puts those into a local dictionary/hash for use in later.
    var dictEnum = eValues.ToDictionary( it => it.ToString(), it => it ); 

    // Work through the key value pairs (KVP) of the resource set and marry them
    // to a new dictionary where the key is the enum and the value output is the user string
    // as found in the resource's value of its kvp.
    return rm.GetResourceSet( Thread.CurrentThread.CurrentCulture, true, false )
             .OfType<DictionaryEntry>()
             .ToDictionary( kvp => dictEnum[kvp.Key.ToString()], kvp => kvp.Value.ToString() );

}

NOTES

• One can have more resource keys than enums and the above will work. But if there are more enums than resource keys, the above code will throw a KeyNotFound exception.

Enumerate the Embedded Resource

The above code uses the ability to enumerate or iterate the resource file by calling GetResourceSet. That calls returns a Dictionary entry which has the key value pair of the resource file and could be used with a foreach.

Steps To Test

1. Create console application
2. Create enum named MappedValues with these enums : Alpha, Beta, Gamma.

   public enum MappedValues
   {
       Alpha,
       Beta,
       Gamma
   }

3. Create Resource File named UserText.Resx with these values: 

Test as such with this code by calling EnumMapper.Usage():

public static class EnumMapper
{
    /// <summary>
    /// This is just for show and not meant for production.
    /// </summary>
    public static void Usage()
    {
        try
        {
            Console.WriteLine( "Load resource and show: " + UserText.Alpha );

            Dictionary<MappedValues, string> mapped = LoadResourceEnumMappings<MappedValues>( UserText.ResourceManager );

            Console.WriteLine( mapped[MappedValues.Alpha] );

            Console.WriteLine( mapped[MappedValues.Beta] );

            Console.WriteLine( mapped[MappedValues.Gamma] );
        }
        catch ( KeyNotFoundException )
        {
            Console.WriteLine("The Resource File has a key which is not found in the enum.");
        }

/* outputs (Note "first value" was shown to initialize the ResourceManager otherwise it would be null from GetResourceSet)
Load resource and show: First Value
First Value
Second Item
Third Wave
*/
    }

    /// <summary>
    /// Take an enum and a created corresponding resx resource file and join the two together 
    /// into a dictionary. The dictionaries key is the actual enum and the value is the user readable text
    /// found in the value of the resource file.
    /// </summary>
    /// <typeparam name="T">The Enum type which contains the target enums</typeparam>
    /// <param name="rm">The .resx resource's manager which contains the mapped text</param>
    /// <returns>A dictionary whose key is the enum and the result is the mapped text in the resource file.</returns>
    public static Dictionary<T, string> LoadResourceEnumMappings<T>( ResourceManager rm )  
    {
        T[] eValues = (T[])System.Enum.GetValues( typeof( T ) ); // Gets the actual values of the enum (T) type

        // Puts those into a local dictionary/hash for use in later.
        var dictEnum = eValues.ToDictionary( it => it.ToString(), it => it ); 

        // Work through the key value pairs (KVP) of the resource set and marry them
        // to a new dictionary where the key is the enum and the value output is the user string
        // as found in the resource's value of its kvp.
        return rm.GetResourceSet( Thread.CurrentThread.CurrentCulture, true, false )
                    .OfType<DictionaryEntry>()
                    .ToDictionary( kvp => dictEnum[kvp.Key.ToString()], kvp => kvp.Value.ToString() );

    }

}