WPF DataGrid Custom Column Sorting

With thanks to Aran Holland with this Stackoverflow answer.
I wanted to sort a DataGrid by StudentID. Unfortunately the StudentID is mainly numeric but with an alpha prefix - typically S12345. Paul had previously written SortableStringValue so I just needed to hook that up to the DataGrid using a custom class that implements IComparer.
In the code-behind I hooked up the DataGrid's Sorting event in the constructor.

public StudentCourseSearchView()
{
   InitializeComponent();

   SearchResults.Sorting += new DataGridSortingEventHandler(SearchResults_Sorting);
}

Then in the private SearchResults_Sorting method I determine if it is the StudentID column that is being sorted and instantiate the custom sorting class.

void SearchResults_Sorting(object sender, System.Windows.Controls.DataGridSortingEventArgs e)
{
   DataGridColumn column = e.Column;

   // I'm only interested in a custom sort for the StudentID column
   if (column.SortMemberPath != "StudentID.Number") return;

   IComparer comparer = null;

   // Prevent the built-in sort from sorting 
   e.Handled = true;

   ListSortDirection direction = (column.SortDirection != ListSortDirection.Ascending) ? ListSortDirection.Ascending : ListSortDirection.Descending;

   // Set the sort order on the column 
   column.SortDirection = direction;

   //use a ListCollectionView to do the sort. 
   ListCollectionView lcv = (ListCollectionView)CollectionViewSource.GetDefaultView(TypedViewModel.Students);

   // Instantiate the custom sort class which implements IComparer
   comparer = new StudentSearchResultStudentIdSort(direction);

   // Apply the sort 
   lcv.CustomSort = comparer;
}

Finally, the StudentSearchResultStudentIdSort class implements the Compare method using the SortableStringValue extension method.

public class StudentSearchResultStudentIdSort : IComparer
{
   ListSortDirection _direction;

   public StudentSearchResultStudentIdSort(ListSortDirection direction)
   {
      _direction = direction;
   }
   public int Compare(object x, object y)
   {
      string studentIdX = (x as StudentSearchResult).StudentID.Value;
      string studentIdY = (y as StudentSearchResult).StudentID.Value;

      if (_direction == ListSortDirection.Ascending)
      {
         return studentIdX.SortableStringValue().CompareTo(studentIdY.SortableStringValue());
      }
      else
      {
         return studentIdY.SortableStringValue().CompareTo(studentIdX.SortableStringValue());
      }
   }
}

Simple WPF ColorPicker ComboBox

I needed a ColorPicker that could be embedded in a DataGrid, simple to operate and could save the color name in the database. A ComboBox seemed the obvious choice.
A simple list of colors is reasonably straightforward using a little Reflection:

      public List<string> SimpleColorList
      {
         get
         {
            List<string> colorList = new List<string>();
            foreach (PropertyInfo pi in typeof(Colors).GetProperties())
            {
               colorList.Add(pi.Name);
            }
            return colorList;
         }
      }

And bound it to a ComboBox. Using Mode=OneTime means the ColorList is only built once.

<ComboBox ItemsSource="{Binding Path=SimpleColorList, Mode=OneTime}"
            SelectedValue="{Binding SelectedColor}"
            Width="200" />

Adding a ItemTemplate to the ComboBox makes it a little more interesting:

<ComboBox ItemsSource="{Binding Path=SimpleColorList, Mode=OneTime}"
            SelectedValue="{Binding SelectedColor}"
            Width="200">
   <ComboBox.ItemTemplate>
      <DataTemplate>
         <StackPanel Orientation="Horizontal">
            <TextBlock Width="130"
                        Text="{Binding}" />
            <Border BorderBrush="Black"
                     BorderThickness="1"
                     CornerRadius="4"
                     Margin="0,1,0,1"
                     Background="{Binding}"
                     Width="40"
                     Height="18">
            </Border>
         </StackPanel>
      </DataTemplate>
   </ComboBox.ItemTemplate>
</ComboBox>

The straight alphabetic sorted list is fine but I wanted to sort by "color", in general terms from lighter to darker. I found some code on the web that would convert the RGB into the HSL color space. (I'm afraid I can't find the code again so my apologies to its author for the lack of attribution).

   public static class HslValueConverter
   {
      /// <summary>
      /// Converts a WPF RGB color to an HSL color
      /// </summary>
      /// <param name="rgbColor">The RGB color to convert.</param>
      /// <returns>An HSL color object equivalent to the RGB color object passed in.</returns>
      public static HslColor RgbToHsl(string name, Color rgbColor)
      {
         // Initialize result
         var hslColor = new HslColor();
         hslColor.Name = name;

         // Convert RGB values to percentages
         double r = (double)rgbColor.R / 255;
         var g = (double)rgbColor.G / 255;
         var b = (double)rgbColor.B / 255;
         var a = (double)rgbColor.A / 255;

         // Find min and max RGB values
         var min = Math.Min(r, Math.Min(g, b));
         var max = Math.Max(r, Math.Max(g, b));
         var delta = max - min;

         /* If max and min are equal, that means we are dealing with 
          * a shade of gray. So we set H and S to zero, and L to either
          * max or min (it doesn't matter which), and  then we exit. */

         //Special case: Gray
         if (max == min)
         {
            hslColor.Hue = 0;
            hslColor.Saturation = 0;
            hslColor.Lightness = max;
            return hslColor;
         }

         /* If we get to this point, we know we don't have a shade of gray. */

         // Set L
         hslColor.Lightness = (min   max) / 2;

         // Set S
         if (hslColor.Lightness < 0.5)
         {
            hslColor.Saturation = delta / (max   min);
         }
         else
         {
            hslColor.Saturation = delta / (2.0 - max - min);
         }

         // Set H
         if (r == max) hslColor.Hue = (g - b) / delta;
         if (g == max) hslColor.Hue = 2.0   (b - r) / delta;
         if (b == max) hslColor.Hue = 4.0   (r - g) / delta;
         hslColor.Hue *= 60;
         if (hslColor.Hue < 0) hslColor.Hue  = 360;

         // Set A
         hslColor.Alpha = a;

         // Set return value
         return hslColor;

      }
   }
   public struct HslColor
   {
      public string Name { get; set; }
      public double Alpha;
      public double Hue;
      public double Lightness;
      public double Saturation;
   }

Then I changed the property (Note: the property name has changed to SortedColorList, so the ComboBox Binding will have to be altered) "getter" to sort by Saturation, Hue and Lightness. I also decided to exclude the Transparent color.

      public List<string> SortedColourList
      {
         get
         {
            List<HslColor> colorList = new List<HslColor>();
            foreach (PropertyInfo pi in typeof(Colors).GetProperties())
            {
               Color color = (Color)pi.GetValue(null, null);
               // Only select non-Transparent colors
               if (color.A != 0) colorList.Add(HslValueConverter.RgbToHsl(pi.Name, color));
            }
            return colorList.OrderBy(c => c.Saturation)
                         .OrderBy(c => c.Hue)
                         .OrderByDescending(c => c.Lightness)
                         .Select(c => c.Name).ToList<string>();
         }
      }

The SimpleColorPicker project is available on GoogleCode.

SortableStringValue

We have a number of different alphanumeric codes in our application that occasionally need to be sorted. Using the standard sorting mechanism we typically end up with a list that looks like this:
A1
A10
A2
A20
A3
A4

Paul has written an extension method that allows us to sort into alpha then numeric order, like this:
A1
A2
A3
A4
A10
A20

The extension method is used like this:
    var result = list.OrderBy(l => l.SortableStringValue())

public static class Extensions
{
   public static String SortableStringValue(this String text)
   {
      StringBuilder  textBuilder;
      StringBuilder  numberBuilder;
      textBuilder = new StringBuilder();
      numberBuilder = new StringBuilder();
      //Look at each char in the string
      foreach(char value in text)
      {
         switch (value)
         {
            //If its a number add it to the number builder
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
               numberBuilder.Append(value);
               break;
            //Else add it to the text builder
            default:             
               //Before we add the text, format and add any number we may have
               if (numberBuilder.Length > 0)
               {
                  textBuilder.Append(numberBuilder.ToString().PadLeft(16,'0'));
                  numberBuilder.Clear();
               }
               textBuilder.Append(value);
                  
               break;
         }
      }

      //Check to see if we have any numbers left in the builder
      if (numberBuilder.Length > 0)
      {
         textBuilder.Append(numberBuilder.ToString().PadLeft(16,'0'));
      }
      //Return the string value (The replace will allow negative number to be sorted)
      return textBuilder.ToString().Replace("-0","-00");
   }
}

Sorting Arrays

Martin pointed me at this interesting blog regarding Array.Sort Sorting Arrays

I used Array.Sort previously in this post Sorting and De-Duping Arrays but didn't investigate further at that time.

A quick look at Array.Sort(...) shows that it has 17 overloads and lots of things to try out at some point in the future.

Sorting and De-duping arrays

I seem to be obsessed with sorting based on the number of posts I've made on the topic.
Sorting a simple string[] is easy using:

string[] recordIds = { "q", "z", "a", "b", "q" };

Array.Sort(recordIds);

To stop a third party component from failing we had to ensure that our string[] array contained only unique strings. Sorting and de-duping using LINQ could be done in a single line:

string[] recordIds = { "q", "z", "a", "b", "q" };

var sortedUniqueIds = (from id in recordIds orderby id select id).Distinct();

int i=0;

foreach (string id in sortedUniqueIds)

{

   recordIds[i++] = id;

}

Microsoft have an excellent LINQ samples page: 101 LINQ Samples

Sorting Generic Collections - Redux

Using LINQ it turns out to be quite easy to sort a generic Dictionary by either Key or Value.

In these examples a list of sorted keys is returned in the 'keys' variable.

Alternately the LINQ statement can used directly in a foreach loop.

Dictionary<string, string> dict = new Dictionary<string, string>();
...

// Sort by Key
var keys = from key in dict.Keys orderby key ascending select key;

// Sort by Value
var keys = from key in dict.Keys orderby dict[key] ascending select key;

// Sort within foreach(...) by Key
foreach(string aKey in (from key in dict.Keys orderby key ascending select key)){
  ...
}

Sorting a collection using Linq and 'SortExpression' string

Bruce suggested that we use LINQ to sort collections. I found the following code on Miron Abrahason's blog but haven't had the chance to try it out yet.

Already happened to you that you had a collection of object from type 'X' with some properties, and you had to sort it one time by property 'ID', and another time by property 'Name' ? You wished that you can sort it by just using a 'Sort Expression' ? If still not, I'm sure this moment will arrive sooner or later. Let me save you some time and an headache.

This is how it can be done:

public static IEnumerable Sort(this IEnumerable source, string sortExpression)
{
    string[] sortParts = sortExpression.Split(' ');
    var param = Expression.Parameter(typeof(T), string.Empty);
    try
    {
        var property = Expression.Property(param, sortParts[0]);
        var sortLambda = Expression.Lambda>(Expression.Convert(property,         typeof(object)), param);
        if (sortParts.Length > 1 && sortParts[1].Equals("desc", StringComparison.OrdinalIgnoreCase))
        {
            return source.AsQueryable().OrderByDescending(sortLambda);
        }
        return source.AsQueryable().OrderBy(sortLambda);
    }
    catch (ArgumentException)
    {
        return source;
    }
}

Just drop it in a static class, and you will be able to sort any collection that implement the interface IEnumerable.

Lets say you have a class 'User':

public class User
{
    public int ID { get; set; }
    public string Name { get; set; }
}

and a List collection: users. You can sort it however you want:

IEnumerable sortedUsersIEnumerable = users.Sort("ID desc");

Or

List sortedUsersList = users.Sort("Name").ToList();

Sorting Generic Collections

You can simplify the sorting by using the anonymous delegate as shown below and you don't need to implement IComparable interface:

(Note: For a simpler technique using LINQ see: Sorting Generic Collections - Redux)

List persons = new List();
persons.Add( new Person("Tom",30) );
persons.Add(new Person("Harry", 55));

// sort in ascending order
persons.Sort( delegate(Person person0, Person person1)
{
return
person0.FirstName.CompareTo(person1.FirstName);
} );


// sort in descending order
persons.Sort( delegate(Person person0, Person person1)
{
return
person1.FirstName.CompareTo(person0.FirstName);
} );