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In addition to handling events, it is important to commit to your developer audience. Because of this, you also must decide which functionality and properties you will allow other developers to access. In the case of the rating control, providing a hook into the rating that the user selected seems beneficial. Because of this, provide a rating property that other developers can use to access the control:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace CustomControlLibrary
{
   /// <summary>
   /// Interaction logic for RatingUserControl.xaml
   /// </summary>
   public partial class RatingUserControl :
      System.Windows.Controls.UserControl
   {
      public RatingUserControl()
      {
         InitializeComponent();
      }

      // The selected rating within the control
      private int rating = 0;

      /// <summary>
      /// The selected rating within the control
      /// </summary>
      public int Rating
      {
         get { return rating; }
         set { rating = value;}
      }

      /// <summary>
      /// Handles the user clicking a rating element (an ellipse)
      /// </summary>
      public void OnMouseLeftButtonUp(object sender, RoutedEventArgs e)
      {
         // The last value of the name of the object represents the rating
         string selectedEllipseName = ((Ellipse)(e.Source)).Name;
         string selectedRating =
            selectedEllipseName.Substring(selectedEllipseName.Length-1);

         // Convert the rating to an int
         rating = Convert.ToInt32(selectedRating);
      }

      /// <summary>
      /// Handles the user entering the boundaries of a rating
      /// element (an ellipse)
      /// </summary>
      public void OnMouseEnter(object sender, RoutedEventArgs e)
      {
         // Store the name of the ellipse that the user is over and
         /// create a flag.
         string selectedEllipseName = ((Ellipse)(e.Source)).Name;
         bool found = false;

         // Iterate through the child ellipses and set the rating
         // based on the currently selected ellipse. It is assumed
         // that the children will always be ellipses.
         foreach (UIElement child in EllipsesStackPanel.Children)
         {
            // Set the style of the ellipse accordingly
            if (found == true)
               ellipse.Style = (Style)(this.Resources["UnselectedStyle"]);
            else
               ellipse.Style = (Style)(this.Resources["SelectedStyle"]);

            // Determine if this is the ellipse the user is currently
            // hovering over.
            if (ellipse.Name == selectedEllipseName)
               found = true;
         }
      }

      /// <summary>
      /// Handles the user leaving the boundaries of a rating
      /// element (an ellipse)
      /// </summary>
      public void OnMouseLeave(object sender, RoutedEventArgs e)
      {
         // Determine which entry you want to stop at
         string previousRating = "Ellipse" + rating;
         bool found = false;

         // Iterate through the child ellipses and set the rating
         // based on the currently selected ellipse. It is assumed
         // that the children will always be ellipses.
         foreach (UIElement child in EllipsesStackPanel.Children)
         {
            // Set the style of the ellipse accordingly
            Ellipse ellipse = (Ellipse)(child);
            if ((found == true) || (rating == 0))
               ellipse.Style = (Style)(this.Resources["UnselectedStyle"]);
            else
               ellipse.Style = (Style)(this.Resources["SelectedStyle"]);

            // Determine if you have found what you were looking for
            if (ellipse.Name == previousRating)
               found = true;
         }
      }
   }
}

Much like user controls from previous .NET UI components, you have the ability to implement a code-behind class; this enables you to separate the procedural code from the user experience implementation. The custom class derives from System.Windows.Controls.UserControl. The rest of the implementation will be familiar to .NET developers. This familiarity makes WPF development great!

Testing

To test the custom control, you need to create a wrapper application. The purpose of the wrapper application is to test the complete control conclusively, including the following:

• User experience: XAMLPad is a great tool for testing the layout and appearance of controls. However, it lacks the ability to test user interaction because the event handling is implemented within the code-behind.
• Data binding: It is possible that through the programmatic handles (the methods and properties) another developer may render the control differently based on data from a data source. For instance, you may want to display the rating the user previously entered.

The Custom Controls of Your Dreams

The source code for this practical example provides the framework for developing the custom controls of your dreams, and in the case of the example, the rating control of your dreams. With the combination of the powerful user experience provided by WPF and the productivity of reusing custom controls, it has become easier than ever to fulfill your end users' application desires.

Acknowledgement

This article was edited by Rachel Wireman.

About the Author

Chad Campbell (MCSD, MCTS) is a solutions developer for mid- to large-sized organizations. He is a thought leader with Crowe Chizek in Indianapolis, Indiana. Chad specializes in Web-based solutions, Reach him at cacampbell@crowechizek.com.

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