The simplest way to detect DoubleClick in Silverlight

by Jim McCurdy 7. August 2009 22:32

Here is a simple static class, MouseButtonHelper, that offers a single method, IsDoubleClick, to determine if a standard MouseLeftButtonDown or MouseLeftButtonUp event is a double click. In the past I have used timers, and Triggers and Behaviors to accomplish the same thing, but this approach is less code, less XAML, and uses a lot less resources.

Usage is as follows:

In XAML or in code behind, handle the standard MouseLeftButtonDown or MouseLeftButtonUp event for the object you wish to perform double click handling.
Implement the handler function for the above event as follows:

public void OnMouseButtonDown(object sender, MouseButtonEventArgs e)
{
	bool doubleClick = MouseButtonHelper.EventIsDoubleClick(sender, e);
	if (doubleClick)
		MessageBox.Show("Double click detected!", "Alert", MessageBoxButton.OK);
}

The code below has been tested and used with Silverlight 3 and Silverlight 4.

using System;
using System.Windows;
using System.Windows.Input;

namespace ClassLibrary
{
	internal static class MouseButtonHelper
	{
		private const long k_DoubleClickSpeed = 500;
		private const double k_MaxMoveDistance = 20;

		private static long m_LastClickTicks = 0;
		private static Point m_LastPosition;
		private static object m_LastSender;

		internal static bool IsDoubleClick(object sender, MouseButtonEventArgs e)
		{
			bool senderMatch = sender.Equals(m_LastSender);
			m_LastSender = sender;

			long clickTicks = DateTime.Now.Ticks;
			Point position = e.GetPosition(null);
			if (senderMatch)
			{
				long elapsedTicks = clickTicks - m_LastClickTicks;
				long elapsedTime = elapsedTicks / TimeSpan.TicksPerMillisecond;
				double distance = position.Distance(m_LastPosition);
				if (elapsedTime <= k_DoubleClickSpeed && distance <= k_MaxMoveDistance)
				{
					// Double click!
					m_LastClickTicks = 0;
					return true;
				}
			}

			// Not a double click
			m_LastClickTicks = clickTicks;
			m_LastPosition = position;
			return false;
		}

		private static double Distance(this Point pointA, Point pointB)
		{
			double x = pointA.X - pointB.X;
			double y = pointA.Y - pointB.Y;
			return Math.Sqrt(x * x + y * y);
		}
	}
}