wpftoolkit/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/Magnifier/Implementation/MagnifierManager.cs

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

namespace Microsoft.Windows.Controls
{
    public class MagnifierManager : DependencyObject
    {
        #region Members

        private MagnifierAdorner _adorner;
        private UIElement _element;

        #endregion //Members

        #region Properties

        public static readonly DependencyProperty CurrentProperty = DependencyProperty.RegisterAttached("Magnifier", typeof(Magnifier), typeof(UIElement), new FrameworkPropertyMetadata(null, OnMagnifierChanged));
        public static void SetMagnifier(UIElement element, Magnifier value)
        {
            element.SetValue(CurrentProperty, value);
        }
        public static Magnifier GetMagnifier(UIElement element)
        {
            return (Magnifier)element.GetValue(CurrentProperty);
        }

        private static void OnMagnifierChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            UIElement target = d as UIElement;

            if (target == null)
                throw new ArgumentException("Magnifier can only be attached to a UIElement.");

            MagnifierManager manager = new MagnifierManager();
            manager.AttachToMagnifier(target, e.NewValue as Magnifier);
        }

        #endregion //Properties

        #region Event Handlers

        void Element_MouseLeave(object sender, MouseEventArgs e)
        {
            HideAdorner();
        }

        void Element_MouseEnter(object sender, MouseEventArgs e)
        {
            ShowAdorner();
        }

        #endregion //Event Handlers

        #region Methods

        private void AttachToMagnifier(UIElement element, Magnifier magnifier)
        {
            _element = element;
            _element.MouseEnter += Element_MouseEnter;
            _element.MouseLeave += Element_MouseLeave;

            magnifier.Target = _element;

            _adorner = new MagnifierAdorner(_element, magnifier);
        }

        void ShowAdorner()
        {
            VerifyAdornerLayer();
            _adorner.Visibility = Visibility.Visible;
        }

        bool VerifyAdornerLayer()
        {
            if (_adorner.Parent != null)
                return true;

            AdornerLayer layer = AdornerLayer.GetAdornerLayer(_element);
            if (layer == null)
                return false;

            layer.Add(_adorner);
            return true;
        }

        void HideAdorner()
        {
            if (_adorner.Visibility == Visibility.Visible)
            {
                _adorner.Visibility = Visibility.Collapsed;
            }
        }

        #endregion //Methods
    }
}