aistudio-wpf-diagram/gong-wpf-dragdrop/src/GongSolutions.WPF.DragDrop/DragAdorner.cs

using System.Windows.Documents;
using System.Windows;
using System.Windows.Media;

namespace GongSolutions.Wpf.DragDrop
{
    internal class DragAdorner : Adorner
    {
        public DragAdorner(UIElement adornedElement, UIElement adornment, Point translation, DragDropEffects effects = DragDropEffects.None)
            : base(adornedElement)
        {
            this._translation = translation;
            this.m_AdornerLayer = AdornerLayer.GetAdornerLayer(adornedElement);
            this.m_AdornerLayer.Add(this);
            this.m_Adornment = adornment;
            this.IsHitTestVisible = false;
            this.Effects = effects;
        }

        public DragDropEffects Effects { get; private set; }

        public Point MousePosition
        {
            get { return this.m_MousePosition; }
            set
            {
                if (this.m_MousePosition != value)
                {
                    this.m_MousePosition = value;
                    this.m_AdornerLayer.Update(this.AdornedElement);
                }
            }
        }

        public void Detatch()
        {
            this.m_AdornerLayer.Remove(this);
        }

        protected override Size ArrangeOverride(Size finalSize)
        {
            this.m_Adornment.Arrange(new Rect(finalSize));
            return finalSize;
        }

        public override GeneralTransform GetDesiredTransform(GeneralTransform transform)
        {
            var result = new GeneralTransformGroup();
            result.Children.Add(base.GetDesiredTransform(transform));
            result.Children.Add(new TranslateTransform(this.MousePosition.X + this._translation.X, this.MousePosition.Y + this._translation.Y));

            return result;
        }

        protected override Visual GetVisualChild(int index)
        {
            return this.m_Adornment;
        }

        protected override Size MeasureOverride(Size constraint)
        {
            this.m_Adornment.Measure(constraint);
            return this.m_Adornment.DesiredSize;
        }

        protected override int VisualChildrenCount
        {
            get { return 1; }
        }

        private readonly AdornerLayer m_AdornerLayer;
        private readonly UIElement m_Adornment;
        private Point m_MousePosition;
        private Point _translation;
    }
}