Future/Future.Contract/Adorners/DragDropAdorner.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Media;

namespace Future.Contract
{
    /// <summary>
    /// 拖动辅助装饰器
    /// </summary>
    public class DragDropAdorner : Adorner
    {
        #region   静态变量区
        private static DragDropAdorner sAdorner;            //装饰器：拖放过程中所有效果绘制使用的装饰器对象，结束后会释放
        private static AdornerLayer sLayer;                 //装饰层：用于放置拖放效果装饰器，拖放过程结束后会清除对象引用

        private static UIElement sOrigin;                   //拖起目标：被拖动的源对象
        private static UIElement sTarget;                   //放置目标：在拖动过程中用于放置拖动源的目标，随拖动过程而变化

        private static Canvas sCanvas;                      //拖放画布：整个拖放过程的完整区域，是拖起目标与放置目标的祖辈
        private static Border sShadow;                      //鼠标拖起阴影：用于将托起目标尺寸按照相同缩放比缩放后变成阴影
        private static Canvas sEffect;                      //鼠标拖动效果：用于提示放置的参考点位置，左、上、右、下，中。

        private static Dock sPosition;                      //参考放置位置：为放置目标的位置提供参考，左、上、右、下，中。

        /// <summary>
        /// 放置的参考点
        /// </summary>
        public static Dock DropPosition { get => sPosition; }
        #endregion
        #region   静态方法区
        /// <summary>
        /// 设定完整拖放效果区域以及被拖动的对象，或是等效对象来起动拖放事件
        /// </summary>
        /// <param name="area">完整的拖放区域，必须是拖起目标与放置目标的共同祖先节点</param>
        /// <param name="origin">被拖动的可视化目标，或是其等效目标</param>
        /// <returns></returns>
        public static DragDropEffects DoDragDrop(UIElement area, UIElement dragSource, object data, DragDropEffects allowedEffects)
        {
            DragDropEffects dragDropEffects = allowedEffects;
            //TODO：准备拖放，生成阴影，监听拖动执行区域中的拖动事件
            dragDropEffects = DragDrop.DoDragDrop(dragSource, data, dragDropEffects);
            //TODO：拖拽操作完成，释放装饰器以及过程中使用的所有资源
            sLayer.Remove(sAdorner);
            return dragDropEffects;
        }

        private static void OnDragEnter(UIElement target, DragEventArgs args)
        {
            sTarget= target;
            target.MouseMove += Target_MouseMove;
            //TODO：更换目标对象，监听目标对象的鼠标事件，规制“阴影”与“效果”
        }

        private static void Target_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {
            //TODO：计算鼠标位置，移动效果与阴影
        }
        //public static void OnDragOver(UIElement target, DragEventArgs args)
        //{
        //    //TODO：计算鼠标位置，移动效果与阴影
        //}
        public static void OnDragLeave(UIElement target, DragEventArgs args)
        { 
            //TODO：清除目标对象，清除对鼠标事件的监听，清除“阴影”与“效果”
            target.MouseMove -= Target_MouseMove;
        }
        public static void DropCompleted(UIElement target, DragEventArgs args)
        {
            //TODO：清除静态存储区中所使用过的数据，清除装饰器
        }
        #endregion
        private readonly VisualCollection mVisuals;
        private DragDropAdorner(UIElement adornedElement) : base(adornedElement)
        {
            mVisuals = new VisualCollection(this);
            sCanvas = new Canvas
            {
                Background=Brushes.Transparent
            };
            
            mVisuals.Add(sCanvas);
            sLayer = AdornerLayer.GetAdornerLayer(adornedElement);
            sLayer?.Add(this);
        }

        protected override int VisualChildrenCount => mVisuals.Count;

        protected override Visual GetVisualChild(int index) => mVisuals[index];

        protected override Size ArrangeOverride(Size finalSize)
        {
            //var bubbleSize = _bubble.DesiredSize;
            //var location = new Point(finalSize.Width + 10, (finalSize.Height - bubbleSize.Height) / 2);
            //_bubble.Arrange(new Rect(location, DesiredSize));
            sCanvas.Arrange(new Rect(new Point(), finalSize));
            return finalSize;
        }
    }
}