TreeView滚动TreeViewItem

 今天帮忙修了一个bug， 在拖动TreeViewItem时，需要滚动TreeView向前翻页，或向后翻页。

思路：

1.找到TreeView控件里的ItemsControl

2.找到ItemsControl里的ScrollViewer

3.判断当前每个Item的高度

4.通过GetCursorPos获取屏幕绝对坐标

5.通过ItemsControl的PointFromScreen把屏幕坐标转为相对于ItemsControl的客户坐标

6.判断当前坐标是否超出第一Item或者最后一个Item

7.如果超出第一个Item则向上滚动， 如果超出最后一个Item则向下滚动。

       [StructLayout(LayoutKind.Sequential)]
        public struct POINT
        {
            public int X;
            public int Y;
 
            public POINT(int x, int y)
            {
                this.X = x;
                this.Y = y;
            }
 
            public override string ToString()
            {
                return ("X:" + X + ", Y:" + Y);
            }
        }
 
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern bool GetCursorPos(out POINT pt);

private void ScrollItemToView(object sender)
        {
            ItemsControl itemsControl = sender as ItemsControl;
            if (null == itemsControl)
            {
                return;
            }
 
            if (null == this.targetItemContainer)
            {
                return;
            }
 
            ScrollViewer scv = Utilities.FindChild<ScrollViewer>(itemsControl);
            if (null != scv)
            {
               //每个Item的Container的高度
                double itemHeight = this.targetItemContainer.ActualHeight;
 
                POINT currentPosition = new POINT();
                GetCursorPos(out currentPosition);
 
                Point relativePos = itemsControl.PointFromScreen(new Point(currentPosition.X, currentPosition.Y));
 
                if (relativePos.Y >= itemsControl.ActualHeight - itemHeight)
                {
                    scv.ScrollToVerticalOffset(scv.VerticalOffset + itemHeight);
                }
                else if (relativePos.Y <= itemHeight)
                {
                    scv.ScrollToVerticalOffset(scv.VerticalOffset - itemHeight);
                }
            }
        }