3rdpartylibs/fastreports.wpf/FastReport/QueryBuilder/FqbCheckedListBox.cs

using System;
using System.Drawing;
using System.Windows.Forms;

namespace FastReport.FastQueryBuilder
{
    internal class FqbCheckedListBox : CheckedListBox
    {
        private Rectangle dragBoxFromMouseDown;

        public event EventHandler VertScrollValueChanged;

        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);
            if (SelectedItem != null)
            {
                Size dragSize = SystemInformation.DragSize;
                dragBoxFromMouseDown = new Rectangle(new Point(e.X - (dragSize.Width / 2),
                                                               e.Y - (dragSize.Height / 2)), dragSize);
            }
            else
                dragBoxFromMouseDown = Rectangle.Empty;
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);
            if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
            {
                if ((dragBoxFromMouseDown != Rectangle.Empty) &&
                    !dragBoxFromMouseDown.Contains(e.X, e.Y))
                {
                    DoDragDrop(SelectedItem, DragDropEffects.Copy);
                }
            }
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            base.OnMouseUp(e);
            dragBoxFromMouseDown = Rectangle.Empty;
        }

#if WPF
        private System.Windows.Controls.ScrollViewer scrollViewer;

        internal Rectangle GetItemRectangle(int pos)
        {
            if (scrollViewer != null)
                pos -= (int)scrollViewer.ContentVerticalOffset;
            return new Rectangle(0, (pos) * ItemHeight, Width, ItemHeight);
        }

        public FqbCheckedListBox()
        {
            control.Loaded += (s, e) =>
            {
                scrollViewer = control.GetChildOfType<System.Windows.Controls.ScrollViewer>();
                scrollViewer.ScrollChanged += (s, e) => VertScrollValueChanged?.Invoke(this, EventArgs.Empty);
            };
        }
#endif

#if AVALONIA
        private Avalonia.Controls.ScrollViewer scrollViewer;

        internal Rectangle GetItemRectangle(int pos)
        {
            int y = pos * ItemHeight;
            if (scrollViewer != null)
                y -= (int)(scrollViewer.Offset.Y / DpiScale);
            return new Rectangle(0, y, Width, ItemHeight);
        }

        public FqbCheckedListBox()
        {
            control.Loaded += (s, e) =>
            {
                scrollViewer = Avalonia.VisualTree.VisualExtensions.FindDescendantOfType<Avalonia.Controls.ScrollViewer>(control);
                scrollViewer.ScrollChanged += (s, e) => VertScrollValueChanged?.Invoke(this, EventArgs.Empty);
            };
        }
#endif

#if !MONO
        private const int WM_VSCROLL = 0x115;

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            if (m.Msg == WM_VSCROLL)
            {
                VertScrollValueChanged?.Invoke(this, EventArgs.Empty);
            }
        }
#endif
    }
}