OnlineMonitorSystem/HandyControl/HandyControl_Shared/Controls/Attach/MenuTopLineAttach.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using HandyControl.Tools;

namespace HandyControl.Controls;

public class MenuTopLineAttach
{
    public static readonly DependencyProperty PopupProperty = DependencyProperty.RegisterAttached(
        "Popup", typeof(Popup), typeof(MenuTopLineAttach), new PropertyMetadata(default(Popup), OnPopupChanged));

    private static void OnPopupChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var topLine = (FrameworkElement) d;

        if (e.NewValue is Popup { TemplatedParent: MenuItem menuItem })
        {
            SetTopLine(menuItem, topLine);
            menuItem.Loaded += MenuItem_Loaded;
        }
    }

    private static void MenuItem_Loaded(object sender, RoutedEventArgs e)
    {
        var menuItem = (FrameworkElement) sender;
        menuItem.Unloaded += MenuItem_Unloaded;
        var topLine = GetTopLine(menuItem);
        var popup = GetPopup(topLine);
        if (popup != null)
        {
            popup.Opened += Popup_Opened;
        }
    }

    private static void MenuItem_Unloaded(object sender, RoutedEventArgs e)
    {
        var menuItem = (FrameworkElement) sender;
        menuItem.Unloaded -= MenuItem_Unloaded;
        var topLine = GetTopLine(menuItem);
        var popup = GetPopup(topLine);
        if (popup != null)
        {
            popup.Opened -= Popup_Opened;
        }
    }

    private static void Popup_Opened(object sender, EventArgs e)
    {
        var popup = (Popup) sender;
        if (popup.TemplatedParent is MenuItem menuItem)
        {
            var topLine = GetTopLine(menuItem);
            if (topLine == null) return;

            topLine.HorizontalAlignment = HorizontalAlignment.Left;
            topLine.Width = menuItem.ActualWidth;
            topLine.Margin = new Thickness();

            var positionLeftTop = menuItem.PointToScreen(new Point());
            var positionRightBottom = menuItem.PointToScreen(new Point(menuItem.ActualWidth, menuItem.ActualHeight));
            ScreenHelper.FindMonitorRectsFromPoint(positionLeftTop, out _, out var workAreaRect);
            var panel = VisualHelper.GetParent<Panel>(topLine);

            if (positionLeftTop.X < 0)
            {
                topLine.Margin = new Thickness(positionLeftTop.X - panel.Margin.Left, 0, 0, 0);
            }
            else if (positionLeftTop.X + panel.ActualWidth > workAreaRect.Right)
            {
                var overflowWidth = positionRightBottom.X - workAreaRect.Right;
                if (overflowWidth > 0)
                {
                    topLine.Width -= overflowWidth + panel.Margin.Right;
                }
                topLine.HorizontalAlignment = HorizontalAlignment.Left;
                topLine.Margin = new Thickness(positionLeftTop.X + panel.ActualWidth - workAreaRect.Right + panel.Margin.Right, 0, 0, 0);
            }

            if (positionRightBottom.Y > workAreaRect.Bottom)
            {
                topLine.Width = 0;
                topLine.HorizontalAlignment = HorizontalAlignment.Stretch;
                topLine.Margin = new Thickness();
            }
        }
    }

    public static void SetPopup(DependencyObject element, Popup value)
        => element.SetValue(PopupProperty, value);

    public static Popup GetPopup(DependencyObject element)
        => (Popup) element.GetValue(PopupProperty);

    internal static readonly DependencyProperty TopLineProperty = DependencyProperty.RegisterAttached(
        "TopLine", typeof(FrameworkElement), typeof(MenuTopLineAttach), new PropertyMetadata(default(FrameworkElement)));

    internal static void SetTopLine(DependencyObject element, FrameworkElement value)
        => element.SetValue(TopLineProperty, value);

    internal static FrameworkElement GetTopLine(DependencyObject element)
        => (FrameworkElement) element.GetValue(TopLineProperty);
}