Display_D_HP/TeamAAS-VM/Behaviors/DatePickerUserSelectionBehavior.cs

using Microsoft.Xaml.Behaviors;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace TeamAAS_VP.Behaviors
{
    public class DatePickerUserSelectionBehavior : Behavior<DatePicker>
    {
        public static readonly DependencyProperty UserSelectionCommandProperty =
            DependencyProperty.Register(
                nameof(UserSelectionCommand),
                typeof(ICommand),
                typeof(DatePickerUserSelectionBehavior));

        public ICommand UserSelectionCommand
        {
            get => (ICommand)GetValue(UserSelectionCommandProperty);
            set => SetValue(UserSelectionCommandProperty, value);
        }

        public static readonly DependencyProperty CommandParameterProperty =
            DependencyProperty.Register(
                nameof(CommandParameter),
                typeof(object),
                typeof(DatePickerUserSelectionBehavior));

        public object CommandParameter
        {
            get => GetValue(CommandParameterProperty);
            set => SetValue(CommandParameterProperty, value);
        }

        private bool _isUserInteraction = false;
        private DateTime? _previousDate;

        protected override void OnAttached()
        {
            base.OnAttached();
            AssociatedObject.PreviewMouseDown += OnPreviewMouseDown;
            AssociatedObject.CalendarOpened += OnCalendarOpened;
            AssociatedObject.SelectedDateChanged += OnSelectedDateChanged;
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            AssociatedObject.PreviewMouseDown -= OnPreviewMouseDown;
            AssociatedObject.CalendarOpened -= OnCalendarOpened;
            AssociatedObject.SelectedDateChanged -= OnSelectedDateChanged;
        }

        private void OnPreviewMouseDown(object sender, MouseButtonEventArgs e)
        {
            _isUserInteraction = true;
            _previousDate = AssociatedObject.SelectedDate;
        }

        private void OnCalendarOpened(object sender, RoutedEventArgs e)
        {
            _isUserInteraction = true;
            _previousDate = AssociatedObject.SelectedDate;
        }

        private void OnSelectedDateChanged(object sender, SelectionChangedEventArgs e)
        {
            if (_isUserInteraction && UserSelectionCommand?.CanExecute(CommandParameter) == true)
            {
                var parameter = new Tuple<object, DateTime?, DateTime?>(
                    CommandParameter,
                    _previousDate,
                    AssociatedObject.SelectedDate);

                UserSelectionCommand.Execute(parameter);
            }
            _isUserInteraction = false;
        }
    }
}