Interaction.cs

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using Dreamine.MVVM.Behaviors.Core.Interfaces;
using System;
using System.Windows;
 
namespace Dreamine.MVVM.Behaviors.Wpf.Interactivity
{
    public static class Interaction
    {
        public static readonly DependencyProperty BehaviorsProperty =
            DependencyProperty.RegisterAttached(
                "Behaviors",
                typeof(BehaviorCollection),
                typeof(Interaction),
                new FrameworkPropertyMetadata(null, OnBehaviorsChanged));

        public static BehaviorCollection GetBehaviors(DependencyObject obj)
        {
            ArgumentNullException.ThrowIfNull(obj);
 
            BehaviorCollection? collection =
                (BehaviorCollection?)obj.GetValue(BehaviorsProperty);
 
            if (collection is not null)
            {
                return collection;
            }
 
            collection = new BehaviorCollection();
            obj.SetValue(BehaviorsProperty, collection);
 
            return collection;
        }

        public static void SetBehaviors(DependencyObject obj, BehaviorCollection? value)
        {
            ArgumentNullException.ThrowIfNull(obj);
            obj.SetValue(BehaviorsProperty, value);
        }

        private static void OnBehaviorsChanged(
            DependencyObject obj,
            DependencyPropertyChangedEventArgs args)
        {
            BehaviorCollection? oldCollection = (BehaviorCollection?)args.OldValue;
            BehaviorCollection? newCollection = (BehaviorCollection?)args.NewValue;
 
            if (ReferenceEquals(oldCollection, newCollection))
            {
                return;
            }
 
            if (oldCollection is not null &&
                ((IAttachedObject)oldCollection).AssociatedObject is not null)
            {
                oldCollection.Detach();
            }
 
            if (newCollection is not null)
            {
                newCollection.Attach(obj);
            }
        }
    }
}