LoadAwareRegionBehavior raise ViewLoaded/ViewUnloaded methods when View.Loaded/View.Unloaded events raise.

ILoadAware.cs

using System;

namespace Microsoft.Practices.Prism.Regions
{
    /// <summary>
    /// Represent ILoadAware functionality for View-Model classes.
    /// </summary>
    public interface ILoadAware
    {
        /// <summary>
        /// Gets called by RegionManager when associated View.Loaded event raise.
        /// </summary>
        void ViewLoaded();

        /// <summary>
        /// Gets called by RegionManager when associated View.Unloaded event raise.
        /// </summary>
        void ViewUnloaded();
    }
}

LoadAwareRegionBehavior.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;

namespace Microsoft.Practices.Prism.Regions
{
    public class LoadAwareRegionBehavior : RegionBehavior
    {
        public const string BehaviorKey = "LoadAwareRegion";

        protected override void OnAttach()
        {
            this.Region.Views.CollectionChanged += RegionActiveViewsChanged;
        }

        private void RegionActiveViewsChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (e.Action == NotifyCollectionChangedAction.Remove)
            {
                UnregisterEventHandlers(e.OldItems);
            }
            else if (e.Action == NotifyCollectionChangedAction.Add)
            {
                RegisterEventHandlers(e.NewItems);
            }
        }

        private static void RegisterEventHandlers(IList views)
        {
            foreach (var view in views)
            {
                var frameworkElement = view as FrameworkElement;
                if (frameworkElement != null)
                {
                    var loadAwareDataContext = frameworkElement.DataContext as ILoadAware;
                    if (loadAwareDataContext != null)
                    {
                        frameworkElement.Loaded += (s, e) => loadAwareDataContext.ViewLoaded();
                        frameworkElement.Unloaded += (s, e) => loadAwareDataContext.ViewUnloaded();
                    }
                }
            }
        }

        private static void UnregisterEventHandlers(IList views)
        {
            foreach (var view in views)
            {
                var frameworkElement = view as FrameworkElement;
                if (frameworkElement != null)
                {
                    var loadAwareDataContext = frameworkElement.DataContext as ILoadAware;
                    if (loadAwareDataContext != null)
                    {
                        frameworkElement.Loaded -= (s, e) => loadAwareDataContext.ViewLoaded();
                        frameworkElement.Unloaded -= (s, e) => loadAwareDataContext.ViewUnloaded();
                    }
                }
            }
        }
    }
}