/V4/PrismLibrary/Desktop/Prism/Regions/Behaviors/SyncRegionContextWithHostBehavior.cs

//===================================================================================

// Microsoft patterns & practices

// Composite Application Guidance for Windows Presentation Foundation and Silverlight

//===================================================================================

// Copyright (c) Microsoft Corporation.  All rights reserved.

// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY

// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT

// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND

// FITNESS FOR A PARTICULAR PURPOSE.

//===================================================================================

// The example companies, organizations, products, domain names,

// e-mail addresses, logos, people, places, and events depicted

// herein are fictitious.  No association with any real company,

// organization, product, domain name, email address, logo, person,

// places, or events is intended or should be inferred.

//===================================================================================

using System;

using System.Windows;

using Microsoft.Practices.Prism.Properties;



namespace Microsoft.Practices.Prism.Regions.Behaviors

{

    /// <summary>

    /// Behavior that synchronizes the <see cref="IRegion.Context"/> property of a <see cref="IRegion"/> with 

    /// the control that hosts the Region. It does this by setting the <see cref="RegionManager.RegionContextProperty"/> 

    /// Dependency Property on the host control.

    /// 

    /// This behavior allows the usage of two way databinding of the RegionContext from XAML. 

    /// </summary>

    public class SyncRegionContextWithHostBehavior : RegionBehavior, IHostAwareRegionBehavior

    {

        private const string RegionContextPropertyName = "Context";

        private DependencyObject hostControl;



        /// <summary>

        /// Name that identifies the SyncRegionContextWithHostBehavior behavior in a collection of RegionsBehaviors. 

        /// </summary>

        public static readonly string BehaviorKey = "SyncRegionContextWithHost";



        private ObservableObject<object> HostControlRegionContext

        {

            get

            {

                return RegionContext.GetObservableContext(this.hostControl);

            }

        }



        /// <summary>

        /// Gets or sets the <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.

        /// </summary>

        /// <value>

        /// A <see cref="DependencyObject"/> that the <see cref="IRegion"/> is attached to.

        /// This is usually a <see cref="FrameworkElement"/> that is part of the tree.

        /// </value>

        public DependencyObject HostControl

        {

            get

            {

                return hostControl;

            }

            set

            {

                if (IsAttached)

                {

                    throw new InvalidOperationException(Resources.HostControlCannotBeSetAfterAttach);

                }

                this.hostControl = value;

            }

        }



        /// <summary>

        /// Override this method to perform the logic after the behavior has been attached.

        /// </summary>

        protected override void OnAttach()

        {

            if (this.HostControl != null)

            {

                // Sync values initially. 

                SynchronizeRegionContext();



                // Now register for events to keep them in sync

                this.HostControlRegionContext.PropertyChanged += this.RegionContextObservableObject_PropertyChanged;

                this.Region.PropertyChanged += this.Region_PropertyChanged;

            }

        }



        void Region_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)

        {

            if (e.PropertyName == RegionContextPropertyName)

            {

                if (RegionManager.GetRegionContext(this.HostControl) != this.Region.Context)

                {

                    // Setting this Dependency Property will automatically also change the HostControlRegionContext.Value

                    // (see RegionManager.OnRegionContextChanged())

                    RegionManager.SetRegionContext(this.hostControl, this.Region.Context);

                }

            }

        }



        void RegionContextObservableObject_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)

        {

            if (e.PropertyName == "Value")

            {

                SynchronizeRegionContext();

            }

        }



        private void SynchronizeRegionContext()

        {

            // Forward this value to the Region

            if (this.Region.Context != this.HostControlRegionContext.Value)

            {

                this.Region.Context = this.HostControlRegionContext.Value;

            }



            // Also make sure the region's DependencyProperty was changed (this can occur if the value

            // was changed only on the HostControlRegionContext)

            if (RegionManager.GetRegionContext(this.HostControl) != this.HostControlRegionContext.Value)

            {

                RegionManager.SetRegionContext(this.HostControl, this.HostControlRegionContext.Value);

            }

        }

    }

}