/V4/MVVM RI/MVVM.Client/Infrastructure/StateManagement/StateHandler.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.ComponentModel.Composition.Hosting;



namespace MVVM.Client.Infrastructure.StateManagement

{

    /// <summary>

    /// Provides access to state management objects in the container and handles setting state while returning previous values.

    /// </summary>

    public class StateHandler

    {

        private readonly CompositionContainer container;



        public StateHandler(CompositionContainer container)

        {

            this.container = container;

        }



        public T SetState<T>(T context)

        {

            return SetCurrentState<T>(context);

        }



        /// <summary>

        /// Sets <paramref name="context"/> as the current context for type <typeparamref name="T"/>.

        /// </summary>

        private T SetCurrentState<T>(T context)

        {

            var currentState = GetInstance<ICurrentState<T>>();

            var previousValue = currentState.Value;

            currentState.Value = context;



            return previousValue;

        }



        private T GetInstance<T>()

        {

            return this.container.GetExportedValue<T>();

        }

    }

}