/V4/PrismLibrary/Desktop/Prism/Regions/RegionNavigationContentLoader.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.Collections.Generic;

using System.Globalization;

using System.Linq;

using System.Windows;

using Microsoft.Practices.Prism.Properties;

using Microsoft.Practices.ServiceLocation;



namespace Microsoft.Practices.Prism.Regions

{

    /// <summary>

    /// Implementation of <see cref="IRegionNavigationContentLoader"/> that relies on a <see cref="IServiceLocator"/>

    /// to create new views when necessary.

    /// </summary>

    public class RegionNavigationContentLoader : IRegionNavigationContentLoader

    {

        private readonly IServiceLocator serviceLocator;



        /// <summary>

        /// Initializes a new instance of the <see cref="RegionNavigationContentLoader"/> class with a service locator.

        /// </summary>

        /// <param name="serviceLocator">The service locator.</param>

        public RegionNavigationContentLoader(IServiceLocator serviceLocator)

        {

            this.serviceLocator = serviceLocator;

        }



        /// <summary>

        /// Gets the view to which the navigation request represented by <paramref name="navigationContext"/> applies.

        /// </summary>

        /// <param name="region">The region.</param>

        /// <param name="navigationContext">The context representing the navigation request.</param>

        /// <returns>

        /// The view to be the target of the navigation request.

        /// </returns>

        /// <remarks>

        /// If none of the views in the region can be the target of the navigation request, a new view

        /// is created and added to the region.

        /// </remarks>

        /// <exception cref="ArgumentException">when a new view cannot be created for the navigation request.</exception>

        public object LoadContent(IRegion region, NavigationContext navigationContext)

        {

            if (region == null) throw new ArgumentNullException("region");

            if (navigationContext == null) throw new ArgumentNullException("navigationContext");



            string candidateTargetContract = this.GetContractFromNavigationContext(navigationContext);



            var candidates = this.GetCandidatesFromRegion(region, candidateTargetContract);



            var acceptingCandidates =

                candidates.Where(

                    v =>

                    {

                        var navigationAware = v as INavigationAware;

                        if (navigationAware != null && !navigationAware.IsNavigationTarget(navigationContext))

                        {

                            return false;

                        }



                        var frameworkElement = v as FrameworkElement;

                        if (frameworkElement == null)

                        {

                            return true;

                        }



                        navigationAware = frameworkElement.DataContext as INavigationAware;

                        return navigationAware == null || navigationAware.IsNavigationTarget(navigationContext);

                    });





            var view = acceptingCandidates.FirstOrDefault();



            if (view != null)

            {

                return view;

            }



            view = this.CreateNewRegionItem(candidateTargetContract);



            region.Add(view);



            return view;

        }



        /// <summary>

        /// Provides a new item for the region based on the supplied candidate target contract name.

        /// </summary>

        /// <param name="candidateTargetContract">The target contract to build.</param>

        /// <returns>An instance of an item to put into the <see cref="IRegion"/>.</returns>

        protected virtual object CreateNewRegionItem(string candidateTargetContract)

        {

            object newRegionItem;

            try

            {           

                newRegionItem = this.serviceLocator.GetInstance<object>(candidateTargetContract);

            }

            catch (ActivationException e)

            {

                throw new InvalidOperationException(

                    string.Format(CultureInfo.CurrentCulture, Resources.CannotCreateNavigationTarget, candidateTargetContract),

                    e);

            }

            return newRegionItem;

        }



        /// <summary>

        /// Returns the candidate TargetContract based on the <see cref="NavigationContext"/>.

        /// </summary>

        /// <param name="navigationContext">The navigation contract.</param>

        /// <returns>The candidate contract to seek within the <see cref="IRegion"/> and to use, if not found, when resolving from the container.</returns>

        protected virtual string GetContractFromNavigationContext(NavigationContext navigationContext)

        {

            if (navigationContext == null) throw new ArgumentNullException("navigationContext");



            var candidateTargetContract = UriParsingHelper.GetAbsolutePath(navigationContext.Uri);

            candidateTargetContract = candidateTargetContract.TrimStart('/');

            return candidateTargetContract;

        }



        /// <summary>

        /// Returns the set of candidates that may satisfiy this navigation request.

        /// </summary>

        /// <param name="region">The region containing items that may satisfy the navigation request.</param>

        /// <param name="candidateNavigationContract">The candidate navigation target as determined by <see cref="GetContractFromNavigationContext"/></param>

        /// <returns>An enumerable of candidate objects from the <see cref="IRegion"/></returns>

        protected virtual IEnumerable<object> GetCandidatesFromRegion(IRegion region, string candidateNavigationContract)

        {

            if (region == null) throw new ArgumentNullException("region");

            return region.Views.Where(v =>

                string.Equals(v.GetType().Name, candidateNavigationContract, StringComparison.Ordinal) ||

                string.Equals(v.GetType().FullName, candidateNavigationContract, StringComparison.Ordinal));

        }

    }

}