/V4/PrismLibrary/Desktop/Prism.MefExtensions/Modularity/MefFileModuleTypeLoader.Desktop.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.ComponentModel.Composition;

using System.ComponentModel.Composition.Hosting;

using System.IO;

using Microsoft.Practices.Prism.Modularity;



namespace Microsoft.Practices.Prism.MefExtensions.Modularity

{

    /// <summary>

    /// Loads modules from an arbitrary location on the filesystem. This typeloader is only called if 

    /// <see cref="ModuleInfo"/> classes have a Ref parameter that starts with "file://". 

    /// This class is only used on the Desktop version of the Composite Application Library when used with Managed Extensibility Framework.

    /// </summary>  

    [Export]

    public class MefFileModuleTypeLoader : IModuleTypeLoader

    {

        private const string RefFilePrefix = "file://";

        private readonly HashSet<Uri> downloadedUris = new HashSet<Uri>();



        // disable the warning that the field is never assigned to, and will always have its default value null

        // as it is imported by MEF

#pragma warning disable 0649

        [Import(AllowRecomposition = false)]

        private AggregateCatalog aggregateCatalog;

#pragma warning restore 0649



        /// <summary>

        /// Initializes a new instance of the MefFileModuleTypeLoader class.

        /// This instance is used to load requested module types.

        /// </summary>

        public MefFileModuleTypeLoader()

        {

        }



        #region IModuleTypeLoader Members



        /// <summary>

        /// Raised repeatedly to provide progress as modules are loaded in the background.

        /// </summary>

        public virtual event EventHandler<ModuleDownloadProgressChangedEventArgs> ModuleDownloadProgressChanged;



        /// <summary>

        /// Raised when a module is loaded or fails to load.

        /// </summary>

        public virtual event EventHandler<LoadModuleCompletedEventArgs> LoadModuleCompleted;



        /// <summary>

        /// Evaluates the <see cref="ModuleInfo.Ref"/> property to see if the current typeloader will be able to retrieve the <paramref name="moduleInfo"/>.

        /// Returns true if the <see cref="ModuleInfo.Ref"/> property starts with "file://", because this indicates that the file

        /// is a local file. 

        /// </summary>

        /// <param name="moduleInfo">Module that should have it's type loaded.</param>

        /// <returns>

        ///     <see langword="true"/> if the current typeloader is able to retrieve the module, otherwise <see langword="false"/>.

        /// </returns>

        public virtual bool CanLoadModuleType(ModuleInfo moduleInfo)

        {

            if (moduleInfo == null)

            {

                throw new System.ArgumentNullException("moduleInfo");

            }



            return moduleInfo.Ref != null && moduleInfo.Ref.StartsWith(RefFilePrefix, StringComparison.Ordinal);

        }



        /// <summary>

        /// Retrieves the <paramref name="moduleInfo"/>.

        /// </summary>

        /// <param name="moduleInfo">Module that should have it's type loaded.</param>

        public virtual void LoadModuleType(ModuleInfo moduleInfo)

        {

            if (moduleInfo == null)

            {

                throw new System.ArgumentNullException("moduleInfo");

            }



            try

            {

                Uri uri = new Uri(moduleInfo.Ref, UriKind.RelativeOrAbsolute);



                // If this module has already been downloaded, I fire the completed event.

                if (this.IsSuccessfullyDownloaded(uri))

                {

                    this.RaiseLoadModuleCompleted(moduleInfo, null);

                }

                else

                {

                    string path = moduleInfo.Ref.Substring(RefFilePrefix.Length + 1);



                    long fileSize = -1L;

                    if (File.Exists(path))

                    {

                        FileInfo fileInfo = new FileInfo(path);

                        fileSize = fileInfo.Length;

                    }



                    // Although this isn't asynchronous, nor expected to take very long, I raise progress changed for consistency.

                    this.RaiseModuleDownloadProgressChanged(moduleInfo, 0, fileSize);



                    this.aggregateCatalog.Catalogs.Add(new AssemblyCatalog(path));



                    // Although this isn't asynchronous, nor expected to take very long, I raise progress changed for consistency.

                    this.RaiseModuleDownloadProgressChanged(moduleInfo, fileSize, fileSize);



                    // I remember the downloaded URI.

                    this.RecordDownloadSuccess(uri);



                    this.RaiseLoadModuleCompleted(moduleInfo, null);

                }

            }

            catch (Exception ex)

            {

                this.RaiseLoadModuleCompleted(moduleInfo, ex);

            }

        }



        #endregion



        private void RaiseModuleDownloadProgressChanged(

            ModuleInfo moduleInfo,

            long bytesReceived,

            long totalBytesToReceive)

        {

            this.RaiseModuleDownloadProgressChanged(new ModuleDownloadProgressChangedEventArgs(

                                                        moduleInfo, bytesReceived, totalBytesToReceive));

        }



        private void RaiseModuleDownloadProgressChanged(ModuleDownloadProgressChangedEventArgs e)

        {

            if (this.ModuleDownloadProgressChanged != null)

            {

                this.ModuleDownloadProgressChanged(this, e);

            }

        }



        private void RaiseLoadModuleCompleted(ModuleInfo moduleInfo, Exception error)

        {

            this.RaiseLoadModuleCompleted(new LoadModuleCompletedEventArgs(moduleInfo, error));

        }



        private void RaiseLoadModuleCompleted(LoadModuleCompletedEventArgs e)

        {

            if (this.LoadModuleCompleted != null)

            {

                this.LoadModuleCompleted(this, e);

            }

        }



        private bool IsSuccessfullyDownloaded(Uri uri)

        {

            lock (this.downloadedUris)

            {

                return this.downloadedUris.Contains(uri);

            }

        }



        private void RecordDownloadSuccess(Uri uri)

        {

            lock (this.downloadedUris)

            {

                this.downloadedUris.Add(uri);

            }

        }

    }

}