Prism6下的MEF：基于微软企业库的Cache

通常，应用程序可以将那些频繁访问的数据，以及那些需要大量处理时间来创建的数据存储在内存中，从而提高性能。基于微软的企业库，我们的快速创建一个缓存的实现。

新建PrismSample.Infrastructure.Cache

新建一个类库项目，将其命名为PrismSample.Infrastructure.Cache，然后从nuget中下载微软企业库的Cache。

然后新建我们的CacheManager类：

using Microsoft.Practices.EnterpriseLibrary.Caching;
using System.ComponentModel.Composition;

namespace PrismSample.Infrastructure.Cache
{
    [Export("PrismSampleCache", typeof(ICacheManager))]
    public class CacheManager : ICacheManager
    {
        ICacheManager _cacheManager;

        public CacheManager()
        {
            _cacheManager = CacheFactory.GetCacheManager("MemoryCacheManager");
        }

        public object this[string key]
        {
            get
            {
                return _cacheManager[key];
            }
        }

        public int Count
        {
            get
            {
                return _cacheManager.Count;
            }
        }

        public void Add(string key, object value)
        {
            _cacheManager.Add(key, value);
        }

        public void Add(string key, object value, CacheItemPriority scavengingPriority, ICacheItemRefreshAction refreshAction, params ICacheItemExpiration[] expirations)
        {
            _cacheManager.Add(key, value, scavengingPriority, refreshAction, expirations);
        }

        public bool Contains(string key)
        {
            return _cacheManager.Contains(key);
        }

        public void Flush()
        {
            _cacheManager.Flush();
        }

        public object GetData(string key)
        {
        return  _cacheManager.GetData(key);
        }

        public void Remove(string key)
        {
            _cacheManager.Remove(key);
        }
    }
}

其中MemoryCacheManager是我们稍后需要在App.config文件中配置的。

修改生成后事件：

xcopy "$(TargetPath)" "$(SolutionDir)\PrismSample\bin\Debug\" /Y

之所以添加生成后事件，是因为Cache的类库的引入不是通过Project间的项目引用来实现的，是在运行时MEF的容器去寻找指令集，所以我们把程序集都放置到运行目录下。

修改App.config配置文件

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
        <section name="cachingConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Caching.Configuration.CacheManagerSettings, Microsoft.Practices.EnterpriseLibrary.Caching" />
    </configSections>
        <startup> 
            <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
        </startup>
    <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <dependentAssembly>
            <assemblyIdentity name="Microsoft.Practices.ServiceLocation" publicKeyToken="31bf3856ad364e35" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-1.3.0.0" newVersion="1.3.0.0" />
        </dependentAssembly>
        </assemblyBinding>
    </runtime>
    <cachingConfiguration defaultCacheManager="MemoryCacheManager">
        <cacheManagers>
        <add name="MemoryCacheManager" type="Microsoft.Practices.EnterpriseLibrary.Caching.CacheManager, Microsoft.Practices.EnterpriseLibrary.Caching" expirationPollFrequencyInSeconds="60" maximumElementsInCacheBeforeScavenging="1000" numberToRemoveWhenScavenging="10" backingStoreName="NullBackingStore" />
        </cacheManagers>
        <backingStores>
        <add type="Microsoft.Practices.EnterpriseLibrary.Caching.BackingStoreImplementations.NullBackingStore, Microsoft.Practices.EnterpriseLibrary.Caching"
            name="NullBackingStore" />
        </backingStores>
    </cachingConfiguration>
</configuration>

配置文件的生成可以通过微软企业库的工具(配置方式)

修改Bootstrapper，将目录下符合条件的dll全部导入

using Prism.Mef;
using PrismSample.Infrastructure.Abstract.Presentation.Interface;
using System.ComponentModel.Composition.Hosting;
using System.Windows;
using Prism.Logging;
using PrismSample.Infrastructure.Logger;
using System.IO;
using System;

namespace PrismSample
{
    public class Bootstrapper : MefBootstrapper
    {
        private const string SEARCH_PATTERN = "PrismSample.Infrastructure.*.dll";

        protected override DependencyObject CreateShell()
        {
            IViewModel shellViewModel = this.Container.GetExportedValue<IViewModel>("ShellViewModel");      
            return shellViewModel.View as DependencyObject;
        }

        protected override void InitializeShell()
        {
            Application.Current.MainWindow = (Shell)this.Shell;
            Application.Current.MainWindow.Show();
        }

        protected override void ConfigureAggregateCatalog()
        {
            base.ConfigureAggregateCatalog();

            //加载自己
            this.AggregateCatalog.Catalogs.Add(new AssemblyCatalog(this.GetType().Assembly));

            //加载当前目录
            DirectoryInfo dirInfo = new DirectoryInfo(@".\");
            foreach (FileInfo fileInfo in dirInfo.EnumerateFiles(SEARCH_PATTERN))
            {
                try
                {
                    this.AggregateCatalog.Catalogs.Add(new AssemblyCatalog(fileInfo.FullName));
                }
                catch (Exception ex)
                {
                    this.Logger.Log( string.Format("导入异常：{0}", ex.Message), Category.Exception, Priority.None);
                }
            }
        }

        protected override ILoggerFacade CreateLogger()
        {
            return new Logger();
        }
    }
}

测试运行

修改ShellViewModel的构造函数

[ImportingConstructor]
public ShellViewModel([Import("ShellView", typeof(IView))]IView view, 
                        [Import]ILoggerFacade logger, 
                        [Import("PrismSampleCache", typeof(ICacheManager))] ICacheManager _cacheManager)
{
    this.View = view;
    this.View.DataContext = this;

    _cacheManager.Add("SampleValue", "CacheValue");
    this._text = _cacheManager.GetData("SampleValue").ToString();
    logger.Log("ShellViewModel Created", Category.Info, Priority.None);
}

运行结果：

小结

本文用微软企业库实现了一个简单的缓存系统。
源码下载

参考信息

patterns & practices – Enterprise Library
黄聪：Microsoft Enterprise Library 5.0 系列教程(一) : Caching Application Block (初级)