C# MemoryCache學習筆記_ZenDei技術網路在線

很多情況下需要用到緩存，合理利用緩存一方面可以提高程式的響應速度，同時可以減少對特定資源訪問的壓力。為了避免每次請求都去訪問後臺的資源（例如資料庫），一般會考慮將一些更新不是很頻繁的、可以重用的數據，通過一定的方式臨時地保存起來，後續的請求根據情況可以直接訪問這些保存起來的數據，這種機制就是所謂 ...

很多情況下需要用到緩存，合理利用緩存一方面可以提高程式的響應速度，同時可以減少對特定資源訪問的壓力。為了避免每次請求都去訪問後臺的

資源（例如資料庫），一般會考慮將一些更新不是很頻繁的、可以重用的數據，通過一定的方式臨時地保存起來，後續的請求根據情況可以直接訪問這

些保存起來的數據，這種機制就是所謂的緩存機制。

.NET 4.0的緩存功能主要由三部分組成：System.Runtime.Caching，System.Web.Caching.Cache和Output Cache。

MemoryCache：這個是在.NET 4.0中新增的緩存框架，Namespace:System.Runtime.Caching ，Assembly:System.Runtime.Caching.dll。

System.Web.Caching.Cache：這個是在.NET 2.0開始就一直存在的緩存對象，一般主要用在Web中，當然也可以用於Winform裡面，不過要引用

System.Web.dll。

Output Cache：這個是在Asp.NET裡面使用的。在ASP.NET 4.0之前，都是直接使用System.Web.Caching.Cache來緩存HTML片段。在ASP.NET 4.0

中對它進行了重新設計，提供了一個OutputCacheProvider供開發人員進行擴展，但是它預設情況下，仍然使用System.Web.Caching.Cache來做做緩存。

下麵演示MemoryCache的簡單使用：

1、添加一個類，命名為ConfigHelper，代碼如下：

    /// <summary>
    /// 配置幫助類
    /// </summary>
    class ConfigHelper
    {
        /// <summary>
        /// 獲取管理配置文件對象
        /// </summary>
        /// <param name="configPath">指定要管理的配置文件路徑，如果為空或不存在，則為管理程式集預設的配置文件路徑。</param>
        /// <returns></returns>
        private static Configuration GetConfiguration(string configPath = null)
        {
            if (!string.IsNullOrEmpty(configPath) && File.Exists(configPath))
            {
                ExeConfigurationFileMap map = new ExeConfigurationFileMap
                {
                    ExeConfigFilename = configPath
                };
                return ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);
            }
            else
            {
                return ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            }
        }

        /// <summary>
        /// 獲取指定配置文件+配置名稱的配置項的值
        /// </summary>
        public static string GetAppSettingValue(string key, string defaultValue = null, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            var appSetting = config.AppSettings.Settings[key];
            return appSetting.Value;
        }

        /// <summary>
        /// 獲取所有配置值
        /// </summary>
        public static Dictionary<string, string> GetAppSettingValues(string configPath = null)
        {
            Dictionary<string, string> settingDic = new Dictionary<string, string>();
            var config = GetConfiguration(configPath);
            var settings = config.AppSettings.Settings;
            foreach (string key in settings.AllKeys)
            {
                settingDic[key] = settings[key].ToString();
            }
            return settingDic;
        }

        /// <summary>
        /// 設置配置值（存在則更新，不存在則新增。）
        /// </summary>
        public static void SetAppSettingValue(string key, string value, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            var setting = config.AppSettings.Settings[key];
            if (setting == null)
            {
                config.AppSettings.Settings.Add(key, value);
            }
            else
            {
                setting.Value = value;
            }

            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("appSettings");
        }

        /// <summary>
        /// 設置多個配置值（存在則更新，不存在則新增）
        /// </summary>
        public static void SetAppSettingValues(IEnumerable<KeyValuePair<string, string>> settingValues, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            foreach (var item in settingValues)
            {
                var setting = config.AppSettings.Settings[item.Key];
                if (setting == null)
                {
                    config.AppSettings.Settings.Add(item.Key, item.Value);
                }
                else
                {
                    setting.Value = item.Value;
                }
            }
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("appSettings");
        }

        /// <summary>
        /// 刪除配置值
        /// </summary>
        public static void RemoveAppSetting(string key, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            config.AppSettings.Settings.Remove(key);
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("appSettings");
        }

        /// <summary>
        /// 刪除多個配置值
        /// </summary>
        public static void RemoveAppSettings(string configPath = null, params string[] keys)
        {
            var config = GetConfiguration(configPath);
            if (keys != null)
            {
                foreach (string key in keys)
                {
                    config.AppSettings.Settings.Remove(key);
                }
            }
            else
            {
                config.AppSettings.Settings.Clear();
            }
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("appSettings");
        }

        /// <summary>
        /// 獲取連接字元串
        /// </summary>
        public static string GetConnectionString(string name, string defaultconnString = null, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            var connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
            if (connStringSettings == null)
            {
                return defaultconnString;
            }
            return connStringSettings.ConnectionString;
        }

        /// <summary>
        /// 獲取指定配置文件+連接名稱的連接字元串配置項
        /// </summary>
        public static ConnectionStringSettings GetConnectionStringSetting(string name, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            var connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
            return connStringSettings;
        }

        /// <summary>
        /// 獲取所有的連接字元串配置項
        /// </summary>
        public static Dictionary<string, ConnectionStringSettings> GetConnectionStringSettings(string configPath = null)
        {
            var config = GetConfiguration(configPath);
            var connStringSettingDic = new Dictionary<string, ConnectionStringSettings>();
            var connStringSettings = ConfigurationManager.ConnectionStrings;
            foreach (ConnectionStringSettings item in connStringSettings)
            {
                connStringSettingDic[item.Name] = item;
            }
            return connStringSettingDic;
        }

        /// <summary>
        /// 設置連接字元串的值（存在則更新，不存在則新增。）
        /// </summary>
        public static void SetConnectionString(string name, string connString, string provider, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            ConnectionStringSettings connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
            if (connStringSettings != null)
            {
                connStringSettings.ConnectionString = connString;
                connStringSettings.ProviderName = provider;
            }
            else
            {
                connStringSettings = new ConnectionStringSettings(name, connString, provider);
                config.ConnectionStrings.ConnectionStrings.Add(connStringSettings);
            }

            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("connectionStrings");
        }

        /// <summary>
        /// 設置多個連接字元串的值（存在則更新，不存在則新增。）
        /// </summary>
        public static void SetConnectionStrings(IEnumerable<ConnectionStringSettings> connStringSettings, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            foreach (var item in connStringSettings)
            {
                ConnectionStringSettings connStringSetting = config.ConnectionStrings.ConnectionStrings[item.Name];
                if (connStringSetting != null)
                {
                    connStringSetting.ConnectionString = item.ConnectionString;
                    connStringSetting.ProviderName = item.ProviderName;
                }
                else
                {
                    config.ConnectionStrings.ConnectionStrings.Add(item);
                }
            }

            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("connectionStrings");
        }

        /// <summary>
        /// 刪除連接字元串配置項
        /// </summary>
        public static void RemoveConnectionString(string name, string configPath = null)
        {
            var config = GetConfiguration(configPath);
            config.ConnectionStrings.ConnectionStrings.Remove(name);
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("connectionStrings");
        }

        /// <summary>
        /// 刪除多個連接字元串配置項
        /// </summary>
        public static void RemoveConnectionStrings(string configPath = null, params string[] names)
        {
            var config = GetConfiguration(configPath);
            if (names != null)
            {
                foreach (string name in names)
                {
                    config.ConnectionStrings.ConnectionStrings.Remove(name);
                }
            }
            else
            {
                config.ConnectionStrings.ConnectionStrings.Clear();
            }
            config.Save(ConfigurationSaveMode.Modified);
            ConfigurationManager.RefreshSection("connectionStrings");
        }
    }

View Code

2、添加一個類，命名為MemoryCacheHelper（註意需引用System.Runtime.Caching.dll），代碼如下：

    /// <summary>
    /// 記憶體緩存幫助類，支持絕對過期時間、滑動過期時間、文件依賴三種緩存方式。
    /// </summary>
    class MemoryCacheHelper
    {
        private static readonly object _locker1 = new object(), _locker2 = new object();

        /// <summary>
        /// 取緩存項，如果不存在則返回空。
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static T GetCacheItem<T>(string key)
        {
            try
            {
                return (T)MemoryCache.Default[key];
            }
            catch
            {
                return default(T);
            }
        }

        /// <summary>
        /// 是否包含指定鍵的緩存項
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static bool Contains(string key)
        {
            return MemoryCache.Default.Contains(key);
        }

        /// <summary>
        /// 取緩存項，如果不存在則新增緩存項。
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <param name="cachePopulate"></param>
        /// <param name="slidingExpiration"></param>
        /// <param name="absoluteExpiration"></param>
        /// <returns></returns>
        public static T GetOrAddCacheItem<T>(string key, Func<T> cachePopulate, TimeSpan? slidingExpiration = null, DateTime? absoluteExpiration = null)
        {
            if (string.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");
            if (cachePopulate == null) throw new ArgumentNullException("cachePopulate");
            if (slidingExpiration == null && absoluteExpiration == null) throw new ArgumentException("Either a sliding expiration or absolute must be provided");

            if (MemoryCache.Default[key] == null)
            {
                lock (_locker1)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && cacheValue == null)   //如果是引用類型且為NULL則不存緩存
                        {
                            return cacheValue;
                        }

                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(slidingExpiration, absoluteExpiration);

                        MemoryCache.Default.Add(item, policy);
                    }
                }
            }

            return (T)MemoryCache.Default[key];
        }

        /// <summary>
        /// 取緩存項，如果不存在則新增緩存項。
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <param name="cachePopulate"></param>
        /// <param name="dependencyFilePath"></param>
        /// <returns></returns>
        public static T GetOrAddCacheItem<T>(string key, Func<T> cachePopulate, string dependencyFilePath)
        {
            if (string.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");
            if (cachePopulate == null) throw new ArgumentNullException("cachePopulate");

            if (MemoryCache.Default[key] == null)
            {
                lock (_locker2)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && cacheValue == null)   //如果是引用類型且為NULL則不存緩存
                        {
                            return cacheValue;
                        }

                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(dependencyFilePath);

                        MemoryCache.Default.Add(item, policy);
                    }
                }
            }

            return (T)MemoryCache.Default[key];
        }

        /// <summary>
        /// 指定緩存項的一組逐出和過期詳細信息
        /// </summary>
        /// <param name="slidingExpiration"></param>
        /// <param name="absoluteExpiration"></param>
        /// <returns></returns>
        private static CacheItemPolicy CreatePolicy(TimeSpan? slidingExpiration, DateTime? absoluteExpiration)
        {
            var policy = new CacheItemPolicy();

            if (absoluteExpiration.HasValue)
            {
                policy.AbsoluteExpiration = absoluteExpiration.Value;
            }
            else if (slidingExpiration.HasValue)
            {
                policy.SlidingExpiration = slidingExpiration.Value;
            }

            policy.Priority = CacheItemPriority.Default;

            return policy;
        }

        /// <summary>
        /// 指定緩存項的一組逐出和過期詳細信息
        /// </summary>
        /// <param name="filePath"></param>
        /// <returns></returns>
        private static CacheItemPolicy CreatePolicy(string filePath)
        {
            CacheItemPolicy policy = new CacheItemPolicy();
            policy.ChangeMonitors.Add(new HostFileChangeMonitor(new List<string>() { filePath }));
            policy.Priority = CacheItemPriority.Default;
            return policy;
        }

        /// <summary>
        /// 移除指定鍵的緩存項
        /// </summary>
        /// <param name="key"></param>
        public static void RemoveCacheItem(string key)
        {
            if (Contains(key))
            {
                MemoryCache.Default.Remove(key);
            }
        }
    }

View Code

3、添加一個WinForm窗體，命名為Main，並添加一個按鈕。

4、配置App.config：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <startup> 
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
  </startup>
  <connectionStrings>
    <add name ="connString" connectionString="server=.;database=db_test;uid=sa;pwd=********;" />
  </connectionStrings>
</configuration>

5、Main窗體代碼如下：

        private void button1_Click(object sender, EventArgs e)
        {
            int times1 = 0, times2 = 0;
            for (int i = 0; i < 10; i++)
            {
                if (MemoryCacheHelper.Contains("connString"))
                {
                    times1++;
                }
                else
                {
                    times2++;
                    string connstr = MemoryCacheHelper.GetOrAddCacheItem("connString", () =>
                    {
                        return ConfigHelper.GetConnectionString("connString", null);
                    }, Application.StartupPath + @"\App.config");
                }
            }
            MessageBox.Show($"記憶體緩存讀取次數：{times1}，非記憶體緩存讀取次數：{times2}", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }

6、運行結果如下：

參考自：

https://www.cnblogs.com/mq0036/p/10312945.html

https://www.cnblogs.com/zuowj/p/8366735.html

https://www.cnblogs.com/zuowj/p/8440902.html