[.NET] Rough Dependency Injection

动机

在设计系统架构的时候，在系统里加入Dependency Injection(DI)，让系统可以在不改变程序代码的状况下，抽换类别来提高重用性、扩充性。在.NET里可以选择一些的Framework来使用，例如：Spring Framework、Unity Application Block、Managed Extensibility Framework (MEF)。

在一些中小型项目，套用上列这些Framework，常常会有种拿大炮打蚊子的感觉。因为这些Framework为了能够符合更多的使用情景，而加入了很多功能。一直加下去的结果，就是系统变的庞大并且较难理解上手。以Spring来说，光是怎么写配置文件的操作，都可以写成书了。当然这样用意是好的，一个够强大的Framework学习曲线必然会较高，但是学会之后能适用的范围也会更广。

不过不得面对的现实是，很多开发人员没时间学习各种Framework(或是无心学习?)。在系统架构里加入这些强大Framework，提高了系统的各项质量时，也拉高技术门坎。过高的技术门坎在后续开发、维护，补充人手时会越来越艰难…。以此为发想于是就萌生了：建立简单易用的一组类别，完成Dependency Injection(DI)应该具备的基础功能。只需要学习基础功能，就能为系统加入Dependency Injection(DI)功能。这样就能降低开发人员的技术门坎，让更多的开发人员能做为补充人力加入项目。

本篇文章介绍一个实作Dependency Injection(DI)基础功能的Rough Dependency Injection实作，这个实作定义对象之间的职责跟互动，用来反射生成要注入的对象。为自己做个纪录，也希望能帮助到有需要的开发人员。

* 必须要特别声明的是，Spring、MEF这些Framework有很高的价值。当这些Framework成为整个团队基础开发知识时，整个团队的开发能力将会提升一个台阶。

结构

Rough Dependency Injection主要是将Dependency Injection(DI) 基础功能，拆为两大部分：对象生成、对象设定，并且将复杂的对象设定隔离在系统之外。模式的结构如下：

主要的参与者有：

TEntity
-欲注入系统的对象。

IReflectProfileRepository
- ReflectProfile进出系统边界的接口。
-将对象设定隔离在系统之外，可以抽换各种不同数据存储。
-极端的案例可以抽换成为HardCodeRepository，连设定都从系统移除。

ReflectProfile
-DTO物件。
-储存用来反射生成IReflectBuilder所需要的参数。

IReflectBuilder
-经由ReflectProfile储存参数，反射生成的对象接口。
-使用ReflectProfile储存参数，生成TEntity。

ReflectManager
-藉由IReflectProfileRepository取得系统储存的ReflectProfile。
-使用ReflectProfile储存参数，反射生成IReflectBuilder。
-使用IReflectBuilder与ReflectProfile，生成TEntity。

透过下面的图片说明，可以了解相关对象之间的互动流程。

实作

范列下载

实作说明请参照范例程序内容：RoughDependencyInjectionSample点此下载

ReflectProfile、IReflectProfileRepository

首先为了将对象设定这个职责，隔离在系统之外。所以在整个模块的边界套用Repository模式，建立出IReflectProfileRepository。并且使用ReflectProfile做为进出系统边界的DTO对象，这个ReflectProfile对象储存生成对象的参数数据。

namespace CLK.Reflection
{
    public sealed class ReflectProfile
    {
        // Constructors
        public ReflectProfile()
        {
            // Default
            this.ProfileName = string.Empty;
            this.BuilderType = string.Empty;
            this.Parameters = new Dictionary<string, string>();
        }


        // Properties
        public string ProfileName { get; set; }

        public string BuilderType { get; set; }

        public Dictionary<string, string> Parameters { get; private set; }
    }
}

namespace CLK.Reflection
{
    public interface IReflectProfileRepository
    {
        // Methods
        string GetDefaultProfileName(string reflectSpace);

        ReflectProfile GetProfile(string reflectSpace, string profileName);

        IEnumerable<ReflectProfile> CreateAllProfile(string reflectSpace);
    }
}

IReflectBuilder、ReflectManager

接着处理ReflectManager来使用ReflectProfile。ReflectManager主要的工作就是透过IReflectProfileRepository取得的ReflectProfile，用ReflectProfile来反射生成IReflectBuilder实作。然后在利用这个IReflectBuilder实作，配合ReflectProfile来生成系统需要注入的TEntity。之所以不直接反射生成TEntity另外再建一层IReflectBuilder，是因为不希望在TEntity里，混入DI相关功能的相依。

namespace CLK.Reflection
{
    public interface IReflectBuilder
    {
        // Methods
        object Create(Dictionary<string, string> parameters);
    }
}

namespace CLK.Reflection
{
    public class ReflectManager
    {
        // Fields
        private readonly IReflectProfileRepository _repository = null;


        // Constructors 
        public ReflectManager(IReflectProfileRepository repository)
        {
            #region Contracts

            if (repository == null) throw new ArgumentNullException();

            #endregion

            // Arguments
            _repository = repository;
        }


        // Methods
        private TEntity Create<TEntity>(ReflectProfile profile) where TEntity : class
        {
            #region Contracts

            if (profile == null) throw new ArgumentNullException();

            #endregion

            // Require
            if (string.IsNullOrEmpty(profile.ProfileName) == true) throw new InvalidOperationException();
            if (string.IsNullOrEmpty(profile.BuilderType) == true) throw new InvalidOperationException();

            // BuilderType
            Type builderType = Type.GetType(profile.BuilderType);
            if (builderType == null) throw new ArgumentException(String.Format("Action:{0}, State:{1}, BuilderType:{2}", "Reflect", "Fail to Access BuilderType", profile.BuilderType));

            // Builder
            IReflectBuilder builder = Activator.CreateInstance(builderType) as IReflectBuilder;
            if (builder == null) throw new ArgumentException(String.Format("Action:{0}, State:{1}, BuilderType:{2}", "Reflect", "Fail to Create Builder", profile.BuilderType));
            
            // Entity
            TEntity entity = builder.Create(profile.Parameters) as TEntity;
            if (entity == null) throw new ArgumentException(String.Format("Action:{0}, State:{1}, BuilderType:{2}", "Reflect", "Fail to Create Entity", profile.BuilderType));

            // Return
            return entity;
        }


        public IEnumerable<TEntity> CreateAll<TEntity>(string reflectSpace) where TEntity : class
        {
            #region Contracts

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();

            #endregion

            // Result
            List<TEntity> entityList = new List<TEntity>();

            // Create
            foreach (ReflectProfile profile in _repository.CreateAllProfile(reflectSpace))
            {
                TEntity entity = this.Create<TEntity>(profile);
                if (entity != null)
                {
                    entityList.Add(entity);
                }
            }

            // Return
            return entityList;
        }

        public TEntity Create<TEntity>(string reflectSpace) where TEntity : class
        {
            #region Contracts

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();

            #endregion

            // ProfileName
            string profileName = _repository.GetDefaultProfileName(reflectSpace);
            if (string.IsNullOrEmpty(profileName) == true) throw new ArgumentException(String.Format("Action:{0}, State:{1}, ReflectSpace:{2}", "Reflect", "Fail to Get DefaultProfileName", reflectSpace));

            // Return
            return this.Create<TEntity>(reflectSpace, profileName);
        }

        public TEntity Create<TEntity>(string reflectSpace, string profileName) where TEntity : class
        {
            #region Contracts

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();
            if (string.IsNullOrEmpty(profileName) == true) throw new ArgumentNullException();

            #endregion

            // Profile
            ReflectProfile profile = _repository.GetProfile(reflectSpace, profileName);
            if (profile == null) return default(TEntity);

            // Return
            return this.Create<TEntity>(profile);
        }        
    }    
}

ConfigReflectProfileRepository

在范例程序里，示范了IReflectProfileRepository的实作，这个实作使用App.config做为ReflectProfile的数据源。相关的程序代码如下，有兴趣的开发人员可以花点时间学习，在需要扩充IReflectProfileRepository的时候(例如：改用SQL存放)，就可以自行加入相关的实作。

namespace CLK.Reflection.Implementation
{
    public class ConfigReflectProfileRepository : IReflectProfileRepository
    {
        // Default
        public static string GetDefaultConfigFilename()
        {
            // Configuration
            System.Configuration.Configuration configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            if (configuration == null) throw new ArgumentNullException();

            // ConfigFilename
            string configFilename = configuration.FilePath;
            if (string.IsNullOrEmpty(configFilename) == true) throw new ArgumentNullException();

            // Return
            return configFilename;
        }


        // Fields
        private readonly string _configFilename = null;

        private System.Configuration.Configuration _configuration = null;


        // Constructors
        public ConfigReflectProfileRepository() : this(ConfigReflectProfileRepository.GetDefaultConfigFilename()) { }

        public ConfigReflectProfileRepository(string configFilename)
        {
            #region Require

            if (string.IsNullOrEmpty(configFilename) == true) throw new ArgumentNullException();

            #endregion

            // ConfigFilename
            _configFilename = configFilename;
        }


        // Methods
        private System.Configuration.Configuration CreateConfiguration()
        {
            if (_configuration == null)
            {
                if (_configFilename != null)
                {
                    ExeConfigurationFileMap configFileMap = new ExeConfigurationFileMap();
                    configFileMap.ExeConfigFilename = _configFilename;
                    _configuration = ConfigurationManager.OpenMappedExeConfiguration(configFileMap, ConfigurationUserLevel.None);
                }
                else
                {
                    _configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
                }
            }
            return _configuration;
        }

        private ConfigReflectProfileSection CreateSection(string reflectSpace)
        {
            #region Require

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();

            #endregion

            // Configuration
            System.Configuration.Configuration configuration = this.CreateConfiguration();
            if (configuration == null) throw new ArgumentException(String.Format("Action:{0}, State:{1}", "Reflect", "Fail to Create Configuration"));

            // Section
            ConfigReflectProfileSection section = configuration.GetSection(reflectSpace) as ConfigReflectProfileSection;
            if (section == null) throw new ArgumentException(String.Format("Action:{0}, State:{1}, ReflectSpace:{2}", "Reflect", "Fail to Create ConfigReflectProfileSection", reflectSpace));
            
            // Return
            return section;
        }
        

        public string GetDefaultProfileName(string reflectSpace)
        {
            #region Require

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();

            #endregion

            // Section
            ConfigReflectProfileSection section = this.CreateSection(reflectSpace);
            if (section == null) throw new MemberAccessException();

            // DefaultProfileName
            string defaultProfileName = section.DefaultProfileName;
            if (string.IsNullOrEmpty(defaultProfileName) == true) throw new ArgumentException(String.Format("Action:{0}, State:{1}, ReflectSpace:{2}", "Reflect", "Fail to Get DefaultProfileName", reflectSpace));
            
            // Return
            return defaultProfileName;
        }

        public ReflectProfile GetProfile(string reflectSpace, string profileName)
        {
            #region Require

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();

            #endregion

            // Result
            ReflectProfile profile = null;

            // Section
            ConfigReflectProfileSection section = this.CreateSection(reflectSpace);
            if (section == null) throw new MemberAccessException();

            // Element
            foreach (ConfigReflectProfileElement element in section.ProfileCollection)
            {
                if (element.ProfileName == profileName)
                {
                    // Profile
                    profile = new ReflectProfile();
                    profile.ProfileName = element.ProfileName;
                    profile.BuilderType = element.BuilderType;
                    foreach (string parameterKey in element.UnrecognizedAttributes.Keys)
                    {
                        profile.Parameters.Add(parameterKey, element.UnrecognizedAttributes[parameterKey]);
                    }
                    break;
                }
            }

            // Return
            return profile;
        }

        public IEnumerable<ReflectProfile> CreateAllProfile(string reflectSpace)
        {
            #region Require

            if (string.IsNullOrEmpty(reflectSpace) == true) throw new ArgumentNullException();

            #endregion

            // Result
            List<ReflectProfile> profileList = new List<ReflectProfile>();;

            // Section
            ConfigReflectProfileSection section = this.CreateSection(reflectSpace);
            if (section == null) throw new MemberAccessException();

            // Element
            foreach (ConfigReflectProfileElement element in section.ProfileCollection)
            {
                    // Profile
                     ReflectProfile profile = new ReflectProfile();
                    profile.ProfileName = element.ProfileName;
                    profile.BuilderType = element.BuilderType;
                    foreach (string parameterKey in element.UnrecognizedAttributes.Keys)
                    {
                        profile.Parameters.Add(parameterKey, element.UnrecognizedAttributes[parameterKey]);
                    }
                profileList.Add(profile);
            }

            // Return
            return profileList;
        }
    }
}

namespace CLK.Reflection.Implementation
{
    public sealed class ConfigReflectProfileSection : ConfigurationSection
    {
        // Properties
        [ConfigurationProperty("default", DefaultValue = "", IsRequired = false)]
        public string DefaultProfileName
        {
            get
            {
                return (string)base["default"];
            }
            set
            {
                base["default"] = value;
            }
        }

        [ConfigurationProperty("", IsDefaultCollection = true, IsRequired = false)]
        public ConfigReflectProfileElementCollection ProfileCollection
        {
            get
            {
                return (ConfigReflectProfileElementCollection)base[""];
            }
        }
    }

    public sealed class ConfigReflectProfileElementCollection : ConfigurationElementCollection
    {
        // Constructor
        public ConfigReflectProfileElementCollection() { }


        // Properties
        public override ConfigurationElementCollectionType CollectionType
        {
            get
            {
                return ConfigurationElementCollectionType.AddRemoveClearMap;
            }
        }


        // Methods  
        protected override ConfigurationElement CreateNewElement()
        {
            return new ConfigReflectProfileElement();
        }

        protected override object GetElementKey(ConfigurationElement element)
        {
            #region Contracts

            if (element == null) throw new ArgumentNullException();

            #endregion
            return ((ConfigReflectProfileElement)element).ProfileName;
        }


        public void Add(ConfigReflectProfileElement element)
        {
            #region Contracts

            if (element == null) throw new ArgumentNullException();

            #endregion
            this.BaseAdd(element);
        }

        public void Remove(string name)
        {
            this.BaseRemove(name);
        }        

        public bool Contains(string name)
        {
            #region Contracts

            if (string.IsNullOrEmpty(name) == true) throw new ArgumentNullException();

            #endregion
            if (this.BaseGet(name) != null)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        public ConfigReflectProfileElement GetByName(string name)
        {
            #region Contracts

            if (string.IsNullOrEmpty(name) == true) throw new ArgumentNullException();

            #endregion
            return (ConfigReflectProfileElement)this.BaseGet(name);
        }
    }

    public sealed class ConfigReflectProfileElement : UnrecognizedAttributeConfigurationElement
    {
        // Constructor
        public ConfigReflectProfileElement()
        {
            // Default
            this.ProfileName = string.Empty;
            this.BuilderType = string.Empty;
        }


        // Properties
        [ConfigurationProperty("name", IsKey = true, IsRequired = true)]
        public string ProfileName
        {
            get
            {
                return Convert.ToString(base["name"]);
            }
            set
            {
                base["name"] = value;
            }
        }

        [ConfigurationProperty("builderType", IsKey = true, IsRequired = false)]
        public string BuilderType
        {
            get
            {
                return Convert.ToString(base["builderType"]);
            }
            set
            {
                base["builderType"] = value;
            }
        }
    }
}

使用

DisplayWorker

接着撰写一个虚拟的IDisplayWorker来示范如何套用Rough Dependency Injection。首先在项目内建立IDisplayWorker，这个IDisplayWorker很简单的只开放一个Show函式让系统使用。接着建立两个实作IDisplayWorker的对象，这两个对象就是后续要用来注入系统的对象。到这边可以发现，套用Rough Dependency Injection注入的对象，不会有额外的相依，只要完成自己应有的职责就可以。

namespace TestProject
{
    public interface IDisplayWorker
    {
        // Methods
        void Show();
    }

    public class AAADisplayWorker : IDisplayWorker
    {
        // Properties
        public string AAA { get; set; }


        // Methods
        public void Show()
        {
            Console.WriteLine(this.AAA);
        }
    }

    public class BBBDisplayWorker : IDisplayWorker
    {
        // Properties
        public int BBB { get; set; }


        // Methods
        public void Show()
        {
            Console.WriteLine(this.BBB);
        }
    }
}

DisplayWorkerBuilder

要让注入对象，不会有额外的相依，也是要付出代价。要另外建立一层Builder，用来生成注入对象，以及隔离注入对象与Rough Dependency Injection的相依。

namespace TestProject
{
    public class AAADisplayWorkerBuilder : IReflectBuilder
    {
        // Methods
        public object Create(Dictionary<string, string> parameters)
        {
            AAADisplayWorker worker = new AAADisplayWorker();
            worker.AAA = Convert.ToString(parameters["AAA"]);
            return worker;
        }
    }

    public class BBBDisplayWorkerBuilder : IReflectBuilder
    {
        // Methods
        public object Create(Dictionary<string, string> parameters)
        {
            BBBDisplayWorker worker = new BBBDisplayWorker();
            worker.BBB = Convert.ToInt32(parameters["BBB"]);
            return worker;
        }
    }
}

执行

最后建立使用IDisplayWorker的范例RoughDependencyInjectionSample，在RoughDependencyInjectionSample内透过ReflectManager搭配App.config里的设定，为系统注入两个IDisplayWorker实作让系统使用。

<?xml version="1.0" encoding="utf-8" ?>
<configuration>

  <!-- ConfigSections -->
  <configSections>
    <sectionGroup name="testProject">
      <section name="displayWorker" type="CLK.Reflection.Implementation.ConfigReflectProfileSection, CLK" />
    </sectionGroup>
  </configSections>

  <!-- TestProject -->
  <testProject>
    <displayWorker>
      <add name="AAA" builderType="TestProject.AAADisplayWorkerBuilder, TestProject" AAA="Clark=_=y-~" />
      <add name="BBB" builderType="TestProject.BBBDisplayWorkerBuilder, TestProject" BBB="1234" />
    </displayWorker>
  </testProject>

</configuration>

namespace TestProject
{
    class Program
    {
        static void Main(string[] args)
        {
            // ReflectManager
            ReflectManager reflectManager = new ReflectManager(new ConfigReflectProfileRepository());

            // CreateAll
            foreach (IDisplayWorker worker in reflectManager.CreateAll<IDisplayWorker>(@"testProject/displayWorker"))
            {
                // Show
                worker.Show();
            }

            // End
            Console.ReadLine();
        }
    }
}