【最简单IOC容器实现】实现一个最简单的IOC容器

前面DebugLZQ的两篇博文：

浅谈IOC--说清楚IOC是什么

IoC Container Benchmark - Performance comparison

在浅谈IOC--说清楚IOC是什么中，DebugLZQ介绍了什么是到底什么是IOC/DI，再复习一下，那么到底什么是IOC呢？

就像Martin Flower所说的：依赖对象的获得过程被反转了，即由之前是consumer主动去new，变成consumer向IOC容器去要，然后由IOC容器注入依赖对象。

这个回答非常的口语化，但IOC的思想确实就是这样。

然后IoC Container Benchmark - Performance comparison对各种现有的IOC容器的性能做了比较。

感兴趣的博友可以看下前面的两篇博文，会有助于你理解这一篇。

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下面我们就来实现一个最简单的IOC容器。

我们要做的事情是：从一个地方获得输入，然后将这个输入再Write出去。

作为对比，首先来看一下不用IOC，即consumer主动去new的情况：

using System;

namespace Normal
{
    public interface IReader
    {
        string Read();
    }

    public interface IWriter
    {
        void Write(string data);
    }

    public class ReadKeyboard : IReader
    {
        public string Read()
        {
            return "code to read from keyboard and return as string";
        }
    }

    public class ReadScanner : IReader
    {
        public string Read()
        {
            return "code to read from scanner and return as string";
        }
    }

    public class WritePrinter : IWriter
    {
        public void Write(string data)
        {            
            Console.WriteLine("code to write to the printer: "+data);
        }     
    }

    public class WriteFlashDisk : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the flash disk: " + data);           
        }
    }

    public class Copy
    {
        public void DoWork(IReader reader,IWriter writer)
        {
            string data = reader.Read();
            writer.Write(data);
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            Copy copy = new Copy();
            copy.DoWork(new ReadKeyboard(),new WritePrinter());//依赖对象获得时多个依赖,应当用IOCContainer解耦
        }
    }
}

撇去Test类不看，以上代码堪称clean，完美符合SOLID（FxCop、StyleCop等默认rules就不谈了）。
Test类依然是"new对象"，这是问题的所在。

---------------------------------------------------------------

进入正题：实现这个最简单的IOC容器！

为上面的代码添加一个自定义的IOC容器类，其核心思想是由反射去构建依赖对象。

这个IOC容器的代码如下：

    /// <summary>
    /// My own IocContainer
    /// http://www.cnblogs.com/DebugLZQ
    /// </summary>
    public class Container
    {
        private Dictionary<Type, Type> iocMap = new Dictionary<Type, Type>();

        public void Register<TypetoResolve, ResolvedType>()
        {
            if (iocMap.ContainsKey(typeof(TypetoResolve)))
            {
                throw new Exception(string.Format("Type {0} already registered.", typeof(TypetoResolve).FullName));
            }
            iocMap.Add(typeof(TypetoResolve), typeof(ResolvedType));
        }

        public T Resolve<T>()
        {
            return (T)Resolve(typeof(T));
        }

        public object Resolve(Type typeToResolve)
        {
            //Find the registered type for typeToResolve
            if (!iocMap.ContainsKey(typeToResolve))
            {
                throw new Exception(string.Format("Can't resolve type {0}. Type is not registered.", typeToResolve.FullName));
            }
            Type resolvedType = iocMap[typeToResolve];
            //Try to construct the object
            //step-1: find the constructor. 
            ConstructorInfo ctorInfo = resolvedType.GetConstructors().First();
            //step-2:find the parameters for the constructor and try to resolve those.
            List<ParameterInfo> paramsInfo = ctorInfo.GetParameters().ToList();
            List<object> resolvedParams = new List<object>();
            foreach (ParameterInfo param in paramsInfo)
            {
                Type t = param.ParameterType;
                object res = Resolve(t);
                resolvedParams.Add(res);
            }
            //step-3:using reflection invoke constructor to create the object
            object retObject = ctorInfo.Invoke(resolvedParams.ToArray());
            return retObject;
        }
    }

--------------------------------------------------------------------

其他部分保持不变(Test类除外)。

如何使用这个IOC容器呢？

给出完整代码，如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace ContainerDI2_Test
{
    public interface IReader
    {
        string Read();
    }

    public interface IWriter
    {
        void Write(string data);
    }

    public class ReadKeyboard : IReader
    {
        public string Read()
        {
            return "code to read from keyboard and return as string";
        }
    }

    public class ReadScanner : IReader
    {
        public string Read()
        {
            return "code to read from scanner and return as string";
        }
    }

    public class WritePrinter : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the printer: " + data);
        }
    }

    public class WriteFlashDisk : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the flash disk: " + data);
        }
    }

    public class Copy
    {
        public void DoWork(IReader reader, IWriter writer)
        {
            string data = reader.Read();
            writer.Write(data);
        }
    }

    /// <summary>
    /// My own IocContainer
    /// http://www.cnblogs.com/DebugLZQ
    /// </summary>
    public class Container
    {
        private Dictionary<Type, Type> iocMap = new Dictionary<Type, Type>();

        public void Register<TypetoResolve, ResolvedType>()
        {
            if (iocMap.ContainsKey(typeof(TypetoResolve)))
            {
                throw new Exception(string.Format("Type {0} already registered.", typeof(TypetoResolve).FullName));
            }
            iocMap.Add(typeof(TypetoResolve), typeof(ResolvedType));
        }

        public T Resolve<T>()
        {
            return (T)Resolve(typeof(T));
        }

        public object Resolve(Type typeToResolve)
        {
            //Find the registered type for typeToResolve
            if (!iocMap.ContainsKey(typeToResolve))
            {
                throw new Exception(string.Format("Can't resolve type {0}. Type is not registered.", typeToResolve.FullName));
            }
            Type resolvedType = iocMap[typeToResolve];
            //Try to construct the object
            //step-1: find the constructor. 
            ConstructorInfo ctorInfo = resolvedType.GetConstructors().First();
            //step-2:find the parameters for the constructor and try to resolve those.
            List<ParameterInfo> paramsInfo = ctorInfo.GetParameters().ToList();
            List<object> resolvedParams = new List<object>();
            foreach (ParameterInfo param in paramsInfo)
            {
                Type t = param.ParameterType;
                object res = Resolve(t);
                resolvedParams.Add(res);
            }
            //step-3:using reflection invoke constructor to create the object
            object retObject = ctorInfo.Invoke(resolvedParams.ToArray());
            return retObject;
        }
    }

    class Test
    {
        static void DIRegistration(Container container)
        {
            container.Register<IReader, ReadKeyboard>();
            container.Register<IWriter, WritePrinter>();
        }

        static void Main(string[] args)
        {
            Container container = new Container();
            DIRegistration(container);

            Copy copy = new Copy();
            copy.DoWork(container.Resolve<IReader>(), container.Resolve<IWriter>());//依赖于IOC容器了
        }
    }
}

 可以和前面new那个代码比较下，看看两者的区别。

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当然DebugLZQ为了更清楚的说明代码问题，因而没有进行分层，当然你也可以把工程写成这样：

 分层的好处是结构清晰。

以上两段代码，均可正常运行，运行结果相同，其运行截图如下：

 --------------------------------------------------------------------------------

当然根据个人编码习惯，我们也可以把Copy类写成这样

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace ContainerDI
{
    public interface IReader
    {
        string Read();
    }

    public interface IWriter
    {
        void Write(string data);
    }

    public class ReadKeyboard : IReader
    {
        public string Read()
        {
            return "code to read from keyboard and return as string";
        }
    }

    public class ReadScanner : IReader
    {
        public string Read()
        {
            return "code to read from scanner and return as string";
        }
    }

    public class WritePrinter : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the printer: " + data);
        }
    }

    public class WriteFlashDisk : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the flash disk: " + data);
        }
    }

    public class Copy
    {
        private Container _container; 
        private IReader _reader;
        private IWriter _writer;//也可以是具体类型

        public Copy(Container container)
        {
            this._container = container;
            this._reader = _container.Resolve<IReader>();
            this._writer = _container.Resolve<IWriter>();
        }

        public void DoWork()
        {
            string data = _reader.Read();
            _writer.Write(data);
        }
    }

    /// <summary>
    /// My own IocContainer
    /// </summary>
    public class Container
    {
        private Dictionary<Type, Type> iocMap = new Dictionary<Type, Type>();

        public void Register<TypetoResolve, ResolvedType>()
        {
            if (iocMap.ContainsKey(typeof(TypetoResolve)))
            {
                throw new Exception(string.Format("Type {0} already registered.",typeof(TypetoResolve).FullName));
            }
            iocMap.Add(typeof(TypetoResolve), typeof(ResolvedType));
        }

        public T Resolve<T>()
        {
            return (T)Resolve(typeof(T));
        }
        
        public object Resolve(Type typeToResolve)
        {
            //Find the registered type for typeToResolve
            if(!iocMap.ContainsKey(typeToResolve))
            {
                throw new Exception(string.Format("Can't resolve type {0}. Type is not registered.",typeToResolve.FullName));
            }
            Type resolvedType = iocMap[typeToResolve];
            //Try to construct the object
            //step-1: find the constructor. 
            ConstructorInfo ctorInfo = resolvedType.GetConstructors().First();
            //step-2:find the parameters for the constructor and try to resolve those.
            List<ParameterInfo> paramsInfo = ctorInfo.GetParameters().ToList();
            List<object> resolvedParams = new List<object>();
            foreach (ParameterInfo param in paramsInfo)
            {
                Type t = param.ParameterType;
                object res = Resolve(t);
                resolvedParams.Add(res);
            }
            //step-3:using reflection invoke constructor to create the object
            object retObject = ctorInfo.Invoke(resolvedParams.ToArray());
            return retObject;
        }
    }

    class Test
    {
        static void DIRegistration(Container container)
        {
            container.Register<IReader, ReadKeyboard>();
            container.Register<IWriter, WritePrinter>();
        }

        static void Main(string[] args)
        {
            Container container = new Container();
            DIRegistration(container);

            Copy copy = new Copy(container);
            copy.DoWork();
        }
    }
}

也可以写成这样：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;

namespace ContainerDI2
{
    public interface IReader
    {
        string Read();
    }

    public interface IWriter
    {
        void Write(string data);
    }

    public class ReadKeyboard : IReader
    {
        public string Read()
        {
            return "code to read from keyboard and return as string";
        }
    }

    public class ReadScanner : IReader
    {
        public string Read()
        {
            return "code to read from scanner and return as string";
        }
    }

    public class WritePrinter : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the printer: " + data);
        }
    }

    public class WriteFlashDisk : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the flash disk: " + data);
        }
    }

    public class Copy
    {        
        private IReader _reader;
        private IWriter _writer;//也可以是具体类型

        public Copy(IReader reader,IWriter writer)
        {

            this._reader = reader;
            this._writer = writer;
        }

        public void DoWork()
        {
            string data = _reader.Read();
            _writer.Write(data);
        }
    }

    /// <summary>
    /// My own IocContainer
    /// http://www.cnblogs.com/DebugLZQ
    /// </summary>
    public class Container
    {
        private Dictionary<Type, Type> iocMap = new Dictionary<Type, Type>();

        public void Register<TypetoResolve, ResolvedType>()
        {
            if (iocMap.ContainsKey(typeof(TypetoResolve)))
            {
                throw new Exception(string.Format("Type {0} already registered.", typeof(TypetoResolve).FullName));
            }
            iocMap.Add(typeof(TypetoResolve), typeof(ResolvedType));
        }

        public T Resolve<T>()
        {
            return (T)Resolve(typeof(T));
        }

        public object Resolve(Type typeToResolve)
        {
            //Find the registered type for typeToResolve
            if (!iocMap.ContainsKey(typeToResolve))
            {
                throw new Exception(string.Format("Can't resolve type {0}. Type is not registered.", typeToResolve.FullName));
            }
            Type resolvedType = iocMap[typeToResolve];
            //Try to construct the object
            //step-1: find the constructor. 
            ConstructorInfo ctorInfo = resolvedType.GetConstructors().First();
            //step-2:find the parameters for the constructor and try to resolve those.
            List<ParameterInfo> paramsInfo = ctorInfo.GetParameters().ToList();
            List<object> resolvedParams = new List<object>();
            foreach (ParameterInfo param in paramsInfo)
            {
                Type t = param.ParameterType;
                object res = Resolve(t);
                resolvedParams.Add(res);
            }
            //step-3:using reflection invoke constructor to create the object
            object retObject = ctorInfo.Invoke(resolvedParams.ToArray());
            return retObject;
        }
    }

    class Test
    {
        static void DIRegistration(Container container)
        {
            container.Register<IReader, ReadKeyboard>();
            container.Register<IWriter, WritePrinter>();
        }

        static void Main(string[] args)
        {
            Container container = new Container();
            DIRegistration(container);

            Copy copy = new Copy(container.Resolve<IReader>(),container.Resolve<IWriter>());
            copy.DoWork();
        }
    }
}

程序均可正常工作，运行结果与前面相同。 

至此，最简单的IOC容器完成。

----------------------------------------------------------------------

-----------------------------------------------------------------------

上面的IOC容器，每次都重新构建一个新的对象。

我们稍加改造：

如果我们需要维持对象对象的某个状态(如对象的创建时刻等)，也就是说给给IOC容器构建的对象加上生命周期。那我们该怎么办呢？

思路很简单：对于需要维持状态的对象，IOC第一次构建以后，先存着，后来有要用的直接返回前面构建的那个。

把我们的思路转换成代码，如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace ContainerDIWithLifeOption
{
    public interface IReader
    {
        string Read();
    }

    public interface IWriter
    {
        void Write(string data);
    }

    public class ReadKeyboard : IReader
    {
        public string Read()
        {
            return "code to read from keyboard and return as string";
        }
    }

    public class ReadScanner : IReader
    {
        public string Read()
        {
            return "code to read from scanner and return as string";
        }
    }

    public class WritePrinter : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the printer: " + data);
        }
    }

    public class WriteFlashDisk : IWriter
    {
        public void Write(string data)
        {
            Console.WriteLine("code to write to the flash disk: " + data);
        }
    }

    public class Copy
    {
        private IReader _reader;
        private IWriter _writer;//也可以是具体类型

        public Copy(IReader reader, IWriter writer)
        {

            this._reader = reader;
            this._writer = writer;
        }

        public void DoWork()
        {
            string data = _reader.Read();
            _writer.Write(data);
        }
    }

    public  enum LifeTimeOptions
    {
        TransientLifeTimeOption,
        ContainerControlledLifeTimeOption
    }

    public class ResolvedTypeWithLifeTimeOptions
    {
        public Type ResolvedType { get; set; }
        public LifeTimeOptions LifeTimeOption { get; set; }
        public object InstanceValue { get; set; }

        public ResolvedTypeWithLifeTimeOptions(Type resolvedType)
        {
            ResolvedType = resolvedType;
            LifeTimeOption = LifeTimeOptions.TransientLifeTimeOption;
            InstanceValue = null;
        }

        public ResolvedTypeWithLifeTimeOptions(Type resolvedType, LifeTimeOptions lifeTimeOption)
        {
            ResolvedType = resolvedType;
            LifeTimeOption = lifeTimeOption;
            InstanceValue = null;
        }
    }

    public class Container
    {
        private Dictionary<Type, ResolvedTypeWithLifeTimeOptions>
            iocMap = new Dictionary<Type, ResolvedTypeWithLifeTimeOptions>();

        public void Register<T1, T2>()
        {
            Register<T1, T2>(LifeTimeOptions.TransientLifeTimeOption);
        }

        public void Register<T1, T2>(LifeTimeOptions lifeTimeOption)
        {
            if (iocMap.ContainsKey(typeof (T1)))
            {
                throw new Exception(string.Format("Type {0} already registered.", typeof (T1).FullName));
            }
            ResolvedTypeWithLifeTimeOptions targetType = new ResolvedTypeWithLifeTimeOptions(typeof (T2),
                                                                                             lifeTimeOption);
            iocMap.Add(typeof (T1), targetType);
        }

        public T Resolve<T>()
        {
            return (T) Resolve(typeof (T));
        }

        public object Resolve(Type typeToResolve)
        {
            // Find the registered type for typeToResolve
            if (!iocMap.ContainsKey(typeToResolve))
                throw new Exception(string.Format("Can't resolve {0}.Type is not registered.", typeToResolve.FullName));

            ResolvedTypeWithLifeTimeOptions resolvedType = iocMap[typeToResolve];

            // Step-1: If LifeTimeOption is ContainerControlled and there is 
            //already an instance created then return the created instance.
            if (resolvedType.LifeTimeOption ==
                LifeTimeOptions.ContainerControlledLifeTimeOption&&
                resolvedType.InstanceValue != null)
                return resolvedType.InstanceValue;

            // Try to construct the object
            // Step-2: find the constructor 
            //(ideally first constructor if multiple constructors present for the type)
            ConstructorInfo ctorInfo = resolvedType.ResolvedType.GetConstructors().First();

            // Step-3: find the parameters for the constructor and try to resolve those
            List<ParameterInfo> paramsInfo = ctorInfo.GetParameters().ToList();
            List<object> resolvedParams = new List<object>();
            foreach (ParameterInfo param in paramsInfo)
            {
                Type t = param.ParameterType;
                object res = Resolve(t);
                resolvedParams.Add(res);
            }

            // Step-4: using reflection invoke constructor to create the object
            object retObject = ctorInfo.Invoke(resolvedParams.ToArray());

            resolvedType.InstanceValue = retObject;

            return retObject;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Container container = new Container();

            DIRegistration(container);

            Copy copy = new Copy(container.Resolve<IReader>(),container.Resolve<IWriter>());
            copy.DoWork();
            Console.ReadLine();

            Copy copy2 = new Copy(container.Resolve<IReader>(), container.Resolve<IWriter>());
            copy2.DoWork();
            Console.ReadLine();
        }

        private static void DIRegistration(Container container)
        {
            container.Register<IReader, ReadKeyboard>(LifeTimeOptions.ContainerControlledLifeTimeOption);
            container.Register<IWriter, WritePrinter>(LifeTimeOptions.TransientLifeTimeOption);
        }
    }
}

程序运行如下：

至此，正文完结。

参考：

• CSDN: 架构师之路(39)---IoC框架
• EagleFish(邢瑜琨)  深度理解依赖注入（Dependence Injection）
• Martin Flower  Inversion of Control Containers and the Dependency Injection pattern
• 黄忠成　Object Builder Application Block
• Dependency Inversion Principle, IoC Container & Dependency Injection (Part - 1)
• Dependency Inversion Principle, IoC Container & Dependency Injection (Part - 2)
• Dependency Inversion Principle, IoC Container, and Dependency Injection (Part - 3)
• Dependency Inversion Principle, IoC Container, and Dependency Injection (Part - 4)
• http://www.codeproject.com/Articles/538536/A-curry-of-Dependency-Inversion-Principle-DIP-Inve
• http://www.jamesshore.com/Blog/Dependency-Injection-Demystified.html
• http://www.pluralsight.com/training
• http://www.oodesign.com
• http://blog.architexa.com/2010/05/types-of-dependency-injection/
• http://www.codeproject.com/Articles/495019/Dependency-Inversion-Principle-and-the-Dependency
• and so on

忽然想起一句话，不知是在哪里看到的了，大概意思是：不能用自己语言讲清楚的东西---你没掌握，技术这个东西不存在所谓的“只可意会不可言传”。

希望对你有帮助，老鸟、大虾、高手等绕过，轻拍~

Update:请关注后续博文：MEF随笔索引