前面DebugLZQ的兩篇博文：
IoC Container Benchmark - Performance comparison
在淺談IOC--說清楚IOC是什么中，DebugLZQ介紹了什么是到底什么是IOC/DI，再復習一下，那么到底什么是IOC呢？
就像Martin Flower所說的：依賴對象的獲得過程被反轉了，即由之前是consumer主動去new，變成consumer向IOC容器去要，然后由IOC容器注入依賴對象。
這個回答非常的口語化，但IOC的思想確實就是這樣。
然后IoC Container Benchmark - Performance comparison對各種現有的IOC容器的性能做了比較。
感興趣的博友可以看下前面的兩篇博文，會有助於你理解這一篇。
-------------------------------------------------------------------------------------------
下面我們就來實現一個最簡單的IOC容器。
我們要做的事情是：從一個地方獲得輸入，然后將這個輸入再Write出去。
作為對比，首先來看一下不用IOC，即consumer主動去new的情況：
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());//依賴對象獲得時多個依賴,應當用IOCContainer解耦 } } }
撇去Test類不看，以上代碼堪稱clean，完美符合SOLID（FxCop、StyleCop等默認rules就不談了）。
Test類依然是"new對象"，這是問題的所在。
---------------------------------------------------------------
進入正題：實現這個最簡單的IOC容器！
為上面的代碼添加一個自定義的IOC容器類，其核心思想是由反射去構建依賴對象。
這個IOC容器的代碼如下：
/// <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; } }
--------------------------------------------------------------------
其他部分保持不變(Test類除外)。
如何使用這個IOC容器呢？
給出完整代碼，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>());//依賴於IOC容器了 } } }
可以和前面new那個代碼比較下，看看兩者的區別。
-----------------------------------------------------------------
當然DebugLZQ為了更清楚的說明代碼問題，因而沒有進行分層，當然你也可以把工程寫成這樣：
分層的好處是結構清晰。
以上兩段代碼，均可正常運行，運行結果相同，其運行截圖如下：
--------------------------------------------------------------------------------
當然根據個人編碼習慣，我們也可以把Copy類寫成這樣
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;//也可以是具體類型 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(); } } }
也可以寫成這樣：
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;//也可以是具體類型 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，運行結果與前面相同。
至此，最簡單的IOC容器完成。
----------------------------------------------------------------------
-----------------------------------------------------------------------
上面的IOC容器，每次都重新構建一個新的對象。
我們稍加改造：
如果我們需要維持對象對象的某個狀態(如對象的創建時刻等)，也就是說給給IOC容器構建的對象加上生命周期。那我們該怎么辦呢？
思路很簡單：對於需要維持狀態的對象，IOC第一次構建以后，先存着，后來有要用的直接返回前面構建的那個。
把我們的思路轉換成代碼，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;//也可以是具體類型 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); } } }
程序運行如下：
至此，正文完結。
參考：
- CSDN: 架構師之路(39)---IoC框架
- EagleFish(邢瑜琨) 深度理解依賴注入（Dependence Injection）
- Martin Flower Inversion of Control Containers and the Dependency Injection pattern
- 黃忠成 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
忽然想起一句話，不知是在哪里看到的了，大概意思是：不能用自己語言講清楚的東西---你沒掌握，技術這個東西不存在所謂的“只可意會不可言傳”。
希望對你有幫助，老鳥、大蝦、高手等繞過，輕拍~
Update:請關注后續博文：MEF隨筆索引