一說到反射，很多人都想到了性能，更有甚者直接說“慎用反射，遺患無窮”，“用反射，感覺怎么像是退步啊～”，看到這種言論，直接把反射妖魔化了，如果這種言論長此以往，勢必會對很多對反射初學者造成負面影響。反射是一把雙刃劍，看你怎樣使用了，下面我就用代碼說話。

class TestEntity { }

　　1. 手工創建TestEntity?

[TestInfo(Category = "Class.Constructor", Name = "Direct")]
class DirectInvokeMode:IRunable
{
public void Run()
{
new TestEntity();
}
}

?? ? 2. 反射創建TestEntity?

[TestInfo(Category = "Class.Constructor", Name = "Reflect")]
class ReflectInvokeMode : IRunable
{
public void Run()
{
Activator.CreateInstance(typeof(TestEntity));
}
}

　　3. 泛型反射創建TestEntity

[TestInfo(Category = "Class.Constructor", Name = "GenericReflect")]
class GenericReflectInvokeMode : IRunable
{
public void Run()
{
Activator.CreateInstance<TestEntity>();
}
}

　　4. Generic 直接創建

[TestInfo(Category = "Class.Constructor", Name = "Generic Create")]
class GenericCreateInvokeMode : IRunable
{
public void Run()
{
Create<TestEntity>();
}

static T Create<T>() where T : new()
{
return new T();
}
} 5. Emit創建 [TestInfo(Category = "Class.Constructor", Name = "Emit")]
class EmitInvokeMode : IRunable
{
static readonly ConstructorHandler Ctor = typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator();

public void Run()
{
Ctor();
}
}

　　6. 不緩存Emit的創建

[TestInfo(Category = "Class.Constructor", Name = "NoCacheEmit")]
class NoCacheEmitInvokeMode : IRunable
{
public void Run()
{
typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator()();
}
}

　　測試程序：（執行10萬次創建Class對象）

foreach (var item in Mappers)
CodeTimer.Time(item.Metadata.Category + "->" + item.Metadata.Name, 100000, () => item.Value.Run());

輸出結果：

------ Test started: Assembly: NLite.Test.dll ------


Class.Constructor->Direct
Time Elapsed: 5ms
CPU Cycles: 0
Gen 0: 1
Gen 1: 0
Gen 2: 0

Class.Constructor->Reflect
Time Elapsed: 320ms
CPU Cycles: 2,968,750
Gen 0: 1
Gen 1: 0
Gen 2: 0

Class.Constructor->GenericReflect
Time Elapsed: 147ms
CPU Cycles: 1,250,000
Gen 0: 1
Gen 1: 0
Gen 2: 0

Class.Constructor->Generic Create
Time Elapsed: 159ms
CPU Cycles: 1,406,250
Gen 0: 1
Gen 1: 0
Gen 2: 0

Class.Constructor->Emit
Time Elapsed: 6ms
CPU Cycles: 0
Gen 0: 2
Gen 1: 0
Gen 2: 0

Class.Constructor->NoCacheEmit
Time Elapsed: 12,786ms
CPU Cycles: 119,218,750
Gen 0: 162
Gen 1: 81
Gen 2: 0

1 passed, 0 failed, 0 skipped, took 67.77 seconds (NUnit 2.5.5).

　　性能比較結果應該是一目了然了！

?? ? ?附上源代碼：

using System; using System.Collections.Generic; using System.Linq; using System.Text; using NUnit.Framework; using System.Reflection; using NLite.Reflection;namespace NLite.Test.Reflection {[Contract]public interface IRunable{void Run();}//測試器元數據public interface ITestInfo{//目錄string Category { get; }//名稱string Name { get; }}//映射器元數據注解[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)][MetadataAttributeAttribute]public class TestInfoAttribute : ComponentAttribute{public string Category { get; set; }public string Name { get; set; }}[TestFixture]public class SpecBase{public SpecBase(){}[SetUp]public void SetUp(){Given();When();}public virtual void Given() { }public virtual void When(){}[Test]public void Test(){}}public abstract class PerformanceSpecBase : SpecBase{[InjectMany]protected Lazy<IRunable, ITestInfo>[] Mappers;protected abstract void RegisterComponents();public virtual int Times{get { return 100000; }}public override void Given(){RegisterComponents();ServiceRegistry.Compose(this);}public override void When(){for (int i = 0; i < 3; i++){foreach (var item in Mappers)CodeTimer.Time(item.Metadata.Category + "->" + item.Metadata.Name, Times, () => item.Value.Run());}}}public class InvokeConstructorPerformanceSpec : PerformanceSpecBase{class TestEntity { }protected override void RegisterComponents(){ServiceRegistry.Register<DirectInvokeMode>().Register<ReflectInvokeMode>().Register<GenericReflectInvokeMode>().Register <GenericCreateInvokeMode>().Register<EmitInvokeMode>().Register < NoCacheEmitInvokeMode>().Register < GenericReflectInvokeMode2>();}[TestInfo(Category = "Class.Constructor", Name = "Direct")]class DirectInvokeMode:IRunable{public void Run(){new TestEntity();}}[TestInfo(Category = "Class.Constructor", Name = "Reflect")]class ReflectInvokeMode : IRunable{public void Run(){Activator.CreateInstance(typeof(TestEntity));}}[TestInfo(Category = "Class.Constructor", Name = "GenericReflect")]class GenericReflectInvokeMode : IRunable{public void Run(){Activator.CreateInstance<TestEntity>();}}[TestInfo(Category = "Class.Constructor", Name = "Reflect->Reflect")]class GenericReflectInvokeMode2 : IRunable{static readonly MethodInfo CreateMethod = typeof(Activator).GetMethod("CreateInstance", Type.EmptyTypes).MakeGenericMethod(typeof(TestEntity));public void Run(){CreateMethod.Invoke(null,null);}}[TestInfo(Category = "Class.Constructor", Name = "Generic Create")]class GenericCreateInvokeMode : IRunable{public void Run(){Create<TestEntity>();}static T Create<T>() where T : new(){return new T();}}[TestInfo(Category = "Class.Constructor", Name = "Emit")]class EmitInvokeMode : IRunable{static readonly ConstructorHandler Ctor = typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator();public void Run(){Ctor();}}[TestInfo(Category = "Class.Constructor", Name = "NoCacheEmit")]class NoCacheEmitInvokeMode : IRunable{public void Run(){typeof(TestEntity).GetConstructor(Type.EmptyTypes).GetCreator()();}}}}

?? ? ?最后給大家一個思考題：Struct 創建性能大比拼的結果是怎樣的？（注意Struct是值類型，Class是引用類型，值類型是分配在棧上的，引用類型是分配在堆上的）

轉載于:https://www.cnblogs.com/netcasewqs/archive/2011/04/18/2019999.html

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