Emit：动态给一个类型添加Attribute
下面这段代码整理自sl4的官方文档，已经加了详细的注释，相信大家都能看明白：
using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Threading;
namespace CustomAttributeBuilderSample
{
public class DemoClass
{
static void Main(string[] args)
{
//得到新类型
Type myType = BuildTypeWithCustomAttributesOnMethod();
//创建myType的实例
object myInstance = Activator.CreateInstance(myType);
//获取myType上应用的所有Attribute
object[] customAttrs = myType.GetCustomAttributes(true);
Console.WriteLine("Custom Attributes for Type 'MyType':" + "\n");
object attrVal = null;
foreach (object customAttr in customAttrs)
{
//获取ClassCreatorAttribute中的Creator属性值
attrVal = typeof(ClassCreatorAttribute).InvokeMember("Creator", BindingFlags.GetProperty, null, customAttr, new object[] { });
Console.WriteLine(String.Format("-- Attribute: [{0} = \"{1}\"]", customAttr, attrVal) + "\n");
}
Console.WriteLine("Custom Attributes for Method 'HelloWorld()' in 'MyType':" + "\n");
//获取myType中的HelloWorld方法上的所有Attribute
customAttrs = myType.GetMember("HelloWorld")[0].GetCustomAttributes(true);
foreach (object customAttr in customAttrs)
{
//获取DateLastUpdatedAttribute的DateUpdated属性值
attrVal = typeof(DateLastUpdatedAttribute).InvokeMember("DateUpdated", BindingFlags.GetProperty, null, customAttr, new object[] { });
Console.WriteLine(String.Format("-- Attribute: [{0} = \"{1}\"]", customAttr, attrVal) + "\n");
}
Console.WriteLine("---" + "\n");
//动态调用myType实例中的HelloWorld方法
Console.WriteLine(myType.InvokeMember("HelloWorld", BindingFlags.InvokeMethod, null, myInstance, new object[] { }) + "\n");
Console.ReadKey();
}
/// <summary>
/// 创建一个应用了ClassCreatorAttribute、DateLastUpdatedAttribute的类型
/// </summary>
/// <returns></returns>
public static Type BuildTypeWithCustomAttributesOnMethod()
{
AppDomain currentDomain = Thread.GetDomain();
AssemblyName myAsmName = new AssemblyName();
myAsmName.Name = "MyAssembly";
//动态创建一个程序集
AssemblyBuilder myAsmBuilder = currentDomain.DefineDynamicAssembly(myAsmName, AssemblyBuilderAccess.Run);
//动态创建一个模块
ModuleBuilder myModBuilder = myAsmBuilder.DefineDynamicModule("MyModule");
//动态创建一个类型：MyType
TypeBuilder myTypeBuilder = myModBuilder.DefineType("MyType", TypeAttributes.Public);
//定义构造器参数
Type[] ctorParams = new Type[] { typeof(string) };
//获取构造器信息
ConstructorInfo classCtorInfo = typeof(ClassCreatorAttribute).GetConstructor(ctorParams);
//动态创建ClassCreatorAttribute
CustomAttributeBuilder myCABuilder = new CustomAttributeBuilder(
classCtorInfo,
new object[] { "Joe Programmer" });
//将上面动态创建的Attribute附加到(动态创建的)类型MyType
myTypeBuilder.SetCustomAttribute(myCABuilder);
//动态创建一个无返回值，无参数的，公有方法HelloWorld
MethodBuilder myMethodBuilder = myTypeBuilder.DefineMethod("HelloWorld", MethodAttributes.Public, null, new Type[] { });
ctorParams = new Type[] { typeof(string) };
//获取DateLastUpdatedAttribute的构造函数信息
classCtorInfo = typeof(DateLastUpdatedAttribute).GetConstructor(ctorParams);
//动态创建DateLastUpdatedAttribute
CustomAttributeBuilder myCABuilder2 = new CustomAttributeBuilder(
classCtorInfo,
new object[] { DateTime.Now.ToString() });
//将上面动态创建的Attribute附加到(动态创建的)方法HelloWorld
myMethodBuilder.SetCustomAttribute(myCABuilder2);
ILGenerator myIL = myMethodBuilder.GetILGenerator();
myIL.EmitWriteLine("Hello, world!");//在HelloWorld方法中，创建一行等效于Console.Write("Hello,world!");的代码
myIL.Emit(OpCodes.Ret);//HelloWorld方法的return语句
return myTypeBuilder.CreateType();
}
}
/// <summary>
/// 创建一个自定义的Attribute，稍后将它应用在动态创建的“类型”上
/// </summary>
public class ClassCreatorAttribute : Attribute
{
private string creator;
public string Creator
{
get
{
return creator;
}
}
public ClassCreatorAttribute(string name)
{
this.creator = name;
}
}
/// <summary>
/// 创建一个自定义的Attribute，稍后将它应用在动态创建的“方法”上
/// </summary>
public class DateLastUpdatedAttribute : Attribute
{
private string dateUpdated;
public string DateUpdated
{
get
{
return dateUpdated;
}
}
public DateLastUpdatedAttribute(string theDate)
{
this.dateUpdated = theDate;
}
}
}
运行输出结果：
Custom Attributes for Type 'MyType':
-- Attribute: [CustomAttributeBuilderSample.ClassCreatorAttribute = "Joe Program mer"]
Custom Attributes for Method 'HelloWorld()' in 'MyType':
-- Attribute: [CustomAttributeBuilderSample.DateLastUpdatedAttribute = "2011/11/ 13 21:46:31"]
---
Hello, world!