如何定义带有一个模块的动态程序集

下面的代码示例演示如何定义带有一个模块的动态程序集。 该示例程序集中的模块包含一个类型 MyDynamicType，该类型具有私有字段、获取和设置私有字段的属性、初始化私有字段的构造函数，以及将用户提供的数与私有字段值相乘并返回结果的方法。

创建程序集时指定 AssemblyBuilderAccess.RunAndSave。 程序集代码可立即使用，并且程序集将保存到磁盘，以便可以使用 Ildasm.exe（MSIL 反汇编程序） 对其进行检查或将其用于另一个程序。

using System;
using System.Reflection;
using System.Reflection.Emit;

class DemoAssemblyBuilder
{
public static void Main()
{
// An assembly consists of one or more modules, each of which
// contains zero or more types. This code creates a single-module
// assembly, the most common case. The module contains one type,
// named "MyDynamicType", that has a private field, a property
// that gets and sets the private field, constructors that
// initialize the private field, and a method that multiplies
// a user-supplied number by the private field value and returns
// the result. In C# the type might look like this:
/*
public class MyDynamicType
{
private int m_number;

public MyDynamicType() : this(42) {}
public MyDynamicType(int initNumber)
{
m_number = initNumber;
}

public int Number
{
get { return m_number; }
set { m_number = value; }
}

public int MyMethod(int multiplier)
{
return m_number * multiplier;
}
}
*/

AssemblyName aName = new AssemblyName("DynamicAssemblyExample");
AssemblyBuilder ab =
AppDomain.CurrentDomain.DefineDynamicAssembly(
aName,
AssemblyBuilderAccess.RunAndSave);

// For a single-module assembly, the module name is usually
// the assembly name plus an extension.
ModuleBuilder mb =
ab.DefineDynamicModule(aName.Name, aName.Name + ".dll");

TypeBuilder tb = mb.DefineType(
"MyDynamicType",
TypeAttributes.Public);

// Add a private field of type int (Int32).
FieldBuilder fbNumber = tb.DefineField(
"m_number",
typeof(int),
FieldAttributes.Private);

// Define a constructor that takes an integer argument and
// stores it in the private field.
Type[] parameterTypes = { typeof(int) };
ConstructorBuilder ctor1 = tb.DefineConstructor(
MethodAttributes.Public,
CallingConventions.Standard,
parameterTypes);

ILGenerator ctor1IL = ctor1.GetILGenerator();
// For a constructor, argument zero is a reference to the new
// instance. Push it on the stack before calling the base
// class constructor. Specify the default constructor of the
// base class (System.Object) by passing an empty array of
// types (Type.EmptyTypes) to GetConstructor.
ctor1IL.Emit(OpCodes.Ldarg_0);
ctor1IL.Emit(OpCodes.Call,
typeof(object).GetConstructor(Type.EmptyTypes));
// Push the instance on the stack before pushing the argument
// that is to be assigned to the private field m_number.
ctor1IL.Emit(OpCodes.Ldarg_0);
ctor1IL.Emit(OpCodes.Ldarg_1);
ctor1IL.Emit(OpCodes.Stfld, fbNumber);
ctor1IL.Emit(OpCodes.Ret);

// Define a default constructor that supplies a default value
// for the private field. For parameter types, pass the empty
// array of types or pass null.
ConstructorBuilder ctor0 = tb.DefineConstructor(
MethodAttributes.Public,
CallingConventions.Standard,
Type.EmptyTypes);

ILGenerator ctor0IL = ctor0.GetILGenerator();
// For a constructor, argument zero is a reference to the new
// instance. Push it on the stack before pushing the default
// value on the stack, then call constructor ctor1.
ctor0IL.Emit(OpCodes.Ldarg_0);
ctor0IL.Emit(OpCodes.Ldc_I4_S, 42);
ctor0IL.Emit(OpCodes.Call, ctor1);
ctor0IL.Emit(OpCodes.Ret);

// Define a property named Number that gets and sets the private
// field.
//
// The last argument of DefineProperty is null, because the
// property has no parameters. (If you don't specify null, you must
// specify an array of Type objects. For a parameterless property,
// use the built-in array with no elements: Type.EmptyTypes)
PropertyBuilder pbNumber = tb.DefineProperty(
"Number",
PropertyAttributes.HasDefault,
typeof(int),
null);

// The property "set" and property "get" methods require a special
// set of attributes.
MethodAttributes getSetAttr = MethodAttributes.Public |
MethodAttributes.SpecialName | MethodAttributes.HideBySig;

// Define the "get" accessor method for Number. The method returns
// an integer and has no arguments. (Note that null could be
// used instead of Types.EmptyTypes)
MethodBuilder mbNumberGetAccessor = tb.DefineMethod(
"get_Number",
getSetAttr,
typeof(int),
Type.EmptyTypes);

ILGenerator numberGetIL = mbNumberGetAccessor.GetILGenerator();
// For an instance property, argument zero is the instance. Load the
// instance, then load the private field and return, leaving the
// field value on the stack.
numberGetIL.Emit(OpCodes.Ldarg_0);
numberGetIL.Emit(OpCodes.Ldfld, fbNumber);
numberGetIL.Emit(OpCodes.Ret);

// Define the "set" accessor method for Number, which has no return
// type and takes one argument of type int (Int32).
MethodBuilder mbNumberSetAccessor = tb.DefineMethod(
"set_Number",
getSetAttr,
null,
new Type[] { typeof(int) });

ILGenerator numberSetIL = mbNumberSetAccessor.GetILGenerator();
// Load the instance and then the numeric argument, then store the
// argument in the field.
numberSetIL.Emit(OpCodes.Ldarg_0);
numberSetIL.Emit(OpCodes.Ldarg_1);
numberSetIL.Emit(OpCodes.Stfld, fbNumber);
numberSetIL.Emit(OpCodes.Ret);

// Last, map the "get" and "set" accessor methods to the
// PropertyBuilder. The property is now complete.
pbNumber.SetGetMethod(mbNumberGetAccessor);
pbNumber.SetSetMethod(mbNumberSetAccessor);

// Define a method that accepts an integer argument and returns
// the product of that integer and the private field m_number. This
// time, the array of parameter types is created on the fly.
MethodBuilder meth = tb.DefineMethod(
"MyMethod",
MethodAttributes.Public,
typeof(int),
new Type[] { typeof(int) });

ILGenerator methIL = meth.GetILGenerator();
// To retrieve the private instance field, load the instance it
// belongs to (argument zero). After loading the field, load the
// argument one and then multiply. Return from the method with
// the return value (the product of the two numbers) on the
// execution stack.
methIL.Emit(OpCodes.Ldarg_0);
methIL.Emit(OpCodes.Ldfld, fbNumber);
methIL.Emit(OpCodes.Ldarg_1);
methIL.Emit(OpCodes.Mul);
methIL.Emit(OpCodes.Ret);

// Finish the type.
Type t = tb.CreateType();

// The following line saves the single-module assembly. This
// requires AssemblyBuilderAccess to include Save. You can now
// type "ildasm MyDynamicAsm.dll" at the command prompt, and
// examine the assembly. You can also write a program that has
// a reference to the assembly, and use the MyDynamicType type.
//
ab.Save(aName.Name + ".dll");

// Because AssemblyBuilderAccess includes Run, the code can be
// executed immediately. Start by getting reflection objects for
// the method and the property.
MethodInfo mi = t.GetMethod("MyMethod");
PropertyInfo pi = t.GetProperty("Number");

// Create an instance of MyDynamicType using the default
// constructor.
object o1 = Activator.CreateInstance(t);

// Display the value of the property, then change it to 127 and
// display it again. Use null to indicate that the property
// has no index.
Console.WriteLine("o1.Number: {0}", pi.GetValue(o1, null));
pi.SetValue(o1, 127, null);
Console.WriteLine("o1.Number: {0}", pi.GetValue(o1, null));

// Call MyMethod, passing 22, and display the return value, 22
// times 127. Arguments must be passed as an array, even when
// there is only one.
object[] arguments = { 22 };
Console.WriteLine("o1.MyMethod(22): {0}",
mi.Invoke(o1, arguments));

// Create an instance of MyDynamicType using the constructor
// that specifies m_Number. The constructor is identified by
// matching the types in the argument array. In this case,
// the argument array is created on the fly. Display the
// property value.
object o2 = Activator.CreateInstance(t,
new object[] { 5280 });
Console.WriteLine("o2.Number: {0}", pi.GetValue(o2, null));
}
}

/* This code produces the following output:

o1.Number: 42
o1.Number: 127
o1.MyMethod(22): 2794
o2.Number: 5280
*/

生成的DynamicAssemblyExample.dll，经过反编译后，代码如下：

using System;

public class MyDynamicType
{
private int m_number;

public MyDynamicType() : this(0x2a)
{
}

public MyDynamicType(int num1)
{
this.m_number = num1;
}

public int MyMethod(int num1)
{
return (this.m_number * num1);
}

public int Number
{
get
{
return this.m_number;
}
set
{
this.m_number = value;
}
}
}

参考：http://msdn.microsoft.com/zh-cn/library/system.reflection.emit.assemblybuilder.aspx