假设我们需要一个名叫Kitty的类，其在Pets程序集下。
1 // specify a new assembly name
2 var assemblyName = new AssemblyName("Pets");
3
4 // create assembly builder
5 var assemblyBuilder = AppDomain.CurrentDomain
6 .DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);
7
8 // create module builder
9 var moduleBuilder = assemblyBuilder.DefineDynamicModule("PetsModule", "Pets.dll");
10
11 // create type builder for a class
12 var typeBuilder = moduleBuilder.DefineType("Kitty", TypeAttributes.Public);
定义字段
Kitty类包含两个私有字段_id和_name。用类型构造器来定义，
1 var fieldId = typeBuilder.DefineField( 2 "_id", typeof(int), FieldAttributes.Private); 3 var fieldName = typeBuilder.DefineField( 4 "_name", typeof(string), FieldAttributes.Private);
定义构造函数
Kitty类包含一个有两个参数的构造函数，参数一为整型id，参数而为字符串型name。构造函数内，将参数id赋值给私有字段_id，将参数name赋值给私有字段_name，
1 Type objType = Type.GetType("System.Object");
2 ConstructorInfo objCtor = objType.GetConstructor(new Type[0]);
3
4 Type[] constructorArgs = { typeof(int), typeof(string) };
5
6 var constructorBuilder = typeBuilder.DefineConstructor(
7 MethodAttributes.Public, CallingConventions.Standard, constructorArgs);
8 ILGenerator ilOfCtor = constructorBuilder.GetILGenerator();
9
10 ilOfCtor.Emit(OpCodes.Ldarg_0);
11 ilOfCtor.Emit(OpCodes.Call, objCtor);
12 ilOfCtor.Emit(OpCodes.Ldarg_0);
13 ilOfCtor.Emit(OpCodes.Ldarg_1);
14 ilOfCtor.Emit(OpCodes.Stfld, fieldId);
15 ilOfCtor.Emit(OpCodes.Ldarg_0);
16 ilOfCtor.Emit(OpCodes.Ldarg_2);
17 ilOfCtor.Emit(OpCodes.Stfld, fieldName);
18 ilOfCtor.Emit(OpCodes.Ret);
定义属性
为Kitty类创建Id和Name两个属性，读取和设置私有字段_id和_name。C#中的属性定义的getter和setter分别为两个方法。
1 var methodGetId = typeBuilder.DefineMethod(
2 "GetId", MethodAttributes.Public, typeof(int), null);
3 var methodSetId = typeBuilder.DefineMethod(
4 "SetId", MethodAttributes.Public, null, new Type[] { typeof(int) });
5
6 var ilOfGetId = methodGetId.GetILGenerator();
7 ilOfGetId.Emit(OpCodes.Ldarg_0); // this
8 ilOfGetId.Emit(OpCodes.Ldfld, fieldId);
9 ilOfGetId.Emit(OpCodes.Ret);
10
11 var ilOfSetId = methodSetId.GetILGenerator();
12 ilOfSetId.Emit(OpCodes.Ldarg_0); // this
13 ilOfSetId.Emit(OpCodes.Ldarg_1); // the first one in arguments list
14 ilOfSetId.Emit(OpCodes.Stfld, fieldId);
15 ilOfSetId.Emit(OpCodes.Ret);
16
17 // create Id property
18 var propertyId = typeBuilder.DefineProperty(
19 "Id", PropertyAttributes.None, typeof(int), null);
20 propertyId.SetGetMethod(methodGetId);
21 propertyId.SetSetMethod(methodSetId);
22
23 var methodGetName = typeBuilder.DefineMethod(
24 "GetName", MethodAttributes.Public, typeof(string), null);
25 var methodSetName = typeBuilder.DefineMethod(
26 "SetName", MethodAttributes.Public, null, new Type[] { typeof(string) });
27
28 var ilOfGetName = methodGetName.GetILGenerator();
29 ilOfGetName.Emit(OpCodes.Ldarg_0); // this
30 ilOfGetName.Emit(OpCodes.Ldfld, fieldName);
31 ilOfGetName.Emit(OpCodes.Ret);
32
33 var ilOfSetName = methodSetName.GetILGenerator();
34 ilOfSetName.Emit(OpCodes.Ldarg_0); // this
35 ilOfSetName.Emit(OpCodes.Ldarg_1); // the first one in arguments list
36 ilOfSetName.Emit(OpCodes.Stfld, fieldName);
37 ilOfSetName.Emit(OpCodes.Ret);
38
39 // create Name property
40 var propertyName = typeBuilder.DefineProperty(
41 "Name", PropertyAttributes.None, typeof(string), null);
42 propertyName.SetGetMethod(methodGetName);
43 propertyName.SetSetMethod(methodSetName);
定义方法
为Kitty类增加一个ToString()方法，返回一个字符串值。
1 // create ToString() method
2 var methodToString = typeBuilder.DefineMethod(
3 "ToString",
4 MethodAttributes.Virtual | MethodAttributes.Public,
5 typeof(string),
6 null);
7
8 var ilOfToString = methodToString.GetILGenerator();
9 var local = ilOfToString.DeclareLocal(typeof(string)); // create a local variable
10 ilOfToString.Emit(OpCodes.Ldstr, "Id:[{0}], Name:[{1}]");
11 ilOfToString.Emit(OpCodes.Ldarg_0); // this
12 ilOfToString.Emit(OpCodes.Ldfld, fieldId);
13 ilOfToString.Emit(OpCodes.Box, typeof(int)); // boxing the value type to object
14 ilOfToString.Emit(OpCodes.Ldarg_0); // this
15 ilOfToString.Emit(OpCodes.Ldfld, fieldName);
16 ilOfToString.Emit(OpCodes.Call,
17 typeof(string).GetMethod("Format",
18 new Type[] { typeof(string), typeof(object), typeof(object) }));
19 ilOfToString.Emit(OpCodes.Stloc, local); // set local variable
20 ilOfToString.Emit(OpCodes.Ldloc, local); // load local variable to stack
21 ilOfToString.Emit(OpCodes.Ret);
保存类型
生成类型，并保存程序集至Pets.dll文件。
1 // then create the whole class type
2 var classType = typeBuilder.CreateType();
3
4 // save assembly
5 assemblyBuilder.Save("Pets.dll");
反编译类
使用反编译器来查看生成的类，
1 using System;
2 public class Kitty
3 {
4 private int _id;
5 private string _name;
6 public int Id
7 {
8 get
9 {
10 return this._id;
11 }
12 set
13 {
14 this._id = value;
15 }
16 }
17 public string Name
18 {
19 get
20 {
21 return this._name;
22 }
23 set
24 {
25 this._name = value;
26 }
27 }
28 public Kitty(int id, string name)
29 {
30 this._id = id;
31 this._name = name;
32 }
33 public override string ToString()
34 {
35 return string.Format("Id:[{0}], Name:[{1}]", this._id, this._name);
36 }
37 }
完整代码
1 using System;
2 using System.Reflection;
3 using System.Reflection.Emit;
4
5 namespace EmitCreateMembers
6 {
7 class Program
8 {
9 static void Main(string[] args)
10 {
11 // specify a new assembly name
12 var assemblyName = new AssemblyName("Pets");
13
14 // create assembly builder
15 var assemblyBuilder = AppDomain.CurrentDomain
16 .DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);
17
18 // create module builder
19 var moduleBuilder = assemblyBuilder.DefineDynamicModule("PetsModule", "Pets.dll");
20
21 // create type builder for a class
22 var typeBuilder = moduleBuilder.DefineType("Kitty", TypeAttributes.Public);
23
24 // then create whole class structure
25 CreateKittyClassStructure(typeBuilder);
26
27 // then create the whole class type
28 var classType = typeBuilder.CreateType();
29
30 // save assembly
31 assemblyBuilder.Save("Pets.dll");
32
33 Console.WriteLine("Hi, Dennis, a Pets assembly has been generated for you.");
34 Console.ReadLine();
35 }
36
37 private static void CreateKittyClassStructure(TypeBuilder typeBuilder)
38 {
39 // ---- define fields ----
40
41 var fieldId = typeBuilder.DefineField(
42 "_id", typeof(int), FieldAttributes.Private);
43 var fieldName = typeBuilder.DefineField(
44 "_name", typeof(string), FieldAttributes.Private);
45
46 // ---- define costructors ----
47
48 Type objType = Type.GetType("System.Object");
49 ConstructorInfo objCtor = objType.GetConstructor(new Type[0]);
50
51 Type[] constructorArgs = { typeof(int), typeof(string) };
52
53 var constructorBuilder = typeBuilder.DefineConstructor(
54 MethodAttributes.Public, CallingConventions.Standard, constructorArgs);
55 ILGenerator ilOfCtor = constructorBuilder.GetILGenerator();
56
57 ilOfCtor.Emit(OpCodes.Ldarg_0);
58 ilOfCtor.Emit(OpCodes.Call, objCtor);
59 ilOfCtor.Emit(OpCodes.Ldarg_0);
60 ilOfCtor.Emit(OpCodes.Ldarg_1);
61 ilOfCtor.Emit(OpCodes.Stfld, fieldId);
62 ilOfCtor.Emit(OpCodes.Ldarg_0);
63 ilOfCtor.Emit(OpCodes.Ldarg_2);
64 ilOfCtor.Emit(OpCodes.Stfld, fieldName);
65 ilOfCtor.Emit(OpCodes.Ret);
66
67 // ---- define properties ----
68
69 var methodGetId = typeBuilder.DefineMethod(
70 "GetId", MethodAttributes.Public, typeof(int), null);
71 var methodSetId = typeBuilder.DefineMethod(
72 "SetId", MethodAttributes.Public, null, new Type[] { typeof(int) });
73
74 var ilOfGetId = methodGetId.GetILGenerator();
75 ilOfGetId.Emit(OpCodes.Ldarg_0); // this
76 ilOfGetId.Emit(OpCodes.Ldfld, fieldId);
77 ilOfGetId.Emit(OpCodes.Ret);
78
79 var ilOfSetId = methodSetId.GetILGenerator();
80 ilOfSetId.Emit(OpCodes.Ldarg_0); // this
81 ilOfSetId.Emit(OpCodes.Ldarg_1); // the first one in arguments list
82 ilOfSetId.Emit(OpCodes.Stfld, fieldId);
83 ilOfSetId.Emit(OpCodes.Ret);
84
85 // create Id property
86 var propertyId = typeBuilder.DefineProperty(
87 "Id", PropertyAttributes.None, typeof(int), null);
88 propertyId.SetGetMethod(methodGetId);
89 propertyId.SetSetMethod(methodSetId);
90
91 var methodGetName = typeBuilder.DefineMethod(
92 "GetName", MethodAttributes.Public, typeof(string), null);
93 var methodSetName = typeBuilder.DefineMethod(
94 "SetName", MethodAttributes.Public, null, new Type[] { typeof(string) });
95
96 var ilOfGetName = methodGetName.GetILGenerator();
97 ilOfGetName.Emit(OpCodes.Ldarg_0); // this
98 ilOfGetName.Emit(OpCodes.Ldfld, fieldName);
99 ilOfGetName.Emit(OpCodes.Ret);
100
101 var ilOfSetName = methodSetName.GetILGenerator();
102 ilOfSetName.Emit(OpCodes.Ldarg_0); // this
103 ilOfSetName.Emit(OpCodes.Ldarg_1); // the first one in arguments list
104 ilOfSetName.Emit(OpCodes.Stfld, fieldName);
105 ilOfSetName.Emit(OpCodes.Ret);
106
107 // create Name property
108 var propertyName = typeBuilder.DefineProperty(
109 "Name", PropertyAttributes.None, typeof(string), null);
110 propertyName.SetGetMethod(methodGetName);
111 propertyName.SetSetMethod(methodSetName);
112
113 // ---- define methods ----
114
115 // create ToString() method
116 var methodToString = typeBuilder.DefineMethod(
117 "ToString",
118 MethodAttributes.Virtual | MethodAttributes.Public,
119 typeof(string),
120 null);
121
122 var ilOfToString = methodToString.GetILGenerator();
123 var local = ilOfToString.DeclareLocal(typeof(string)); // create a local variable
124 ilOfToString.Emit(OpCodes.Ldstr, "Id:[{0}], Name:[{1}]");
125 ilOfToString.Emit(OpCodes.Ldarg_0); // this
126 ilOfToString.Emit(OpCodes.Ldfld, fieldId);
127 ilOfToString.Emit(OpCodes.Box, typeof(int)); // boxing the value type to object
128 ilOfToString.Emit(OpCodes.Ldarg_0); // this
129 ilOfToString.Emit(OpCodes.Ldfld, fieldName);
130 ilOfToString.Emit(OpCodes.Call,
131 typeof(string).GetMethod("Format",
132 new Type[] { typeof(string), typeof(object), typeof(object) }));
133 ilOfToString.Emit(OpCodes.Stloc, local); // set local variable
134 ilOfToString.Emit(OpCodes.Ldloc, local); // load local variable to stack
135 ilOfToString.Emit(OpCodes.Ret);
136 }
137 }
138 }