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 class12 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); // this13 ilOfSetId.Emit(OpCodes.Ldarg_1); // the first one in arguments list14 ilOfSetId.Emit(OpCodes.Stfld, fieldId);15 ilOfSetId.Emit(OpCodes.Ret);16 17 // create Id property18 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); // this30 ilOfGetName.Emit(OpCodes.Ldfld, fieldName);31 ilOfGetName.Emit(OpCodes.Ret);32 33 var ilOfSetName = methodSetName.GetILGenerator();34 ilOfSetName.Emit(OpCodes.Ldarg_0); // this35 ilOfSetName.Emit(OpCodes.Ldarg_1); // the first one in arguments list36 ilOfSetName.Emit(OpCodes.Stfld, fieldName);37 ilOfSetName.Emit(OpCodes.Ret);38 39 // create Name property40 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 variable10 ilOfToString.Emit(OpCodes.Ldstr, "Id:[{0}], Name:[{1}]");11 ilOfToString.Emit(OpCodes.Ldarg_0); // this12 ilOfToString.Emit(OpCodes.Ldfld, fieldId);13 ilOfToString.Emit(OpCodes.Box, typeof(int)); // boxing the value type to object14 ilOfToString.Emit(OpCodes.Ldarg_0); // this15 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 variable20 ilOfToString.Emit(OpCodes.Ldloc, local); // load local variable to stack21 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 type2 var classType = typeBuilder.CreateType();3 4 // save assembly5 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 set13 {14 this._id = value;15 }16 }17 public string Name18 {19 get20 {21 return this._name;22 }23 set24 {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); // this103 ilOfSetName.Emit(OpCodes.Ldarg_1); // the first one in arguments list104 ilOfSetName.Emit(OpCodes.Stfld, fieldName);105 ilOfSetName.Emit(OpCodes.Ret);106 107 // create Name property108 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() method116 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 variable124 ilOfToString.Emit(OpCodes.Ldstr, "Id:[{0}], Name:[{1}]");125 ilOfToString.Emit(OpCodes.Ldarg_0); // this126 ilOfToString.Emit(OpCodes.Ldfld, fieldId);127 ilOfToString.Emit(OpCodes.Box, typeof(int)); // boxing the value type to object128 ilOfToString.Emit(OpCodes.Ldarg_0); // this129 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 variable134 ilOfToString.Emit(OpCodes.Ldloc, local); // load local variable to stack135 ilOfToString.Emit(OpCodes.Ret);136 }137 }138 }