动态创建类和方法(一)

.net提供了在运行期动态创建类型的机制。Spring.net 中应用其中的实现来实现AOPProxy.

对于类，需要制定Assembly, Module, Class Name以及类中的成员。

对MSDN上面的代码解释一下：

首先制定需要创建类型的Assembly和Module

        AssemblyBuilder myAsmBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(
                                         new AssemblyName("Banks.APP"), 
                                         AssemblyBuilderAccess.RunAndSave);
        ModuleBuilder pointModule = myAsmBuilder.DefineDynamicModule("Banks.APP", "1234.dll");

通过使用ModuleBuilder创建TypeBuilder

TypeBuilder matrixTypeBld = pointModule.DefineType("Matrix", TypeAttributes.Public);

创建成员字段

        FieldBuilder xField = matrixTypeBld.DefineField("x", typeof(int),
                                                           FieldAttributes.Public);
        FieldBuilder yField = matrixTypeBld.DefineField("y", typeof(int),
                                                           FieldAttributes.Public);
        FieldBuilder zField = matrixTypeBld.DefineField("z", typeof(int),
                                                           FieldAttributes.Public);

 

 

创建ConstructorBuilder

ConstructorBuilder pointCtor = matrixTypeBld.DefineConstructor(
                   MethodAttributes.Public,
                   CallingConventions.Standard,
                   ctorParams);
ILGenerator ctorIL = pointCtor.GetILGenerator();

将以下代码以IL代码的形式写入

this.x = x;
this.y = y;
this.z = z;

实际IL代码类似如下:

  IL_0000:  ldarg.0
  IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
  IL_0006:  nop
  IL_0007:  nop
  IL_0008:  ldarg.0
  IL_0009:  ldarg.1
  IL_000a:  stfld      int32 Matrix::x
  IL_000f:  ldarg.0
  IL_0010:  ldarg.2
  IL_0011:  stfld      int32 Matrix::y
  IL_0016:  ldarg.0
  IL_0017:  ldarg.3
  IL_0018:  stfld      int32 Matrix::z
  IL_001d:  nop
  IL_001e:  ret

实际代码:

        ctorIL.Emit(OpCodes.Ldarg_0);

        Type objType = typeof(Object);
        ConstructorInfo objCtor = objType.GetConstructor(new Type[0]);

        // Here, we wish to create an instance of System.Object by invoking its
        // constructor, as specified above.

        ctorIL.Emit(OpCodes.Call, objCtor);

        // Now, we'll load the current instance ref in arg 0, along
        // with the value of parameter "x" stored in arg 1, into stfld.

        ctorIL.Emit(OpCodes.Ldarg_0);
        ctorIL.Emit(OpCodes.Ldarg_1);
        ctorIL.Emit(OpCodes.Stfld, xField);

        // Now, we store arg 2 "y" in the current instance with stfld.

        ctorIL.Emit(OpCodes.Ldarg_0);
        ctorIL.Emit(OpCodes.Ldarg_2);
        ctorIL.Emit(OpCodes.Stfld, yField);

        // Last of all, arg 3 "z" gets stored in the current instance.

        ctorIL.Emit(OpCodes.Ldarg_0);
        ctorIL.Emit(OpCodes.Ldarg_3);
        ctorIL.Emit(OpCodes.Stfld, zField);

        // Our work complete, we return.

        ctorIL.Emit(OpCodes.Ret);

通过对比真实的IL代码，ldarg_0实际上就是获得this的引用，MSDN中没有详细解释arg_0，只是说明:Load argument 0 onto stack

arg_1, arg_2, arg_3是实际构造函数的三个参数，将其各自赋值到三个类成员变量x,y,z中。