Practical example of Dynamic method?

问题

I want to learn dynamic method and its practical example using c#.
Is there any relation between dynamic method and Reflection?
Please help me.

回答1:

We are using Dynamic methods for speed up Reflection. Here is code of our reflection optimizer. it is only 10% slower than direct call and 2000 times faster that reflection call

public class ReflectionEmitPropertyAccessor
    {
        private readonly bool canRead;
        private readonly bool canWrite;
        private IPropertyAccessor emittedPropertyAccessor;
        private readonly string propertyName;
        private readonly Type propertyType;
        private readonly Type targetType;
        private Dictionary<Type,OpCode> typeOpCodes;

        public ReflectionEmitPropertyAccessor(Type targetType, string property)
        {
            this.targetType = targetType;
            propertyName = property;
            var propertyInfo = targetType.GetProperty(property);
            if (propertyInfo == null)
            {
                throw new ReflectionOptimizerException(string.Format("Property \"{0}\" is not found in type "+ "{1}.", property, targetType));
            }
            canRead = propertyInfo.CanRead;
            canWrite = propertyInfo.CanWrite;
            propertyType = propertyInfo.PropertyType;
        }

        public bool CanRead
        {
            get { return canRead; }
        }

        public bool CanWrite
        {
            get { return canWrite; }
        }

        public Type TargetType
        {
            get { return targetType; }
        }

        public Type PropertyType
        {
            get { return propertyType; }
        }

        #region IPropertyAccessor Members

        public object Get(object target)
        {
            if (canRead)
            {
                if (emittedPropertyAccessor == null)
                {
                    Init();
                }

                if (emittedPropertyAccessor != null) return emittedPropertyAccessor.Get(target);

            }
            else
            {
                throw new ReflectionOptimizerException(string.Format("У свойства \"{0}\" нет метода get.", propertyName));
            }
            throw new ReflectionOptimizerException("Fail initialize of " + GetType().FullName);
        }

        public void Set(object target, object value)
        {
            if (canWrite)
            {
                if (emittedPropertyAccessor == null)
                {
                    Init();
                }
                if (emittedPropertyAccessor != null) emittedPropertyAccessor.Set(target, value);
            }
            else
            {
                throw new ReflectionOptimizerException(string.Format("Property \"{0}\" does not have method set.", propertyName));
            }
            throw new ReflectionOptimizerException("Fail initialize of " + GetType().FullName);
        }

        #endregion

        private void Init()
        {
            InitTypeOpCodes();
            var assembly = EmitAssembly();
            emittedPropertyAccessor = assembly.CreateInstance("Property") as IPropertyAccessor;
            if (emittedPropertyAccessor == null)
            {
                throw new ReflectionOptimizerException("Shit happense in PropertyAccessor.");
            }
        }

        private void InitTypeOpCodes()
        {
            typeOpCodes = new Dictionary<Type, OpCode>
                            {
                                {typeof (sbyte), OpCodes.Ldind_I1},
                                {typeof (byte), OpCodes.Ldind_U1},
                                {typeof (char), OpCodes.Ldind_U2},
                                {typeof (short), OpCodes.Ldind_I2},
                                {typeof (ushort), OpCodes.Ldind_U2},
                                {typeof (int), OpCodes.Ldind_I4},
                                {typeof (uint), OpCodes.Ldind_U4},
                                {typeof (long), OpCodes.Ldind_I8},
                                {typeof (ulong), OpCodes.Ldind_I8},
                                {typeof (bool), OpCodes.Ldind_I1},
                                {typeof (double), OpCodes.Ldind_R8},
                                {typeof (float), OpCodes.Ldind_R4}
                            };
        }

        private Assembly EmitAssembly()
        {
            var assemblyName = new AssemblyName {Name = "PropertyAccessorAssembly"};
            var newAssembly = Thread.GetDomain().DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
            var newModule = newAssembly.DefineDynamicModule("Module");
            var dynamicType = newModule.DefineType("Property", TypeAttributes.Public);
            dynamicType.AddInterfaceImplementation(typeof(IPropertyAccessor));
            dynamicType.DefineDefaultConstructor(MethodAttributes.Public);
            var getParamTypes = new[] { typeof(object) };
            var getReturnType = typeof(object);
            var getMethod = dynamicType.DefineMethod("Get",
                                    MethodAttributes.Public | MethodAttributes.Virtual,
                                    getReturnType,
                                    getParamTypes);

            var getIL = getMethod.GetILGenerator();
            var targetGetMethod = targetType.GetMethod("get_" + propertyName);

            if (targetGetMethod != null)
            {
                getIL.DeclareLocal(typeof(object));
                getIL.Emit(OpCodes.Ldarg_1); //Load the first argument 
                getIL.Emit(OpCodes.Castclass, targetType); //Cast to the source type
                getIL.EmitCall(OpCodes.Call, targetGetMethod, null); //Get the property value
                if (targetGetMethod.ReturnType.IsValueType)
                {
                    getIL.Emit(OpCodes.Box, targetGetMethod.ReturnType); //Box
                }
                getIL.Emit(OpCodes.Stloc_0); //Store it
                getIL.Emit(OpCodes.Ldloc_0);
            }
            else
            {
                getIL.ThrowException(typeof(MissingMethodException));
            }

            getIL.Emit(OpCodes.Ret);
            var setParamTypes = new[] { typeof(object), typeof(object) };
            const Type setReturnType = null;
            var setMethod = dynamicType.DefineMethod("Set",
                                    MethodAttributes.Public | MethodAttributes.Virtual,
                                    setReturnType,
                                    setParamTypes);

            var setIL = setMethod.GetILGenerator();

            var targetSetMethod = targetType.GetMethod("set_" + propertyName);
            if (targetSetMethod != null)
            {
                Type paramType = targetSetMethod.GetParameters()[0].ParameterType;

                setIL.DeclareLocal(paramType);
                setIL.Emit(OpCodes.Ldarg_1); //Load the first argument //(target object)
                setIL.Emit(OpCodes.Castclass, targetType); //Cast to the source type
                setIL.Emit(OpCodes.Ldarg_2); //Load the second argument 
                //(value object)
                if (paramType.IsValueType)
                {
                    setIL.Emit(OpCodes.Unbox, paramType); //Unbox it    
                    if (typeOpCodes.ContainsKey(paramType)) //and load
                    {
                        var load = typeOpCodes[paramType];
                        setIL.Emit(load);
                    }
                    else
                    {
                        setIL.Emit(OpCodes.Ldobj, paramType);
                    }
                }
                else
                {
                    setIL.Emit(OpCodes.Castclass, paramType); //Cast class
                }
                setIL.EmitCall(OpCodes.Callvirt,targetSetMethod, null); //Set the property value
            }
            else
            {
                setIL.ThrowException(typeof(MissingMethodException));
            }
            setIL.Emit(OpCodes.Ret);
            // Load the type
            dynamicType.CreateType();
            return newAssembly;
        }

    }

implementation is aggregated from different sources and main is this CodeProject article.

回答2:

You can create a method via DynamicMethod class.

DynamicMethod squareIt = new DynamicMethod(
    "SquareIt", 
    typeof(long), 
    methodArgs, 
    typeof(Example).Module);

ILGenerator il = squareIt.GetILGenerator();
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Conv_I8);
il.Emit(OpCodes.Dup);
il.Emit(OpCodes.Mul);
il.Emit(OpCodes.Ret);

Fully commented example on MSDN
I should note that the development using this method is very slow and not very useful.

来源：https://stackoverflow.com/questions/1960692/practical-example-of-dynamic-method