C# Emit ，如何编写 if 语句

首先，我有课

    internal class Parent
    {
        protected void Write(string message, [CallerMemberName] string caller = null)
        {
            Console.WriteLine($"{caller} :: {message}");
        }
    }

我想动态创建一个类，该类有一个属性“Name”，如果属性值更改则调用 write 方法，看起来像

    class Child : Parent
    {
        private string _name;

        public string Name
        {
            get { return _name; }
            set
            {

                if (_name != value)
                {
                    Write("changedto: " + value);
                    _name = value;
                }

            }
        }
    }

我想知道的是突出显示条款。 怎么写在emit里呢？ 请帮忙。

我想要下面的一些代码

     private static MethodBuilder BuildSetter(TypeBuilder typeBuilder, PropertyInfo property, FieldBuilder fieldBuilder, MethodAttributes attributes)
    {
        var setterBuilder = typeBuilder.DefineMethod($"set_{property.Name}", attributes, null, new Type[] { property.PropertyType });
        var ilGenerator = setterBuilder.GetILGenerator();

        ilGenerator.Emit(OpCodes.Ldarg_0);  //this
        ilGenerator.Emit(OpCodes.Ldarg_1);  // the first one in arguments list

            //code should be here

        ilGenerator.Emit(OpCodes.Stfld, fieldBuilder);
        ilGenerator.Emit(OpCodes.Ret);

        return setterBuilder;
    }

Updated

var typeBuilder = moduleBuilder.DefineType(typeName, TypeAttributes.Public,typeof(PropertyChanged));


var t = typeof(PropertyChanged);

var m2 = t.GetMethod("ValueChanged");

你看，当我创建类型时，我使用父类型，并且在父类型中有一个名为“ValueChanged”的方法

protected void ValueChanged(object value,[CallerMemberName] string property = null)

我想在 set 方法中调用它。

update 2

private static MethodBuilder BuildSetter(TypeBuilder typeBuilder, PropertyInfo property, FieldBuilder fieldBuilder, MethodAttributes attributes)
{
    var propertyType = property.PropertyType;
    var setterBuilder = typeBuilder.DefineMethod($"set_{property.Name}", attributes, null, new Type[] { propertyType });

    var setIl = setterBuilder.GetILGenerator();
    Label exitSet = setIl.DefineLabel(); // define label to jump in case condition is false
    setIl.Emit(OpCodes.Ldarg_0); // this
    setIl.Emit(OpCodes.Ldfld, fieldBuilder); // _name field
    setIl.Emit(OpCodes.Ldarg_1); // value

    var inequality = propertyType.GetMethod("Equals", new[] { propertyType});
    setIl.Emit(OpCodes.Callvirt, inequality); // '!=' method
    setIl.Emit(OpCodes.Brtrue_S, exitSet); // check for inequality


    setIl.Emit(OpCodes.Ldarg_0); // load string literal
    setIl.Emit(OpCodes.Ldarg_1); // value
    setIl.Emit(OpCodes.Ldstr, property.Name);

    var m = typeBuilder.BaseType.GetMethod("ValueChanged", new Type[] {typeof(object),typeof(string) });

    setIl.Emit(OpCodes.Call, m);

    setIl.Emit(OpCodes.Ldarg_0); // this
    setIl.Emit(OpCodes.Ldarg_1); // value
    setIl.Emit(OpCodes.Stfld, fieldBuilder); // save the new value into _name
    setIl.MarkLabel(exitSet); // mark the label
    setIl.Emit(OpCodes.Ret); // return

    return setterBuilder;
}

update 3 screen-snaps

update 4

maybe , i have found the error reason , see Reflection Emit and Type Inheritance: Calling Base Type Constructors https://softwareproduction.eu/2014/07/21/reflection-emit-and-type-inheritance-calling-base-type-constructors/

update 5

最后，我得到了错误原因。这不是我在更新4时猜测的，它是由调用父方法“ValueChanged”引起的。在我们将参数传递给方法之前，我们应该Box如果原始数据类型是，则它作为对象值类型。请参阅下面的参考资料，

C# 发出，类型值比较 https://stackoverflow.com/questions/54686465/c-sharp-emit-type-value-compare/54687187#54687187

@AlbertK 答案向您展示了正确的方法，我将添加完整的代码。希望它会有所帮助。

我将所有内容都放在一种方法中......按照您的意愿重构它。

// define assembly and module
var propertyName = "Name";
var propertyType = typeof(string);
var ab = AssemblyBuilder.DefineDynamicAssembly(
            new AssemblyName("dynamicAssembly"), 
            AssemblyBuilderAccess.Save);
var mb = ab.DefineDynamicModule("dynamicModule", "dynamicModule.dll");

// define type, field and property
var tb = mb.DefineType("dynamicType");
var fb = tb.DefineField("_name", propertyType, FieldAttributes.Private);
var pb = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, Type.EmptyTypes);
var get = tb.DefineMethod("get_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);
var set = tb.DefineMethod("set_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, null, new[] { propertyType });

// write the IL for the get method
var getIl = get.GetILGenerator();
getIl.Emit(OpCodes.Ldarg_0); // this
getIl.Emit(OpCodes.Ldfld, fb); // _name field
getIl.Emit(OpCodes.Ret);

// write the IL for the set method
var setIl = set.GetILGenerator();
Label exitSet = setIl.DefineLabel(); // define label to jump in case condition is false
setIl.Emit(OpCodes.Ldarg_0); // this
setIl.Emit(OpCodes.Ldfld, fb); // _name field
setIl.Emit(OpCodes.Ldarg_1); // value
var inequality = propertyType.GetMethod("op_Inequality", new[] { propertyType, propertyType });
setIl.Emit(OpCodes.Call, inequality); // '!=' method
setIl.Emit(OpCodes.Brfalse_S, exitSet); // check for inequality
setIl.Emit(OpCodes.Ldstr, "changedto:"); // load string literal
setIl.Emit(OpCodes.Ldarg_1); // value
var concat = propertyType.GetMethod("Concat", new[] { propertyType, propertyType });
setIl.Emit(OpCodes.Call, concat); // concat two strings (literal + value)
var writeline = typeof(Console).GetMethod("WriteLine", new[] { propertyType });
setIl.Emit(OpCodes.Call, writeline); // write
setIl.Emit(OpCodes.Ldarg_0); // this
setIl.Emit(OpCodes.Ldarg_1); // value
setIl.Emit(OpCodes.Stfld, fb); // save the new value into _name
setIl.MarkLabel(exitSet); // mark the label
setIl.Emit(OpCodes.Ret); // return
pb.SetGetMethod(get);
pb.SetSetMethod(set);

tb.CreateType(); // complete the type
ab.Save("dynamicModule.dll"); // save the assembly to disk

结果

internal class dynamicType
{
    private string _name;

    public string Name
    {
        get
        {
            return this._name;
        }
        set
        {
            if (this._name != value)
            {
                 Console.WriteLine("changedto:" + value);
                 this._name = value;
            }
        }
    }
}