C# 如何使用 Reflection.Emit 调用带有谓词的 LINQ 的第一个方法

Question

im trying to wrap my head around Reflection.Emit, im playing around with it to understand how it works.

im trying to implement this method:

public static object GetTableKeyValue(object tableValue) => tableValue.GetType().GetProperties().First(property => property.GetCustomAttribute<KeyAttribute>() is not null).GetValue(tableValue);

This is what i did so far:

public static object GetTableKeyValueReflectionEmit(object val)
        {
            var getTableKeyValue = new DynamicMethod("GetTableKeyValueReflectionEmit", typeof(object), new Type[] { typeof(object) }, typeof(object).Module);
            getTableKeyValue.DefineParameter(1, ParameterAttributes.In, "tableValue");
            var il = getTableKeyValue.GetILGenerator(256);

            il.Emit(OpCodes.Ldarg_0);
            il.EmitCall(OpCodes.Call, typeof(object).GetMethod(nameof(object.GetType)), null);
            il.EmitCall(OpCodes.Call, typeof(Type).GetMethod(nameof(Type.GetProperties), new Type[] { }), null);
            Func<PropertyInfo, bool> predicate = property => (!property.GetCustomAttribute<KeyAttribute>().Equals(null));
            // im stuck here
            il.EmitCall(OpCodes.Call, typeof(Enumerable).GetMember(nameof(Enumerable.First)).OfType<MethodInfo>().First(method => method.GetParameters().Length == 1), new Type[] { typeof(Func<PropertyInfo, bool>) });
            il.EmitCall(OpCodes.Call, typeof(PropertyInfo).GetMethod(nameof(PropertyInfo.GetValue), new Type[] { typeof(object) }), new Type[] { typeof(object) });

            il.Emit(OpCodes.Ret);

            var getTableKeyValueDelegate = (GetTableKeyValueDelegate)getTableKeyValue.CreateDelegate(typeof(GetTableKeyValueDelegate));
            return getTableKeyValueDelegate(val);
        }

i cant understand how to define a predicate of type Func<PropertyInfo, bool> and pass it to the First method, and i cant really find good information on Reflection.Emit, i guess its not that common to do it.

Help would be appreciated.

Answer 1

This seems to be working for me:

public static object GetTableKeyValueReflectionEmit(object val) {
    var getTableKeyValue = new DynamicMethod("GetTableKeyValueReflectionEmit", typeof(object), new Type[] { typeof(object) }, typeof(object).Module);
    getTableKeyValue.DefineParameter(1, ParameterAttributes.In, "tableValue");
    var il = getTableKeyValue.GetILGenerator(256);

    il.Emit(OpCodes.Ldarg_0);
    il.EmitCall(OpCodes.Call, typeof(object).GetMethod(nameof(object.GetType)), null);
    il.EmitCall(OpCodes.Call, typeof(Type).GetMethod(nameof(Type.GetProperties), new Type[] { }), null);
    Func<PropertyInfo, bool> predicate = property => (!property.GetCustomAttribute<KeyAttribute>().Equals(null));
    il.Emit(OpCodes.Ldftn, predicate.GetMethodInfo());
    var miFirstGeneric = typeof(Enumerable).GetMember(nameof(Enumerable.First)).OfType<MethodInfo>().First(method => method.GetParameters().Length == 1);
    var miFirst = miFirstGeneric.MakeGenericMethod(typeof(PropertyInfo));
    il.Emit(OpCodes.Call, miFirst);
    il.Emit(OpCodes.Call, typeof(PropertyInfo).GetMethod(nameof(PropertyInfo.GetValue), new Type[] { typeof(object) }));

    il.Emit(OpCodes.Ret);

    var getTableKeyValueDelegate = (GetTableKeyValueDelegate)getTableKeyValue.CreateDelegate(typeof(GetTableKeyValueDelegate));
    return getTableKeyValueDelegate(val);
}