iot/projects/Infrastructure/Extensions/ViewDataDictionaryExtensions.cs

using System;
using System.Linq.Expressions;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;

namespace Infrastructure.Extensions
{
    public static class ViewDataDictionaryExtensions
    {
        public static void SelectList<TResult>(this ViewDataDictionary viewData, string name, SelectList selectList)
        {
            viewData[name + "SelectList"] = selectList;
        }

        public static void SelectList<TResult>(this ViewDataDictionary viewData, Expression<Func<object, TResult>> expression, Func<SelectList> getSelectListFunc, bool value = true)
        {
            if (value)
            {
                var name = (expression.Body as MemberExpression).Member.Name + "SelectList";
                viewData[name] = getSelectListFunc();
            }
        }

        public static void MultiSelectList<TResult>(this ViewDataDictionary viewData, Expression<Func<object, TResult>> expression, Func<MultiSelectList> getSelectListFunc, bool value = true)
        {
            if (value)
            {
                var name = (expression.Body as MemberExpression).Member.Name + "SelectList";
                if (!viewData.ContainsKey(name))
                {
                    viewData[name] = getSelectListFunc();
                }
            }
        }
    }
}