GreenTree.Strohrmann.ERP/GreenTree.Strohrmann.ERP.Web/Extension/ViewDataExtension.cs

using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Threading.Tasks;

namespace GreenTree.Strohrmann.ERP.Web.Extension
{
    public static class ViewDataExtension
    {
        /// <summary>
        /// Adds a predefined selection item list in the ViewData dictionary used by many HtmlContent input methods
        /// </summary>
        /// <typeparam name="TValue">The list base value type.</typeparam>
        /// <param name="viewDataDict">The ViewData dictionary.</param>
        /// <param name="key">The ViewData key.</param>
        /// <param name="source">The base data source.</param>
        /// <param name="valueExpression">The expression for the value.</param>
        /// <param name="textExpression">The expression for the display text.</param>
        /// <param name="selectedValue">The value of the optional pre selected item.</param>
        public static void AddSelectList<TValue>(this ViewDataDictionary viewDataDict,
            string key, IEnumerable<TValue> source, Func<TValue, object> valueExpression, Func<TValue, object> textExpression,
            object selectedValue = null)
        {
            if (viewDataDict == null) return;

            if (String.IsNullOrEmpty(key)) return;

            if (source == null)
                throw new ArgumentNullException("source", "The specified data source must not be NULL.");

            var selectItemList = new List<SelectListItem>();

            foreach (var item in source)
            {
                var val = valueExpression(item).ToString();
                var text = textExpression(item).ToString();

                if (selectedValue != null && val == selectedValue.ToString())
                    selectItemList.Add(new SelectListItem(text, val, true));
                else
                    selectItemList.Add(new SelectListItem(text, val));
            }

            viewDataDict.Add(key, selectItemList);
        }
    }
}