Razor 語法@Html.DropDownList，根據List集合或者枚舉生成Select標簽

1、根據List集合生成Select標簽，根據數據庫數據換成SelectListItem集合

Action 方法（也可使用下方的List集合的擴展方法）：

var selectList = DBList.Select(f => new SelectListItem { Value = f.Key, Text = f.Value }).ToList();
selectList.Insert(0, new SelectListItem() { Value = "-1", Text = "請選擇" });
ViewData["selectList"] = selectList;

 

View視圖：

@Html.DropDownListFor(m => m.HandleBy, ViewData["selectList"] as IEnumerable<SelectListItem>, new { @class = "form-control selectWidth" })

 

2、根據枚舉擴展方法生成Select標簽

View視圖：

@Html.DropDownList("ContractStyle", new Model.Enums.ContractStyleType().ToSelectList(), "全部", new { @class = "form-control" })

 

擴展方法：

    public static class SelectListExtension
    {
        public static IEnumerable<SelectListItem> CreateRangeSelect(int nimNumber, int maxNumber, string formatter = null)
        {
            for (int i = nimNumber; i <= maxNumber; i++)
                yield return new SelectListItem { Value = i.ToString(formatter), Text = i.ToString(formatter) };
        }

        public static IEnumerable<SelectListItem> ToSelectListItem(this Dictionary<int, string> items, string defaultValue = null)
        {
            if (!string.IsNullOrWhiteSpace(defaultValue))
                yield return new SelectListItem { Value = "", Text = defaultValue };

            foreach (var item in items)
                yield return new SelectListItem { Value = item.Key.ToString(), Text = item.Value };
        }

        public static SelectList ToSelectList<TEnum>(this TEnum enumObj)
            where TEnum : struct, IComparable, IFormattable, IConvertible
        {
            var values = from TEnum e in Enum.GetValues(typeof(TEnum))
                         select new { Id = Convert.ToInt32(e), Name = GetEnumDescription(e) };
            return new SelectList(values, "Id", "Name");
        }

        /// <summary>將枚舉類型轉化為SelectListItem列表
        /// </summary>
        /// <typeparam name="TEnum"></typeparam>
        /// <param name="enumObject">The enum object.</param>
        /// <param name="firstItemText">The first item text.</param>
        /// <param name="selectedId">The selected identifier.</param>
        /// <returns></returns>
        public static List<SelectListItem> EnumToSelectListItems<TEnum>(string firstItemText = null, int selectedId = -1)
        {
            var selectList = new List<SelectListItem>();

            if (!string.IsNullOrEmpty(firstItemText))
            {
                selectList.Add(new SelectListItem()
                {
                    Value = "-1",
                    Text = firstItemText,
                    Selected = selectedId == -1
                });
            }
            selectList.AddRange(from TEnum e in Enum.GetValues(typeof(TEnum))
                                select new SelectListItem
                                {
                                    Value = Convert.ToInt32(e).ToString(),
                                    Text = GetEnumDescription(e),
                                    Selected = Convert.ToInt32(e) == selectedId
                                });

            return selectList;
        }
        public static List<SelectListItem> ToSelectListByFieldType<TEnum>(FieldTypeEnum? fieldType = null, string firstItemText = null, string firstItemValue = null, int selectedId = -1)
            where TEnum : struct, IComparable, IFormattable, IConvertible
        {
            var selectList = new List<SelectListItem>();

            if (!string.IsNullOrEmpty(firstItemText))
            {
                selectList.Add(new SelectListItem()
                {
                    Value = firstItemValue,
                    Text = firstItemText,
                    Selected = selectedId == -1
                });
            }
            if (fieldType.HasValue)//指定枚舉字段類型,只返回特定類型列表
            {
                foreach (TEnum e in Enum.GetValues(typeof(TEnum)))
                {
                    FieldInfo fi = e.GetType().GetField(e.ToString());
                    EnumValueFieldTypeAttribute[] fieldTypeAttributes = (EnumValueFieldTypeAttribute[])fi.GetCustomAttributes(typeof(EnumValueFieldTypeAttribute), false);
                    if (fieldTypeAttributes == null || fieldTypeAttributes.Length == 0 || fieldTypeAttributes[0].FieldType != fieldType) continue;
                    var item = new SelectListItem
                    {
                        Value = Convert.ToInt32(e).ToString(),
                        Selected = Convert.ToInt32(e) == selectedId
                    };
                    DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
                    if ((attributes != null) && (attributes.Length > 0))
                        item.Text = attributes[0].Description;
                    else
                        item.Text = e.ToString();
                    selectList.Add(item);
                }
            }
            else//不指定枚舉字段類型，顯示全部
            {
                selectList.AddRange(from TEnum e in Enum.GetValues(typeof(TEnum))
                                    select new SelectListItem
                                    {
                                        Value = Convert.ToInt32(e).ToString(),
                                        Text = GetEnumDescription(e),
                                        Selected = Convert.ToInt32(e) == selectedId
                                    });
            }
            return selectList;
        }
        public static string GetEnumDescription<TEnum>(TEnum value)
        {
            FieldInfo fi = value.GetType().GetField(value.ToString());

            DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);

            if ((attributes != null) && (attributes.Length > 0))
                return attributes[0].Description;
            else
                return value.ToString();
        }

        /// <summary>將list轉換成SelectListItem列表
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="list">列表數據</param>
        /// <param name="firstItemText">第一個下拉框名稱（未空則不額外添加）</param>
        /// <param name="selectedId">已選項id</param>
        public static IEnumerable<SelectListItem> ListToSelectListItems<T>(this IEnumerable<T> list, string firstItemText, int selectedId = -1)
        {
            if (list == null)
            {
                return new List<SelectListItem>();
            }
            var t = typeof(T);
            List<SelectListItem> selectList = new List<SelectListItem>();
            if (!string.IsNullOrEmpty(firstItemText))
            {
                selectList.Add(new SelectListItem()
                {
                    Value = "-1",
                    Text = firstItemText,
                    Selected = selectedId == -1
                });
            }
            foreach (var item in list)
            {
                var addItem = new SelectListItem();
                foreach (var p in t.GetProperties())
                {
                    //id（約定為int類型）
                    if (p.PropertyType == typeof(System.Int32))
                    {
                        addItem.Value = p.GetValue(item).ToString();
                    }
                    else
                    {//value
                        addItem.Text = p.GetValue(item).ToString();
                    }
                    addItem.Selected = addItem.Value.Equals(selectedId);
                }
                selectList.Add(addItem);
            }
            return selectList;
        }


    }