我编写了一个帮助方法，在我的asp.net MVC应用程序中显示我模型中的枚举，作为我视图中的下拉列表。
这是我的代码：
public static List<SelectListItem> CreateSelectItemList<TEnum>(object enumObj,
string defaultItemKey,
bool sortAlphabetically,
object firstValueOverride)
where TEnum : struct
{
var values = (from v in (TEnum[])Enum.GetValues(typeof(TEnum))
select new
{
Id = Convert.ToInt32(v),
Name = ResourceHelpers.GetResourceValue(AppConstants.EnumResourceNamespace,
typeof(TEnum).Name, v.ToString())
});
return values.ToSelectList(e => e.Name,
e => e.Id.ToString(),
!string.IsNullOrEmpty(defaultItemKey) ? ResourceHelpers.GetResourceValue(AppConstants.EnumResourceNamespace, defaultItemKey) : string.Empty,
enumObj,
sortAlphabetically,
firstValueOverride);
}
这实际上会生成选择项目列表：
public static List<SelectListItem> ToSelectList<T>(
this IEnumerable<T> enumerable,
Func<T, string> text,
Func<T, string> value,
string defaultOption,
object selectedVal,
bool sortAlphabetically,
object FirstValueOverride)
{
int iSelectedVal = -1;
if(selectedVal!=null)
{
try
{
iSelectedVal = Convert.ToInt32(selectedVal);
}
catch
{
}
}
var items = enumerable.Select(f => new SelectListItem()
{
Text = text(f),
Value = value(f),
Selected = (iSelectedVal > -1)? (iSelectedVal.ToString().Equals(value(f))) : false
});
#region Sortare alfabetica
if (sortAlphabetically)
items = items.OrderBy(t => t.Text);
#endregion Sortare alfabetica
var itemsList = items.ToList();
Func<SelectListItem, bool> funct = null;
string sValue = string.Empty;
SelectListItem firstItem = null;
SelectListItem overridenItem = null;
int overridenIndex = 0;
if (FirstValueOverride != null)
{
sValue = FirstValueOverride.ToString();
funct = (t => t.Value == sValue);
overridenItem = itemsList.SingleOrDefault(funct);
overridenIndex = itemsList.IndexOf(overridenItem);
if (overridenItem != null)
{
firstItem = itemsList.ElementAt(0);
itemsList[0] = overridenItem;
itemsList[overridenIndex] = firstItem;
}
}
if(!string.IsNullOrEmpty(defaultOption))
itemsList.Insert(0, new SelectListItem()
{
Text = defaultOption,
Value = "-1"
});
return itemsList;
}
这是我称之为的方法：
public static MvcHtmlString EnumDropDownList<TEnum>(this HtmlHelper htmlHelper,
object enumObj,
string name,
string defaultItemKey,
bool sortAlphabetically,
object firstValueOverride,
object htmlAttributes)
where TEnum : struct
{
return htmlHelper.DropDownList(name,
CreateSelectItemList<TEnum>(enumObj,
defaultItemKey,
sortAlphabetically,
firstValueOverride),
htmlAttributes);
}
现在我遇到了here所描述的问题
当我调用这个辅助方法并且输入的名称与属性的名称相同时，选择的值不会被选中。
那里描述的替代解决方案对我不起作用。唯一有效的解决方案是更改名称，而不是使用FormCollection使用模型绑定。
我不喜欢这种解决方法，因为我不能再使用ViewModel模式进行验证，我必须为每个枚举编写一些额外的代码。
我尝试编写一个自定义模型绑定器以某种方式对此进行补偿，但是当我开始操作时，没有一个我可以覆盖的方法被调用。
有没有办法在不使用FormCollection的情况下执行此操作？ 我可以以某种方式拦截ASP.NET MVC，当它试图将值放入我的输入字段并使其选择正确的值时？
提前谢谢。
答案 0 :(得分：0)
我现在有一个解决方案 以下是EnumDropDownList函数的代码，其他函数列在问题中：
public static MvcHtmlString EnumDropDownList(this HtmlHelper htmlHelper,
object enumObj,
string name,
string defaultItemKey,
bool sortAlphabetically,
object firstValueOverride,
object htmlAttributes)
{
StringBuilder sbRezultat = new StringBuilder();
int selectedIndex = 0;
var selectItemList = new List<SelectListItem>();
if (enumObj != null)
{
selectItemList = CreateSelectItemList(enumObj, defaultItemKey, true, null);
var selectedItem = selectItemList.SingleOrDefault(item => item.Selected);
if (selectedItem != null)
{
selectedIndex = selectItemList.IndexOf(selectedItem);
}
}
var dict = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);
TagBuilder tagBuilder = new TagBuilder("select");
tagBuilder.MergeAttribute("name", name,true);
bool bReadOnly = false;
//special case for readonly
if(dict.ContainsKey("readonly"))
{
//remove this tag it won't work the way mvc renders it anyway
dict.Remove("readonly");
bReadOnly = true;
}
//in case the style element is completed if the drop down is not readonly
tagBuilder.MergeAttributes(dict, true);
if (bReadOnly)
{
//add a small javascript to make it readonly and add the lightgrey style
tagBuilder.MergeAttribute("onchange", "this.selectedIndex=" + selectedIndex + ";",true);
tagBuilder.MergeAttribute("style", "background: lightgrey", true);
}
sbRezultat.Append(tagBuilder.ToString(TagRenderMode.StartTag));
foreach (var option in selectItemList)
{
sbRezultat.Append(" <option value='");
sbRezultat.Append(option.Value);
sbRezultat.Append("' ");
if (option.Selected)
sbRezultat.Append("selected");
sbRezultat.Append(" >");
sbRezultat.Append(option.Text);
sbRezultat.Append("</option>");
}
sbRezultat.Append("</select>");
return new MvcHtmlString(sbRezultat.ToString());
}
我还写了For（EnumDropDownFor）类型的泛型函数：
public static MvcHtmlString EnumDropDownListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
Expression<Func<TModel, TProperty>> expression,
string defaultItemKey,
bool sortAlphabetically,
object firstValueOverride,
object htmlAttributes)
where TProperty : struct
{
string inputName = GetInputName(expression);
object selectedVal = null;
try
{
selectedVal = htmlHelper.ViewData.Model == null
? default(TProperty)
: expression.Compile()(htmlHelper.ViewData.Model);
}
catch//in caz ca e ceva null sau ceva de genu'
{
}
return EnumDropDownList(htmlHelper,
selectedVal,
inputName,
defaultItemKey,
sortAlphabetically,
firstValueOverride,
htmlAttributes);
}
和一些辅助方法：
public static string GetInputName<TModel, TProperty>(Expression<Func<TModel, TProperty>> expression)
{
if (expression.Body.NodeType == ExpressionType.Call)
{
MethodCallExpression methodCallExpression = (MethodCallExpression)expression.Body;
string name = GetInputName(methodCallExpression);
return name.Substring(expression.Parameters[0].Name.Length + 1);
}
return expression.Body.ToString().Substring(expression.Parameters[0].Name.Length + 1);
}
private static string GetInputName(MethodCallExpression expression)
{
MethodCallExpression methodCallExpression = expression.Object as MethodCallExpression;
if (methodCallExpression != null)
{
return GetInputName(methodCallExpression);
}
return expression.Object.ToString();
}