在下拉列表中選擇的MVC4驗證項目

Question

我有一個頁面來創建objects ，並且在其中有一個DropDownList 。 如果我從列表中選擇一個項目，我的頁面將正確保存，但是，如果我不選擇一個項目，則它似乎在回發時失敗，因為對象將為null。

我想要的是嘗試驗證用戶是否已選擇一個項目（默認為“請選擇...”）。

我有將檢查並在控制器中查看該項目是否為空的代碼，但是這又如何顯示一條消息？ 保留所有其他詳細信息（如果存在）。

public ActionResult Create(int objectId = 0)
{
var resultModel = new MyObjectModel();
resultModel.AllObjects = new SelectList(_system.GetAllObjects(objectId)); 
// GetAllObjects juts returns a list of items for the drop down.
return View(resultModel);
}

[HttpPost]
public ActionResult Create(int? objectId, FormCollection collection)
{
try
{
int objectIdNotNull = 0;
if (objectId > 1)
{
objectIdNotNull = (int) objectId;
}
string objectName = collection["Name"];
int objectTypeSelectedResult = 1;
int.TryParse(collection["dllList"], out objectTypeSelectedResult);
if (!Convert.ToBoolean(objectTypeSelectedResult))
{
// So here I have discovered nothing has been selected, and I want to alert the user
    return RedirectToAction("Create",
        new {ObjectId = objectIdNotNull, error = "Please select an Object Type"});
}
....

return RedirectToAction(...)

}
catch
{
return View();
}
}

上面的代碼僅進入“創建”頁面，但未顯示錯誤。 在創建視圖中，我假設以下行將顯示任何錯誤：@ViewData [“ error”]

附加代碼模型：

using System.Collections.Generic;
using System.Web.Mvc;
using System.ComponentModel.DataAnnotations;

namespace MyNameSpace
{
public class MyObjectModel
{
[Required(ErrorMessage = "Please select an Object Type")]
public SelectList AllObjects { get; set; }  // I populate the drop down with this list
}
}

視圖：

@model MyNameSpace.MyObjectModel

@{
ViewBag.Title = "Create";
}

<h2>Create </h2>

<p class="text-error">@ViewData["Message"]</p>

<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"> </script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"> </script>

@using (Html.BeginForm())
{ 
@Html.ValidationSummary(true)
<fieldset>       
<div class="editor-label">
@Html.LabelFor(model => model.MyObject.Name)
</div>
<div class="editor-field">
@Html.TextBoxFor(model=>model.MyObjectType.Name, new {style="width: 750px"})
@Html.ValidationMessageFor(model => model.MyObjectType.Name)
</div>

<div>
<label for="ddlList">Choose Type</label>
@if (@Model != null)
{  
@Html.DropDownList("ddlList", Model.AllObjects, "Please Select...")
@Html.ValidationMessageFor(model => model.AllObjects, "An object must be selected", new { @class = "redText"})
}
</div>

<p>
<input type="submit" value="Create" />
</p>
</fieldset>
}

Answer 1

您正在驗證錯誤的SelectList

[必需（ErrorMessage =“必須選擇一個對象”）
公共SelectList AllObjects {get; 組; }

您的模型應該是

[Required(ErrorMessage = "Please select an Object Type")]
public int ObjectId { get; set; }
public string ObjectName { get; set; }

您的控制器（不需要表單收集，這就是MVC的重點）

public ActionResult Create(int Id = 0)
{
    MyObjectModel resultModel = new MyObjectModel();

    var ObjectResultList = _system.GetAllObjects(Id);
    var ObjectSelectList = new SelectList(ObjectResultList, "id", "Name");
    ViewBag.ObjectList = ObjectSelectList;

    return View(resultModel);
}

您的Post控制器：

[HttpPost]
public ActionResult Create(MyObjectModel o)
{
    try
    {
            if (ModelState.IsValid)
            {
                            //It's valid , your code here!

                return RedirectToAction("ObjectCreated", new { id = o.objectId });
            }
            else
            {
                var errors = ModelState
                    .Where(x => x.Value.Errors.Count > 0)
                    .Select(x => new { x.Key, x.Value.Errors })
                    .ToArray();
            }
        }
    }
    catch (Exception ex)
    {
        Response.Write(ex.InnerException.Message);
    }
    //If we get here it means the model is not valid, We're in trouble
    //then redisplay the view repopulate the dropdown
    var ObjectResultList = _system.GetAllObjects(objectId);
    var ObjectSelectList = new SelectList(ObjectResultList, "id", "value");
    ViewBag.ObjectList = ObjectSelectList;


    return View(o);
}

您的視圖應為強類型

<div class="editor-label">
    @Html.LabelFor(model => model.ObjectId)
</div>
<div class="editor-field">
    @Html.DropDownListFor(model => model.ObjectId,
       (IEnumerable<SelectListItem>)ViewBag.ObjectList, "-- Select One Object --")
    @Html.ValidationMessageFor(model => model.ObjectId)
</div>