Question

问题： 我有SubCategories类别列表，所以当我点击SubCategory项目时，它会将我重定向到条目列表。它在列表中有Create ActionLink。因此，当我单击SubCategoryItem创建ActionLink时，问题是传递SubCategoryId。如果没有CreateActionLink，它会列出条目，但是使用它，它会在索引视图中显示错误：

Object reference not set to an instance of an object.
Line 6:  
Line 7:  <p>
Line 8:      @Html.ActionLink("Create New", "Create", new { subCategoryId = @Model.SubCategoryId})
Line 9:  </p>
Line 10:

我明白我正在传递null引用，问题是如何避免这种情况？这是我的代码：

控制器：

public class EntryController : Controller
{
    public ActionResult Index()
    {        
        return View();
    }

    public ActionResult EntryList(int subCategoryId)
    {
        var entries = EntryDAL.GetEntries(subCategoryId);
        return View("_EntryList",entries);
    }

    public ActionResult Create(int subCategoryId)
    {
        var model = new Entry();

        model.SubCategoryId = subCategoryId;

        return View(model);
    }

    [HttpPost]
    public ActionResult Create(Entry entry)
    {
        try
        {
            if (ModelState.IsValid)
            {
                var add = EntryDAL.Add(entry);
                return RedirectToAction("Index");
            }

            return View(entry);
        }
        catch (Exception)
        {
            return View();
        }
    }

}

IndexView：

@model PasswordCloud.Domain.Models.SubCategory

@{
ViewBag.Title = "Index";
}

<p>
@Html.ActionLink("Create New", "Create", new { subCategoryId = @Model.SubCategoryId })
</p>

@{Html.RenderPartial("_EntryList",Model.EntryList);}

PartialView：

@model IEnumerable<PasswordCloud.Domain.Models.Entry>

<table>
<tr>
    <th>
        @Html.DisplayNameFor(model => model.Title)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Username)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Password)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Url)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.Description)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.SubCategoryId)
    </th>
    <th></th>
</tr>

@foreach (var item in Model) {
<tr>
    <td>
        @Html.DisplayFor(modelItem => item.Title)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Username)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Password)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Url)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.Description)
    </td>
    <td>
        @Html.DisplayFor(modelItem => item.SubCategoryId)
    </td>
    <td>
        @Html.ActionLink("Edit", "Edit", new { id=item.Id }) |
        @Html.ActionLink("Details", "Details", new { id=item.Id }) |
        @Html.ActionLink("Delete", "Delete", new { id=item.Id })
    </td>
</tr>
}

</table>

SubCategoryListItem查看：

@model IEnumerable<PasswordCloud.Domain.Models.SubCategory>

@foreach (var item in Model) {

@Html.ActionLink(item.Name,"Index","Entry", new { subCategoryId = item.SubCategoryId }, null)
}

Answer 1

在“索引”操作中，您永远不会创建模型并将其传递给视图。因此，当它到达您使用new { subCategoryId = @Model.SubCategoryId}的操作链接的行时，您的模型为空。因此，您将获得null ref异常。要修复它，你需要做这样的事情。

public ActionResult Index()
{        
    var model = ...
    return View(model);
}

如何将Id从一个视图传递到另一个MVC4

1 个答案: