MVC3视图中的模型计数检查

Question

Here is my view code:

@model IEnumerable<StudentRegistrationPortal.Models.CourseRegisterModel>
@{
    ViewBag.Title = "Welcome Student";
}

<h2>Welcome 
@Context.User.Identity.Name
</h2>
@Html.ActionLink("[Sign Out]", "SignOut", "Student")
<ul>
    <li>@Html.ActionLink("Register Courses", "registerCourses", "Course")</li>
</ul>

<%if (Model.Count == 5) { %>
<table border="1">
<tr>
    <th>
        RollNumber
    </th>
    <th>
        Course Code
    </th>
    <th>
        Course Name
    </th>
    <th>Add/Drop</th>
</tr>

<tr>
    <td>
        @Context.User.Identity.Name
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(0).Course.Code)
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(0).Course.Name)
    </td>
    <td>
        @Html.ActionLink("Drop", "Drop", new { id=-1 })
    </td>
</tr>

<tr>
    <td>
        @Context.User.Identity.Name
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(1).Course.Code)
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(1).Course.Name)
    </td>
    <td>
        @Html.ActionLink("Drop", "Drop", new { id=-1 })
    </td>
</tr>

<tr>
    <td>
        @Context.User.Identity.Name
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(2).Course.Code)
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(2).Course.Name)
    </td>
    <td>
        @Html.ActionLink("Drop", "Drop", new { id=-1 })
    </td>
</tr>

<tr>
    <td>
        @Context.User.Identity.Name
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(3).Course.Code)
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(3).Course.Name)
    </td>
    <td>
        @Html.ActionLink("Drop", "Drop", new { id=-1 })
    </td>
</tr>

<tr>
    <td>
        @Context.User.Identity.Name
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(4).Course.Code)
    </td>
    <td>
        @Html.DisplayFor(modelItem => Model.ElementAt(4).Course.Name)
    </td>
    <td>
        @Html.ActionLink("Drop", "Drop", new { id=-1 })
    </td>
</tr>

</table>
<% } %>

I have added IF condition to only draw table if model count is equals to 5 but still if model contains no data then it gives error that:

Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

What is wrong with IF condition?

Thanks.

Answer 1

your code will only work if you have exactly 5 CourseRegisterModel . This is your issue.

why don't you just iterate the model(s)

@foreach(StudentRegistrationPortal.Models.CourseRegisterModel modelValue in Model)
{
<tr>
    <td>
        @Context.User.Identity.Name
    </td>
    <td>
        @Html.DisplayFor(modelItem => modelValue.Course.Code)
    </td>
    <td>
        @Html.DisplayFor(modelItem => modelValue.Course.Name)
    </td>
    <td>
        @Html.ActionLink("Drop", "Drop", new { id=-1 })
    </td>
</tr>

}

Answer 2

if you really insist on doing this logic inside the view, then you can use operator precedence and check for the Model containing items. Without further addo, edit you line:

<%if (Model.Count == 5) { %>

to:

// check will only continue if Model.Any() evaluates to true
@if (Model.Any() && Model.Count == 5) { ... }

I would personally do this in my viewModel inside my service or controller class and really flesh out the logic required for this hardcoded Count == 5 existing. You aslo seem to be mixing razon and webforms syntax.

Answer 3

Why are you using <% syntax in if clause, change it to use @

 @if (Model.Count == 5) 
 {

also at the end change <% } %> to following

 }

Answer 4

If Model is Null then accessing to the count would be throw an exception. so before that you have to check that if the model is null or not.

@if(Mode != null && Mode.Count == 5)
{
//....