Model 列表属性为 NULL 发布在 controller

Question

So I have tested on a clean project an issue I've been getting, and have done the following code setup for checking if a custom Class object still returns null placed in a List:

VIEW

<div>
<div class="jumbotron">

    <h1 class="display-4"><span class="fas fa-user-secret"></span> Babcock Canada - Application Template</h1>
    <br />
    <div class="alert alert-primary" role="alert">
        <span class="fas fa-info-circle"></span>
        <span> This is the Babcock Canada MVC Application template for use in developing content-rich web applications.</span>
    </div>
    <hr class="my-4" />
</div>

<div>

    <div class="container-fluid">


        @if (!string.IsNullOrEmpty(Model.errorMessage))
        {
            <div class="alert alert-danger" role="alert">
                <span class="fas fa-stop-circle"></span> @Html.DisplayFor(alert => alert.errorMessage)
            </div>
        }
        @if (!string.IsNullOrEmpty(Model.successMessage))
        {
            <div class="alert alert-success" role="alert">
                <span class="fas fa-check-circle"></span> @Html.DisplayFor(alert => alert.successMessage)
            </div>
        }

        <div>
            @using (Html.BeginForm("TestAction", "Default", FormMethod.Post))
            {
                @Html.HiddenFor(m => Model.tester[0].tester)
                <button type="submit" class="btn btn-primary">
                    Submit 1
                </button>
            }
        </div>
        <div>
            @using (Html.BeginForm("TestAction", "Default", FormMethod.Post))
            {
                @Html.HiddenFor(m => Model.tester[1].tester)
                <button type="submit" class="btn btn-primary">
                    Submit 2
                </button>
            }
        </div>

    </div>
</div>

TestClass.cs

namespace Test.Models
{
    public class TestClass
    {
        public string tester { get; set; }
    }
}

MODEL

namespace Test.Models
{
/// <summary>
/// This is the default template model.
/// </summary>
public class DefaultModel : SharedModel
{
    public string errorMessage = string.Empty;
    public string successMessage = string.Empty;

    public List<TestClass> tester { get; set; }

    public DefaultModel()
    {

    }

    public void Init()
    {
        tester = new List<TestClass>
                 {
                     new TestClass { tester = "Testing..." },
                     new TestClass { tester = "Testing2..." }
                 };
    }
}
}

CONTROLLER

[HttpPost]
    public ActionResult TestAction(DefaultModel model)
    {
        return View(model);
    }

So the result is that the second one returns NULL in the list, but the first one returns just fine.

In my other project index 0 of a list looped in the same way returns the error: "An item with the same key has already been added."

So what am I doing wrong?

Answer 1

try using the helper Html.Hidden() instead

    <div>
        @using (Html.BeginForm("TestAction", "Default", FormMethod.Post))
        {
            @Html.Hidden("tester", Model.tester[0].tester)
            <button type="submit" class="btn btn-primary">
                Submit 1
            </button>
        }
    </div>
    <div>
        @using (Html.BeginForm("TestAction", "Default", FormMethod.Post))
        {
            @Html.Hidden("tester", Model.tester[1].tester)
            <button type="submit" class="btn btn-primary">
                Submit 2
            </button>
        }
    </div>

Answer 2

Turns out it doesn't work when the form is inside the loop, has to be outside and reference an ID value through the submit button holding the name "ID" and the value of that list item.

Suppose using Html.Hidden() would work, but that isn't what was required for the project.