为什么不能将表单数据直接绑定到操作方法参数？

Question

I have action method like that:

public ActionResult Index(HttpPostedFileBase image, int variable)

and form element like that:

variable 1:<input type="text" name="variable" value="1234" />

when I start debugging I am getting following exception:

The parameters dictionary contains a null entry for parameter 'variable' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Index(System.Web.HttpPostedFileBase, Int32)' in 'Stream.Controllers.HomeController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

what is wrong with this?

Answer 1

Try this:

public ActionResult Index(HttpPostedFileBase image, int? variable)

The question mark ( ? ) indicates that variable is a nullable variable and then it can be assigned the null value.

To know more about nullable types, read this on MSDN: Nullable Types (C# Programming Guide)

Answer 2

Try:

<input type="text" id="variable" name="variable" value="1234" />

Give an ID and see if you get the same issue... also, I know you probably know this, but to verify, you did put it within the form being posted, correct?

Answer 3

确保您的<input>在<form>标记中，并且该表单是正在执行其操作的表单。