意外的模型绑定

Question

通过带有个人帐户身份验证的脚手架 MVC 5 模板，我偶然发现了一种我无法理解的行为。

给定一个请求 url

http://localhost:53487/Account/ResetPassword?userId=4&code=T634Hfv%2BxMAlo2XjdLV6a%2Bd1%2BxGsfdiQiKRW0Nh2fB3I1U3S%2BNdXU4ixHC9uJ5F5PSRMZkQgV907CDH0x3aQPSdFliXJqD7nrjk3TLnOTawPeO8CJjk5OEyYijVur1i1Fr7DE7nmaDD93I000fXbQA%3D%3D

AccountController中的动作方法

[AllowAnonymous]
public ActionResult ResetPassword(string code)
{
    return code == null ? View("Error") : View();
}

和视图ResetPassword.cshtml

@model OPLA.Web.Models.ResetPasswordViewModel
@{
    ViewBag.Title = "Reset password";
}

<h2>@ViewBag.Title.</h2>

@using (Html.BeginForm("ResetPassword", "Account", FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
    @Html.AntiForgeryToken()
    <h4>Reset your password.</h4>
    <hr />
    @Html.ValidationSummary("", new { @class = "text-danger" })    
    @Html.HiddenFor(model => model.Code)
    <div class="form-group">
        @Html.LabelFor(m => m.Email, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.TextBoxFor(m => m.Email, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.Password, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.PasswordFor(m => m.Password, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        @Html.LabelFor(m => m.ConfirmPassword, new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.PasswordFor(m => m.ConfirmPassword, new { @class = "form-control" })
        </div>
    </div>
    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" class="btn btn-default" value="Reset" />
        </div>
    </div>
}

和视图模型ResetPasswordViewModel

public class ResetPasswordViewModel
{
    [Required]
    [EmailAddress]
    [Display(Name = "Email")]
    public string Email { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [DataType(DataType.Password)]
    [Display(Name = "Confirm password")]
    [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }

    public string Code { get; set; }
}

加载视图时，@Html.HiddenFor(model => model.Code) 行会生成此 html 输出，其中视图模型的 Code 属性已正确填充/绑定：

<input id="Code" name="Code" type="hidden" value="T634Hfv+xMAlo2XjdLV6a+d1+xGsfdiQiKRW0Nh2fB3I1U3S+NdXU4ixHC9uJ5F5PSRMZkQgV907CDH0x3aQPSdFliXJqD7nrjk3TLnOTawPeO8CJjk5OEyYijVur1i1Fr7DE7nmaDD93I000fXbQA==">

模型绑定器是如何知道code查询字符串参数属于viewmodel的Code属性并自动绑定的？

Answer 1

您的方法中有一个名为code 的参数。当方法执行时，code 的值被添加到ModelState。

您的模型还有一个名为Code 的属性。您的视图使用@Html.HiddenFor() 为该属性生成<input>。所有生成表单控件的HtmlHelper 方法（PasswordFor() 除外）通过按以下顺序读取值来确定<input> 的value

1. ModelState
2. ViewDataDictionary
3. 房产的实际价值

因为ModelState 包含code 的值（不区分大小写），所以value 是从方法参数（即查询字符串值）中设置的。

有关为什么这种行为是设计使然的更详细说明，请参阅TextBoxFor displaying initial value, not the value updated from code 的第二部分。