使用Ajax BeginForm提交，控制器接收UsersDetails参数为null的问题

问题原因 #

你的Razor视图绑定的是SettingViewModel，表单字段的name属性会自动生成为UsersDetails.username、UsersDetails.kullaniciAd这种带前缀的格式。而控制器接收的是UsersDetails类型参数，ASP.NET模型绑定器无法将带UsersDetails前缀的字段值映射到UsersDetails对象的属性上，导致参数为null。

解决方案 #

方案1：修改表单字段的name属性 #

在Html.TextBoxFor中手动指定name属性，去掉UsersDetails前缀，让字段名和UsersDetails的属性名直接匹配：

@model GAP_Bakim.ViewModel.SettingViewModel

@using (Ajax.BeginForm("Details", "Setting", new AjaxOptions { HttpMethod = "POST", OnSuccess = "detailSuccess", OnFailure = "detailFailure" }))
{
    @Html.AntiForgeryToken()

    <div class="input-box mb-3">
        <span>Kullanıcı Adı</span>
        @Html.TextBoxFor(m => m.UsersDetails.username, new { @class = "form-control details-inputs", id = "detailUsernameInput", required = "required", @readonly = "readonly", name = "username" })
    </div>

    <div class="input-box mb-3">
        <span>Ad</span>
        @Html.TextBoxFor(m => m.UsersDetails.kullaniciAd, new { @class = "form-control details-inputs", id = "detailNameInput", required = "required", maxlength = 25, pattern = "[A-Za-zğüşıöçĞÜŞİÖÇ\u0020]+", name = "kullaniciAd" })
    </div>
}

方案2：在控制器参数上添加绑定前缀特性 #

在控制器的UsersDetails参数上添加[Bind(Prefix = "UsersDetails")]，告诉模型绑定器字段的前缀是UsersDetails，实现正确映射：

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Details([Bind(Prefix = "UsersDetails")] UsersDetails users)
{
    // 业务逻辑处理
}

方案3：手动从请求中取值（不推荐） #

如果前两种方法不适用，可手动从Request.Form中获取字段值并构造UsersDetails对象：

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Details()
{
    var users = new UsersDetails
    {
        username = Request.Form["UsersDetails.username"],
        kullaniciAd = Request.Form["UsersDetails.kullaniciAd"]
    };
    // 业务逻辑处理
}

内容的提问来源于stack exchange，提问作者krautcez