将 ViewModel 值传递给按钮或 ActionLink 单击上的 MVC 控制器操作方法

Question

我有一个 asp.net/razor 页面，其中有几个下拉菜单，我尝试创建一个按钮或操作链接，在 "AccountController" class 并将下拉列表中选择的值传递给该方法。我一直在尝试各种方法，但 none 中的方法非常有效：

    @model SpecSelRepos.Models.AccountViewModels.ManageRolesViewModel

    <fieldset>
        <label for="selectUserName">Users:</label>
        <select asp-for="ManageRolesUser" asp-items="Model.Users"></select>
        &nbsp;
        <label for="selectRoleName">Roles:</label>
        <select asp-for="ManageRolesRole" asp-items="Model.Roles"></select>
        &nbsp;

        @*button 1*@
        @using (Html.BeginForm("AssignRole", "Account"))
        {
            <input type="submit" value="Add User to Role" name="buttonAddUserToRole">


         }

        @*button 2*@
        <button class="btn btn-info" type="button" name="assignRole" onclick="location.href='@Url.Action("AssignRole", "Account", new { email = Model.ManageRolesUser, role = Model.ManageRolesRole })'"></button>

        @*link 1*@
        @Html.ActionLink("Assign Role", "AssignRole", "Account", new { email = Model.ManageRolesUser, role = Model.ManageRolesRole }, null)

        @*link 2*@
        @Html.ActionLink("Assign Role", "AssignRole", "Account", new { email = Model.ManageRolesUser, role = Model.ManageRolesRole })

    </fieldset>

在 class AccountController 中，我有以下操作方法：

public async Task<IActionResult> AssignRole(string email, string role)
        {
            ApplicationUser user = GetUserByEmail(email);
            if(null == user)
            {
                return Content("No user with given email:" + email);
            }
            // if the role exists, assign the role to the user
            if (await _roleManager.RoleExistsAsync(role))
            {
                if(!await _userManager.IsInRoleAsync(user, role))
                {
                    await _userManager.AddToRoleAsync(user, role);
                    return Content("Role assigned: " + GetUserRoles(user));
                }
                else
                {
                    return Content ("User is in role: " + role + ": " + GetUserRoles(user));
                }
            }
            else
            {
                return Content("Role: " + role + " does not exist");
            }
        }

点击按钮1无明显效果。按钮 2 和两个链接似乎都调用了 AssignRole 方法，但所有 3 个都抛出空值错误：

ArgumentNullException: Value cannot be null.
 Parameter name: email
Microsoft.AspNetCore.Identity.UserManager.FindByEmailAsync(string email)
SpecSelRepos.Controllers.AccountController.GetUserByEmail(string email) in AccountController.cs
+                return _userManager.FindByEmailAsync(email).Result;
SpecSelRepos.Controllers.AccountController+<AssignRole>d__10.MoveNext() in AccountController.cs
+                ApplicationUser user = GetUserByEmail(email);

因此，该方法似乎已按需调用，但视图模型中的值作为空值传递，而不是在下拉框中选择的值。

这是视图模型class:

public class ManageRolesViewModel
    {
        private readonly UserManager<ApplicationUser> _userManager;

        public ManageRolesViewModel(UserManager<ApplicationUser> userManager, RoleManager<IdentityRole> roleManager)
        {
            _userManager = userManager;
            Users = new SelectList(userManager.Users.ToList());
            Roles = new SelectList(roleManager.Roles.ToList());
        }

        public SelectList Users;
        public SelectList Roles;
        public string ManageRolesUser { get; set; }//contains the specific user the user selects
        public string ManageRolesRole { get; set; }//contains the specific role the user selects

        public List<ApplicationUser> GetUsersInRole(string role)
        {
            var users = _userManager.GetUsersInRoleAsync(role).Result.ToList();
            return users;
        }
    }

一些帮助将不胜感激。

Answer 1

将您的视图更改为如下所示，我使用了带有表单方法和操作的表单，这将确保表单内的任何输入都序列化为与它们同名的参数

@model WebApplication3.Models.ManageRolesViewModel

<fieldset>
    @using (Html.BeginForm("AssignRole", "Account", FormMethod.Get))
    {
        <span>
            <label for="email">Users:</label>
            @Html.DropDownList("email", @Model.Users)
        </span>
        <span>
            <label for="role">Roles:</label>
            @Html.DropDownList("role", @Model.Roles)
        </span>

        <input class="btn btn-info" type="submit" name="assignRole"/>
    }

</fieldset>

由于 "email" 和 "role" 匹配控制器签名中的参数，因此将传递所选 ID（不是文本值）

当然，前提是您传递给视图的 selectList 已填充 "dataValueField" 和 "dataTextField"。

我还（不一定需要）将您的 AssignRoles 方法归因于： [HttpGet]

但这只是为了冗长。我坚持一致性:)

将 ViewModel 值传递给按钮或 ActionLink 单击上的 MVC 控制器操作方法

Passing ViewModel values to MVC Controller action method on button or ActionLink click

c#

asp.net

asp.net-mvc

controller

razor-pages