I have two forms: one for assigning roles to users and the other one for removing roles from users. They're strikingly similar, both the views and the controllers. Here they are (the form itself):
AssignRole.cshtml
@using (Html.BeginForm("AssignRole", "User", new { ReturnUrl = ViewBag.ReturnUrl }, FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
@Html.AntiForgeryToken()
@Html.ValidationSummary(true, "", new { @class = "text-danger" })
@Html.HiddenFor(m => m.UserID)
<div class="form-group">
@Html.LabelFor(m => m.UserName, new { @class = "col-md-2 control-label" })
<div class="col-md-10">
@Html.TextBoxFor(m => m.UserName, new { @class = "form-control", @readonly = "readonly" })
@Html.ValidationMessageFor(m => m.UserName, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
@Html.LabelFor(m => m.RoleName, new { @class = "col-md-2 control-label" })
<div class="col-md-10">
@Html.DropDownListFor(m => m.RoleName, new SelectList(Model.UnassignedRoles, "Value", "Text"), Resources.DropdownSelect, new { @class = "form-control" })
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="@Resources.Assign" class="btn btn-default" />
</div>
</div>
}
RemoveRole.cshtml
@using (Html.BeginForm("RemoveRole", "User", new { ReturnUrl = ViewBag.ReturnUrl }, FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
{
@Html.AntiForgeryToken()
@Html.ValidationSummary(true, "", new { @class = "text-danger" })
@Html.HiddenFor(m => m.UserID)
<div class="form-group">
@Html.LabelFor(m => m.UserName, new { @class = "col-md-2 control-label" })
<div class="col-md-10">
@Html.TextBoxFor(m => m.UserName, new { @class = "form-control", @readonly = "readonly" })
@Html.ValidationMessageFor(m => m.UserName, "", new { @class = "text-danger" })
</div>
</div>
<div class="form-group">
@Html.LabelFor(m => m.RoleName, new { @class = "col-md-2 control-label" })
<div class="col-md-10">
@Html.DropDownListFor(m => m.RoleName, new SelectList(Model.AssignedRoles, "Value", "Text"), Resources.DropdownSelect, new { @class = "form-control" })
</div>
</div>
<div class="form-group">
<div class="col-md-offset-2 col-md-10">
<input type="submit" value="@Resources.Remove" class="btn btn-default" />
</div>
</div>
}
Finally, here's the controller with the actions they make use of:
UserController.cs
//
// GET: /User/AssignRole
[Authorize(Roles = "Admin")]
[HttpGet]
public ActionResult AssignRole(string userID)
{
var user = context.Users.Where(u => u.Id == userID).FirstOrDefault();
var vm = new UserAssignRoleViewModel();
vm.UserID = user.Id;
vm.UserName = user.UserName;
List<IdentityRole> unassignedRoles = new List<IdentityRole>();
foreach (var role in context.Roles)
{
if (this.UserManager.IsInRole(vm.UserID, role.Name) == false)
{
unassignedRoles.Add(role);
}
}
vm.UnassignedRoles = unassignedRoles.OrderBy(r => r.Name).Select(rr => new SelectListItem { Value = rr.Name.ToString(), Text = rr.Name }).ToList();
return View(vm);
}
//
// POST: /User/AssignRole
[Authorize(Roles = "Admin")]
[HttpPost]
public ActionResult AssignRole(UserAssignRoleViewModel vm)
{
this.UserManager.AddToRole(vm.UserID, vm.RoleName);
ViewBag.ResultMessage = Resources.RoleAssignedSuccessfully;
List<IdentityRole> unassignedRoles = new List<IdentityRole>();
foreach (var role in context.Roles)
{
if (this.UserManager.IsInRole(vm.UserID, role.Name) == false)
{
unassignedRoles.Add(role);
}
}
vm.UnassignedRoles = unassignedRoles.OrderBy(r => r.Name).Select(rr => new SelectListItem { Value = rr.Name.ToString(), Text = rr.Name }).ToList();
return View(vm);
}
//
// GET: /User/RemoveRole
[Authorize(Roles = "Admin")]
[HttpGet]
public ActionResult RemoveRole(string userID)
{
var user = context.Users.Where(u => u.Id == userID).FirstOrDefault();
var vm = new UserRemoveRoleViewModel();
vm.UserID = user.Id;
vm.UserName = user.UserName;
vm.AssignedRoles = context.Roles.OrderBy(r => r.Name).ToList().Select(rr => new SelectListItem { Value = rr.Name.ToString(), Text = rr.Name }).ToList();
List<IdentityRole> assignedRoles = new List<IdentityRole>();
foreach (var role in context.Roles)
{
if (this.UserManager.IsInRole(vm.UserID, role.Name) == true)
{
assignedRoles.Add(role);
}
}
vm.AssignedRoles = assignedRoles.OrderBy(r => r.Name).Select(rr => new SelectListItem { Value = rr.Name.ToString(), Text = rr.Name }).ToList();
return View(vm);
}
//
// POST: /User/RemoveRole
[Authorize(Roles = "Admin")]
[HttpPost]
public ActionResult RemoveRole(UserRemoveRoleViewModel vm)
{
if (this.UserManager.IsInRole(vm.UserID, vm.RoleName))
{
this.UserManager.RemoveFromRole(vm.UserID, vm.RoleName);
ViewBag.ResultMessage = Resources.RoleUnassignedSuccessfully;
List<IdentityRole> assignedRoles = new List<IdentityRole>();
foreach (var role in context.Roles)
{
if (this.UserManager.IsInRole(vm.UserID, role.Name) == true)
{
assignedRoles.Add(role);
}
}
}
else
{
ViewBag.ResultMessage = Resources.ThisUserDoesNotBelongToSelectedRole;
}
return View (vm);
}
Here's the issue:
The dropdown has to get repopulated everytime, either assigning roles to users or removing them. Everything works fine in the assigning roles side; it only shows the unassigned roles in the dropdown, and when you add a role, coming back from the POST action it shows the refreshed dropdown without the role you just assigned.
But in the removing roles side, as soon as you remove a role from a user (which it DOES correctly), coming back to the view from the POST action it throws the exception
Value cannot be null. Parameter name: items
in the line
@Html.DropDownListFor(m => m.RoleName, new SelectList(Model.AssignedRoles, "Value", "Text"), Resources.DropdownSelect, new { @class = "form-control" })
My guess is that since in the POST Action method RemoveRole I'm not changing in any way the RoleName property of the UserRemoveRoleViewModel, and coming back to the view the dropdown has been repopulated, the m => m.RoleName crashes because it's looking for the already removed role, which is not in the list anymore. Hope I'm explaining myself well enough.
The problem is that I have absolutely no idea on how to fix this. Any help?
