Displaying Error in a View - error-handling

Question

Is there any standard practice to display errors in a view? Currently it is being displayed from TempData.
I implemented a derived a class from Base Controller and used that derived class in every one of my controller. Then assign error or success messages from controller.
public class TestController : Controller
{
public string ErrorMessage
{
get { return (string) TempData[CommonHelper.ErrorMessageKey]; }
set
{
if (TempData.ContainsKey(CommonHelper.ErrorMessageKey))
{
TempData[CommonHelper.ErrorMessageKey] = value;
}
else
{
TempData.Add(CommonHelper.ErrorMessageKey,value);
}
TempData.Remove(CommonHelper.SuccessMessageKey);
}
}
public string SuccessMessage
{
get { return (string)TempData[CommonHelper.SuccessMessageKey]; }
set
{
if(TempData.ContainsKey(CommonHelper.SuccessMessageKey))
{
TempData[CommonHelper.SuccessMessageKey] = value;
}
else
{
TempData.Add(CommonHelper.SuccessMessageKey, value);
}
TempData.Remove(CommonHelper.ErrorMessageKey);
}
}
}
CommonHelper Class
public class CommonHelper
{
public const string SuccessMessageKey = "successMessage";
public const string ErrorMessageKey = "errorMessage";
public static string GetSuccessMessage(object data)
{
return data == null ? string.Empty : (string) data;
}
public static string GetErrorMessage(object data)
{
return data == null ? string.Empty : (string) data;
}
}
Then created a partial view having this
#using Web.Helpers
#if (!string.IsNullOrEmpty(CommonHelper.GetSuccessMessage(TempData[CommonHelper.SuccessMessageKey])))
{
<div class="alert alert-success">
#CommonHelper.GetSuccessMessage(TempData[CommonHelper.SuccessMessageKey])
</div>
}
else if (!string.IsNullOrEmpty(CommonHelper.GetErrorMessage(TempData[CommonHelper.ErrorMessageKey])))
{
<div class="alert alert-success">
#CommonHelper.GetErrorMessage(TempData[CommonHelper.ErrorMessageKey])
</div>
}
And in every view, the partial view is rendered.
<div>
#Html.Partial("_Message")
</div>

Answer 1

Here is a pretty common implementation of displaying errors.
Controller
public class UserController : Controller
{
[HttpPost]
public ActionResult Create(User model)
{
// Example of manual validation
if(model.Username == "Admin")
{
ModelState.AddModelError("AdminError", "Sorry, username can't be admin")
}
if(!ModelState.IsValid()
{
return View(model)
}
}
}
Model
public class User
{
[Required]
public string Username {get; set;}
public string Name {get; set; }
}
View
#Html.ValidationSummary(true)
#using(Html.BeginForm())
{
// Form Html here
}
You don't need all of the infrastructure you created. This is handled by the framework. If you need a way to add success messages you can checkout the Nuget Package MVC FLASH

Answer 2

I prefer to use ModelState.AddModelError()