C# Centralizing repeating VIewData in MVC

Question

When a user log in into my application i want to show his name throughout the whole application. I am using the asp.net MVC framework. But what i don't want is that is have to put in every controller something like:

ViewData["User"] = Session["User"];

This because you may not repeat yourself. (I believe this is the DRY [Don't Repeat Yourself] principle of OO programming.) The ViewData["User"] is on my masterpage. So my question is, what is a neat way to handle my ViewData["User"] on one place?

Photostat

Answer 1

You can do this fairly easily in either a controller base-class, or an action-filter that is applied to the controllers/actions. In either case, you get the chance to touch the request before (or after) the action does - so you can add this functionality there.

For example:

public class UserInfoAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(
        ActionExecutingContext filterContext)
    {
        base.OnActionExecuting(filterContext);
        filterContext.Controller.ViewData["user"] = "Foo";
    }
}
...
[HandleError, UserInfo]
public class HomeController : Controller
{...}

(can also be used at the action (method) level)

---

or with a common base-class:

public abstract class ControllerBase : Controller
{
    protected override void OnActionExecuting(
        ActionExecutingContext filterContext)
    {
        ViewData["user"] = "Bar";
        base.OnActionExecuting(filterContext);
    }
}

[HandleError]
public class HomeController : ControllerBase
{...}

Lafollette

Thnx, i'll try the base-class. But why overriding the OnActionExecuting() method? What does this method do? What is it's purpose? – Photostat

It executes just before your action (method) is executed. If you want, you could probably use OnActionExecuted instead, which executes immediately after your action is executed. – Lafollette

OKay, and because i am putting this in my base class, it affects al my actions within the controller? – Photostat

Correct. That is also true of the action-filter approach where you put the [UserInfo] at the class level (rather than the method level). – Lafollette

Answer 2

It's been a year, but I've just stumbled across this question and I believe there's a better answer.

Jimmy Bogard describes the solution described in the accepted answer as an anti-pattern and offers a better solution involving RenderAction: http://www.lostechies.com/blogs/jimmy_bogard/archive/2009/06/18/the-filter-viewdata-anti-pattern.aspx

Postremogeniture

Answer 3

Create a base class for your models with UserName property:

public abstract class ModelBase
{
    public string UserName { get; set; }
}

Create a base class for you controllers and override it's OnActionExecuted method. Within it check if model is derrived from BaseModel and if so, set it's UserName property.

public class ControllerBase : Controller
{
    protected override void OnActionExecuted(
        ActionExecutedContext filterContext)
    {
        var modelBase = ViewData.Model as ModelBase;

        if (modelBase != null)
        {
            modelBase.UserName = "foo";
        }

        base.OnActionExecuted(filterContext);
    }
}

Then you will be able to display user's UserName in the view like this:

<%= Html.Encode(Model.UserName) %>

See also:

• ASP.NET MVC Best Practices, Tips and Tricks

Gangboard

"check if model is derrived from BaseModel and .." how do I do this? Can you give me an example? – Photostat

I think I get your solution. But I isn't it a little complicated? Doesn't do the common base-class of Marc Gravell the same thing in a way? – Photostat

@Martijn, it allows you working with strongly typed model instead of ViewData[..] dictionary. With it you have intellisence support in your views etc etc. – Gangboard

@KonstantinTarkus - shouldn't that be var modelBase = ViewData.Model as BaseModel; ? – Beanery

Answer 4

Another method for providing persistent model data through out your entire application is by overriding the DefaultFactoryController with your custom one. In your CustomerFactoryController, you would hydrate the ViewBag with the model you are wanting to persist.

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