Dynamic layout in Web App with MVC 4

Question

I've had a MVC 4 / Entity web project dropped into my lap, and I've never used either before. I'm getting through it but the simple things are really tripping me up - Like hiding or displaying a link in my layout based on a parameter in the database.

I created a function in my HomeController that simply sets 2 bools in the ViewBag for whether or not a person is a manager or superuser. I call that function using

@Html.Action("SetupViewBag", "Home")

which sits right after the <body> tag in my layout. Here is the code for SetupViewBag:

public void SetupViewBag()
{
   ViewBag.IsManager = ADAccess.IsManager(SessionManager.GetUserName());
   ViewBag.IsSuper = SessionManager.SuperUser();
}

The bools are set properly and in the right order when I set up break points, but when I try to access them using the below code, I get a 'Cannot convert null to 'bool' because it is a non-nullable value type.'

@{
   if((bool)@ViewBag.IsManager){                       
      <li>@Html.ActionLink("Management", "Management", "Home",null, new { id = "managementLink" })</li>
   }                     
}

There has to be something really simple I'm missing. Any help is greatly appreciated.

When you say "bools are set properly" you mean you have ViewBag.IsManager=true (or false) in your code? And that you do not have it inside an if-else that would make it null on the view? — von v.
– von v., Commented Mar 26, 2013 at 6:31
Updated question with the SetupViewBag code. When I set a break point inside SetupViewBag and on the if((bool)@ViewBag.IsManager){ line, the ViewBag.IsManager is set before it is referenced. However, it is referenced in the layout file, not a view per-se, which I believe to be my problem after ongoing research. — Dakine83
– Dakine83, Commented Mar 26, 2013 at 6:36

von v. · Accepted Answer · 2013-03-26 06:50:47Z

2

Based on your comment, @Dakine83, you should setup your ViewBag on the controller constructor method like so:

public class YourController : BaseController {
    public YourController(){

    }
}

The reason for that is because the Layout page is already rendered the time your action method has been called. The reason you have a null ViewBag.IsManager.

UPDATE: Use a base controller

public class BaseController : Controller {
    public BaseController() {
            ViewBag.IsManager = ADAccess.IsManager(SessionManager.GetUserName());
    }
}

edited Mar 26, 2013 at 6:50

answered Mar 26, 2013 at 6:42

von v.

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2 Comments

Dakine83 Over a year ago

That's what I was afraid of. Is the only option to have the exact same function on each of my 8 controllers? That seems ridiculous, but not surprising.

von v. Over a year ago

No, you can have, and I suggest "should have", a base controller. See my updated answer.

khush · Accepted Answer · 2013-03-26 06:38:21Z

1

i hope this might work for you,please try it once @Html.ActionLink("Management", "Management", "Home", new { id = false }, null);

Thanks

answered Mar 26, 2013 at 6:38

khush

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3 Comments

Dakine83 Over a year ago

The link works just fine - it's the check to see if the link should be displayed that is breaking.

khush Over a year ago

I get a 'Cannot convert null to 'bool' because it is a non-nullable value type i think you have mention above issue, and it will be resolved if you set new { id = true/false } as the parameter in the actin methos is of bool type.

Dakine83 Over a year ago

The 'cannot convert' is not coming from that line. That line works as expected without the if around it.

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