CODEWITHSUNDEEP
asp.net-mvcglobal-variables
Jason
Jason

Reputation: 600

How to set a truly global variable in ASP.NET MVC 4?

I am building a site that will eventually pull images from a separate domain. That domain doesn't exist yet, nor has its name even been concluded upon, so for the time being I need to access images from a local directory. To avoid manually changing every single image tag later on, I want to use a global variable that I can change once and affect every single image tag on the website.

I have found one solution thus far, which is to set a key/value pair in Web.config's appSettings like so...

<appSettings>
  <add key="ImageSource" value="/some/local/directory" />
</appSettings>

Then, in each view, at the top, I add...

@{
  string imgsrc = System.Configuration.ConfigurationManager.AppSettings["ImageSource"];
}

And in the HTML I use...

<img src="@imgsrc/my_image.jpg" alt="my image" />

This works but it still requires me to assign the variable in every single view template that I create. In the spirit of DRY, I am looking for some way that I can assign the variable once and have its presence implicit in every page, regardless of model, controller, or view.

Upvotes: 1

Views: 4440

Answers (2)

M Smearer
M Smearer

Reputation: 361

I like using extension methods on the built-in HtmlHelper class for this type of thing. You can have an HtmlHelper extension such as:

    public static MvcHtmlString ImageReference(
        this HtmlHelper html,
        String id,
        String altText,
        String imageNameAndExtension)
    {

        var baseUrl = [go get the setting value];
        String src = String.Concat(baseUrl, imageNameAndExtension);

        var img = new TagBuilder("img");
        if (String.IsNullOrEmpty(id) == false) img.MergeAttribute("id", id);
        if (String.IsNullOrEmpty(altText) == false) img.MergeAttribute("alt", altText);
        img.MergeAttribute("src", src);

        return MvcHtmlString.Create(img.ToString(TagRenderMode.SelfClosing));

    }

Then consume like:

@Html.ImageReference("TheImage", "A Cool Image", "doublerainbow.png")

Usually you end up with a few overrides flowing through a single method (e.g. no id parameter, etc.) There are some really nice side-effects, too. If the whole team uses these, you end up with very standardized markup.

More Info: http://www.asp.net/mvc/tutorials/older-versions/views/creating-custom-html-helpers-cs

Upvotes: 1

Andy T
Andy T

Reputation: 9901

The easiest way would be to inject your logic into the request pipeline which gets executed each time so you just have to set it in one place. You would then need to set ImageSource in a place where it would be available to the views.

In the following example, I create a base controller that other controllers inherit from. Then override the OnActionExecuting method and set the ViewBag.

Now this value is available to all views where the controller inherits from BaseController.

public abstract class BaseController : Controller
{
  protected override void OnActionExecuting(ActionExecutingContext filterContext)
  {
      ViewBag.ImageSource = System.Configuration.ConfigurationManager.AppSettings["ImageSource"];
  }
}

Upvotes: 0

Related Questions