mvc

Creating custom Html Helper in MVC3

Posted on by trailmax

Creating custom attribute is pretty simple really, just follow the example. You need to return MvcHtmlString – that is string with your html to be displayed on a page – this will not be escaped.

public static MvcHtmlString DisplayWithNameFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper,Expression<Func<TModel, TProperty>> expression)
{
    ModelMetadata metaData = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
    if (metaData.Model == null)
    {
        return MvcHtmlString.Create(String.Empty);
    }

    string html = "<div class=\"display-label\">";
    html += htmlHelper.LabelFor(expression).ToString();
    html += "</div><div class=\"display-field\">";
    html += htmlHelper.DisplayFor(expression).ToString();
    html += "</div>";

    return MvcHtmlString.Create(html);
}

MVC Recipies: On Page Action Return to the previous page

Posted on by trailmax

Whenever you need a page to return to the previous page when you get an form submit or some other action, this can be used:

Have a base controller that is inherited by all your controllers. That is always a good idea – you can easily add things that work site-wide.
In you base controller have a OnActionExecuting overriden – here we are going to store the previous page.
Something like this:

public abstract partial class MyController : Controller
{

public ActionResult RedirectToPrevious(String defaultAction, String defaultController)
{
  if (Session == null || Session["PrevUrl"] == null)
  {
      return RedirectToAction(defaultAction, defaultController);
  }

  String url = ((Uri)Session["PrevUrl"]).PathAndQuery;

  if (Request.Url != null && Request.Url.PathAndQuery != url)
  {
      return Redirect(url);
  }

  return RedirectToAction(defaultAction, defaultController);
}


protected override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var httpContext = filterContext.HttpContext;

    if (httpContext.Request.RequestType == "GET"
        && !httpContext.Request.IsAjaxRequest()
        && filterContext.IsChildAction == false)    // do no overwrite if we do child action.
    {
        // stop overwriting previous page if we just reload the current page.
        if (Session["CurUrl"] != null 
            && ((Uri)Session["CurUrl"]).Equals(httpContext.Request.Url) ) 
            return;

        Session["PrevUrl"] = Session["CurUrl"] ?? httpContext.Request.Url;
        Session["CurUrl"] = httpContext.Request.Url;
    }
}
}

Now, as I figured, it is not the best idea for redirecting everything by default. For validation purposes you would like not to redirect

Then you can reference Session[“PrevUrl”] in controllers, but there is a better way of doing it – create attribute!

public class RedirectToPreviousPageAttribute : ActionFilterAttribute
{
///

/// Place [RedirectToPreviousPage] attribute on Controller action
/// and when you do submit of form, this functionality will kick in.
/// We check if Session has Previous URL set and force to redirect
/// to whatever it says.
/// If no Session variable is set, just do what it is supposed to do in the first place.
///

/// public override void OnResultExecuted(ResultExecutedContext filterContext)
{
var httpContext = filterContext.HttpContext;

    if (httpContext.Session == null || httpContext.Session["PrevUrl"] == null)
    {
        base.OnResultExecuted(filterContext);
        return;
    }

    String url = ((Uri)httpContext.Session["PrevUrl"]).PathAndQuery;

    if (httpContext.Request.Url != null && httpContext.Request.Url.PathAndQuery != url)
    {
        httpContext.Response.Redirect(url);
    }


    base.OnResultExecuted(filterContext);

}

}

And now, wherever you are put this attribute on a controller action (or entire controller), it will redirect to the previous page:

[HttpPost]
public virtual ActionResult Edit(Model model)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }

    _repository.InsertOrUpdate(model);
    _repository.Save();

    return RedirectToPrevious("Index", "Controller");
}

Voilà! Good to go!

Dependency resolver in .Net

Posted on by trailmax

Ninject is very cool and lightweight DI container.
But you can not always inject objects through constructor – sometimes you must have parameter-less constructor, like in MvcApplication object.
In that case you can use DependencyResolver from System.Web.Mvc namespace from System.Web assembly

_userDataService = 
DependencyResolver.Current.GetService<IUserDataService>();

Unfortunately MSDN documentation does not have much, only link to this blog post: http://bradwilson.typepad.com/blog/2010/10/service-location-pt5-idependencyresolver.html

Razor view: conditionally include debug versions of JS libraries

Posted on by trailmax

In Razor compiler directives do not work, cause Razor Views are not compiled.
So this would not work:

@{ #if DEBUG}

@{#else}

@{#endif}

But you can trick that thing into submission, thanks to this StackOverflow topic

A better, more generic solution is to use an extension method, so all views have access to it:

public static bool IsReleaseBuild()
{
#if DEBUG
    return false;
#else
    return true;
#endif
}

You can then use it like follows in any view (razor syntax):

@if(IsReleaseBuild())

Generate T4MVC templates

Posted on by trailmax

Everybody is talking how good the T4 templates, but nobody tells you how to generates the bloody things.

In VS2012 if you open command window (View-> Other Windows -> Command Window) and execute
TextTransformation.TransformAllTemplates – that should do the trick.

If you would like a button for that – add Build Toolbar Panel and it should contain “Transform All Templates” button.

Or you can install Chirpy and configure it to do T4MVC for you on every build: