I'm trying to do a very simple Html helper in Asp.net MVC 5:
#helper GetMyTextArea()
{
#Html.TextArea("myText")
}
Then i try to include it in my view: (the helper is in a file called MyHelp.cshtml, located in the App_Code Folder)
#MyHelp.GetMyTextArea()
If i render my view now, i get following exception:
System.NullReferenceException:
System.Web.WebPages.HelperPage.Html.get returned null.
Anyone know this issue? I think i can work around it with a partial view but this shouldn't be a problem with a html helper.
There are certain limitations apply when using #helper in App_Code folder, such like no direct access to standard HtmlHelper methods (you need to pass it manually by including it in your method, e.g. #helper GetMyTextArea(HtmlHelper Html)). You can add #functions which enables direct access to HtmlHelper methods:
#functions {
public static WebViewPage page = (PageContext.Page as WebViewPage);
public static HtmlHelper<object> html = page.Html;
}
Hence, MyHelp.cshtml content should be like this:
// adapted from /a/35269446/
#functions {
public static WebViewPage page = (PageContext.Page as WebViewPage);
public static HtmlHelper<object> html = page.Html;
}
#helper GetMyTextArea()
{
#Html.TextArea("myText")
}
Afterwards, you can call the helper method in view page as #MyHelp.GetMyTextArea() without passing HtmlHelper manually.
Similar issues:
Razor: Declarative HTML helpers
Using #Html inside shared #helper in App_Code
Related
Sory about my question, I am brand new to MVC 4 Razor, it's different from Asp.NET Web form.
Look like joomla, and other web languague, how can i create a "module", eg: "news, ads, counter" and stick it to asp.NET page.
I have a layout.cshtml in share folder, i think it's "Master Page" (like Master Page in Asp.NET webform)
How can i create some positions in that layout ?
You can create partial views or controller/actions that return a partial.
Partial Views
First create a partial view (which is a razor view without boilerplate markup like doctype, html and body elements.
To use a partial view in Razor:
#Html.Partial("name-of-partial-view", model-for-the-partial-view)
Actions returning a partial
To have a controller create a partial for you, create an action like this:
public DemoController : Controller
{
[ChildActionOnly] // Optional attribute, making this action invisible to the routing system
public ActionResult Demonstration(string someparam)
{
// Do something with someparam to get information to display
return PartialView();
}
}
You'll need to create a partial view to be returned from this action. (As before, a partial doesn't have the boilrplate markup like doctype, html and body.)
And to call it from Razor:
#Html.Action("Demonstration", "Demo", new { someparam = "something" });
If you want this partial on every page, put it somewhere in your layout page.
UPDATE1
I've added RazorGenerator and etc...
After set custom tools, I've seen generated code for my razor pages.
Added this code in assembly
public class MyAreaRegistration : AreaRegistration
{
public override void RegisterArea(AreaRegistrationContext context)
{
context.MapRoute("Dictionary_default", "MyDictionary/{Action}/", new { controller = "DictionaryControllerBase", action = "Index" });
}
public override string AreaName
{
get { return "MyDictionary"; }
}
#endregion
}
But when I open page by url /MyDictionary, i see "Unable to find the resource."
NOTE I use in my project MVC3 and Spring.Net
I use one controller (base controller) in another Assembly with razor pages.
In my project I make controller inherited from base controller, just it make some settings. But razor pages I wish to use from assembly.
How can I do it?
You could the RazorGenerator extension. I have detailed how this can be achieved in the following post. The idea is that the RazorGenerator extension would create a corresponding .cs file for each Razor view and it will update it every-time you make a change to the corresponding view. This way the Razor views will be precompiled in the class library along with their respective controllers and view models. The RazorGenerator.Mvc NuGet will then register a custom virtual path provider which will take care of resolving those views.
I used the following tutorial to help me build an RSS Reader in my ASP.NET MVC3 Razor application:
http://weblogs.asp.net/jalpeshpvadgama/archive/2011/08/17/creating-basic-rss-reader-in-asp-net-mvc-3.aspx
However, unlike the tutorial example, I want the RSS feed to be displayed on every page, and have therefore added it to my layout file, /Views/Shared/_Layout.cshtml
I currently only have 2 views on my site, and to get the RSS Reader to work on both views I've got the following code in my HomeController:
public class HomeController : Controller
{
//
// GET: /Index/
public ActionResult Index()
{
return View(CT.Models.RssReader.GetRssFeed());
}
public ActionResult About()
{
return View(CT.Models.RssReader.GetRssFeed());
}
}
From my WebForms experience, I would simply add the RSS Reader code in my master page code behind, and it would automatically work on every page.
Is there a Controller for layout pages which allows me to do the same?
How can I get this to work on every call of the layout page, without having to return anything?
EDIT: Following #Sebastian's advice, I've now added this code to a Partial View, removed CT.Models.RssReader.GetRssFeed() from return View() and included this in my layout file:
#Html.Partial("_MyPartialView")
The code in this partial view is:
<ul>
#foreach (var item in Model)
{
<li>
#item.Title
</li>
}
</ul>
However, I'm not getting a runtime error:
Object reference not set to an instance of an object.
It's erroring on the line #foreach (var item in Model)
You have to create a partial view and add functionality there.
Then in your layout, render this partial.
EDIT
Is your partial view really a partial view? The reason I said that is because you have "_" in front of the name which suggests that it might be a layout (might just be a naming convention).
To fix object reference error, you have to add the #Model declaration on top of your partial view.
Hope it helps.
UPDATE
In order to use different model in partial view, you need to explicitly declare which model you are going to use on render partialmethod.
#{Html.RenderPartial("../YourFeed", Model.YourFeedModel);}
Let me know if that resolved your issue.
The new error you are having is due to you not passing a Model to the partial view. You can do this with the second argument of the Html.Partial function...
Html.Partial("ViewName", MyModel);
As I think you are trying to do this in a Layout page you could also consider using a static reference to get your RSS feed. So forget about needing to pass in a Model and in your partial have:
#foreach (var item in RssRepository.GetFeed())
{
<li>
#item.Title
</li>
}
this like to a class something like...
public static RssRepository
{
public static MyModel GetFeed()
{
return new MyModel();//<- return what you would normally pass as a Model for RSS feeds
}
}
Hope that all makes sense
i want dynamically create ascx files, to partial render them.
but as i know, ot show them , i at least need dummy method:
public ActionResult test()
{
return PartialView();
}
how can i create this method for each new ascx file?
upd: i need factory?
Why would you create dynamic ascx files?
If you want to create all the layout in the controller you should be able to return it directly.
But then, why would you do that?
This way it will be really hard to do unit testing and refactoring and reuse.
You'd need to create your .ascx controls ahead of time. If you are doing this, I would recommend that you register a new view engine to provide a new PartialView location.
public class MyViewEngine : WebFormsViewEngine
{
public MyViewEngine()
{
PartialViewLocationFormats = new[]
{
"~/Views/{1}/{0}.ascx",
"~/Views/GeneratedControls/{0}.ascx",
"~/Views/Shared/{0}.ascx"
};
}
}
This allows you to write your dynamic views to the /Views/GeneratedControls/ folder. If you need to use a specifically named control (i.e. the control you generate has a random name) then you simply need to adjust your call to PartialView:
public ActionResult test()
{
return PartialView("name-of-control");
}
Otherwise MVC will use the name of the Action as the name of the control to use.
I am migrating a web site to a new one using ASP .NET MVC2.
In the original site, master page has code-behind to check a query string parameter value. Depending on this value, code-behind dynamically modify some CSS property to hide / display master page elements.
As MVC2 has no code-behind because we are supposed to perform everything in the controllers, how should I proceed in this case ?
I see this : asp.net mvc modifying master file from a view
It partially answers my needs but the query string processing is common to all pages. How can I move this processing in a common code section ?
Regards.
A helper method looks like a good place:
public static class HtmlHelperExtensions
{
public static string GetCss(this HtmlHelper htmlHelper)
{
// read some request parameter
// here you also have access to route data so the
// parameter could be part of your custom routes as well
var foo = htmlHelper.ViewContext.HttpContext.Request["foo"];
// based on the value of this parameter
// return the appropriate CSS class
return (foo == "bar") ? "barClass" : "fooClass";
}
}
And somewhere in your master page:
<body class="<%= Html.GetCss() %>">
Or if you are always going to apply it to the body tag only it might be more appropriate to do this in order to reduce the tag soup:
public static class HtmlHelperExtensions
{
public static MvcHtmlString StartBody(this HtmlHelper htmlHelper)
{
var body = new TagBuilder("body");
var foo = htmlHelper.ViewContext.HttpContext.Request["foo"];
var bodyClass = (foo == "bar") ? "barClass" : "fooClass";
body.AddCssClass(bodyClass);
return MvcHtmlString.Create(body.ToString(TagRenderMode.StartTag));
}
}
and in your master page at the place of the body tag:
<%= Html.StartBody() %>
I can think of two solutions to this:
Derive your controllers from one controller base and set the ViewData parameter there depending on posted Form values
Don't use ViewData at all, but simply look for the form value in the view (using HttpContext.Current)
The second method violates the MVC pattern. IMO it is still acceptable in some scenarios, for example I am using this approach to highlight the currently selected item in a navigation menu.