[c#] MVC Razor Hidden input and passing values

I am pretty sure I am doing something wrong here. Over the last 2 months we have been developing a web app using MVC and Razor and we never thought of using the form element. Now so much has already been done with master pages and sub pages that it means restructuring most of our code in order to use form element and the would result in multiple form elements on a page.

That aside, in Asp.Net if I wanted to access any control in the C# code behind I could just give it an ID="SomeID" and a RUNAT="SERVER". Then in my code behind I could set its value and properties.

When I do this in Razor, we use lines like:

 <input id="hiddenPostBack" runat="server" type="hidden" />

Why can't I access this in the controller? I want to detect a postback and set the value to false if it is the first time the page loads, and if not, then set the value to true. Then based on this, I will read it either server side or client side and do something.

My real question is, how do I "do something" both server side and client side given that I don't have a form element. I was under the impression that if I wanted to pass values from client to server and back, the easiest way to do this is with a hidden input. But I am just not getting how to accomplish this with MVC3 and razor.

Thanks in advance for your help.

First of all ASP.NET MVC does not work the same way WebForms does. You don't have the whole runat="server" thing. MVC does not offer the abstraction layer that WebForms offered. Probabaly you should try to understand what controllers and actions are and then you should look at model binding. Any beginner level tutorial about MVC shows how you can pass data between the client and the server.

As you may have already figured, Asp.Net MVC is a different paradigm than Asp.Net (webforms). Accessing form elements between the server and client take a different approach in Asp.Net MVC.

You can google more reading material on this on the web. For now, I would suggest using Ajax to get or post data to the server. You can still employ input type="hidden", but initialize it with a value from the ViewData or for Razor, ViewBag.

For example, your controller may look like this:

public ActionResult Index()
{
     ViewBag.MyInitialValue = true;
     return View();
} 

In your view, you can have an input elemet that is initialized by the value in your ViewBag:

<input type="hidden" name="myHiddenInput" id="myHiddenInput" value="@ViewBag.MyInitialValue" />

Then you can pass data between the client and server via ajax. For example, using jQuery:

$.get('GetMyNewValue?oldValue=' + $('#myHiddenInput').val(), function (e) {
   // blah
});

You can alternatively use $.ajax, $.getJSON, $.post depending on your requirement.

You are doing it wrong since you try to map WebForms in the MVC application.

There are no server side controlls in MVC. Only the View and the Controller on the back-end. You send the data from server to the client by means of initialization of the View with your model.

This is happening on the HTTP GET request to your resource.

[HttpGet]
public ActionResult Home() 
{
  var model = new HomeModel { Greeatings = "Hi" };
  return View(model);
}

You send data from client to server by means of posting data to server. To make that happen, you create a form inside your view and [HttpPost] handler in your controller.

// View

@using (Html.BeginForm()) {
  @Html.TextBoxFor(m => m.Name)
  @Html.TextBoxFor(m => m.Password)
}

// Controller

[HttpPost]
public ActionResult Home(LoginModel model) 
{
  // do auth.. and stuff
  return Redirect();
}

If you are using Razor, you cannot access the field directly, but you can manage its value.

The idea is that the first Microsoft approach drive the developers away from Web Development and make it easy for Desktop programmers (for example) to make web applications.

Meanwhile, the web developers, did not understand this tricky strange way of ASP.NET.

Actually this hidden input is rendered on client-side, and the ASP has no access to it (it never had). However, in time you will see its a piratical way and you may rely on it, when you get use with it. The web development differs from the Desktop or Mobile.

The model is your logical unit, and the hidden field (and the whole view page) is just a representative view of the data. So you can dedicate your work on the application or domain logic and the view simply just serves it to the consumer - which means you need no detailed access and "brainstorming" functionality in the view.

The controller actually does work you need for manage the hidden or general setup. The model serves specific logical unit properties and functionality and the view just renders it to the end user, simply said. Read more about MVC.

Model

public class MyClassModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string MyPropertyForHidden { get; set; }
}

This is the controller aciton

public ActionResult MyPageView()
{
    MyClassModel model = new MyClassModel(); // Single entity, strongly-typed
    // IList model = new List<MyClassModel>(); // or List, strongly-typed
    // ViewBag.MyHiddenInputValue = "Something to pass"; // ...or using ViewBag

    return View(model);
}

The view is below

//This will make a Model property of the View to be of MyClassModel
@model MyNamespace.Models.MyClassModel // strongly-typed view
// @model IList<MyNamespace.Models.MyClassModel> // list, strongly-typed view

// ... Some Other Code ...

@using(Html.BeginForm()) // Creates <form>
{
    // Renders hidden field for your model property (strongly-typed)
    // The field rendered to server your model property (Address, Phone, etc.)
    Html.HiddenFor(model => Model.MyPropertyForHidden); 

    // For list you may use foreach on Model
    // foreach(var item in Model) or foreach(MyClassModel item in Model)
}

// ... Some Other Code ...

The view with ViewBag:

// ... Some Other Code ...

@using(Html.BeginForm()) // Creates <form>
{
    Html.Hidden(
        "HiddenName",
        ViewBag.MyHiddenInputValue,
        new { @class = "hiddencss", maxlength = 255 /*, etc... */ }
    );
}

// ... Some Other Code ...

We are using Html Helper to render the Hidden field or we could write it by hand - <input name=".." id=".." value="ViewBag.MyHiddenInputValue"> also.

The ViewBag is some sort of data carrier to the view. It does not restrict you with model - you can place whatever you like.