Textboxfor Displaying Initial Value, Not the Value Updated from Code

TextBoxFor displaying initial value, not the value updated from code

Your problem is (step by step)

1. Your SomeInformation() method sets the value of test1.Latitude
   to "LATITUDE2".
2. You then pass that model to your Index() method using the overload
   of RedirectToAction that accepts an object. Internally this uses
   reflection to build a RouteValueDictionary based on the properties
   of your model (in this case its simply latitude="LATITUDE2").
3. When you hit the Index method the model is bound by the DefaultModelBinder and now the value of DataSiteList.Latitude is "LATITUDE2" (which is why you enter
   the if block)
4. In the process of binding, the DefaultModelBinder sets the
   ModelStatevalue of Latitude to "LATITUDE2". Any attempts to set
   the value of Latitude are now ignored because the view uses
   ModelState value to render the control.

It not clear what your trying to do here. You can make it work as you expect by adding ModelState.Clear(); as the first line of your Index() method. This clears all existing ModelState values an you can now set the value to "LATITUDE".

But your if block makes no sense. Perhaps you were just doing some kind of test, but you may as well remove the parameter from the Index() method and just initialize a new instance of DataSites in the method.

Edit

To give a bit more information as to why updating a model property has no affect once ModelState has been set.

Imagine you have a form to collect user information where the model contains int Age. The user is asked to enter their age and someone enters "I'm five next week!". Of course this wont bind to an int so the DefaultModelBinder adds the value (the attemptedValue) and adds a ModelStateError.

When the view is returned it will typically display an error message such as "The field Age must be a number". If the html helper rendering the control used the model value, then it would display "0" (the default value for int). It would be somewhat confusing for the user to see "0" in the textbox and next it a message saying it must be a number (What! but zero is a number and what the heck happened to what I entered?). So instead, the helper uses the value from ModelState and now the users sees "I'm five next week!" and an associated error message that makes sense for the value.

So even though you thoughts were that "its not logical", there is actually some logic to this behavior.

MVC2 TextBoxFor value not updating after submit?

Default Html helper try to redisplay the data that is posted to them.
They first use the value from posted data and if no posted data is available they take the data from the Model.

This is not what you want obviously, but still the most common usage: You display some data in formfields after receiving a get request. You post to an Update action. If you have errors you want to redisplay the form with the values you entered still available.

I have seen some people getting around this (I think by writing to ModelState), but my choice was always to not use the default helpers if they dont help me. Thats especially true for hidden fields: Most people get confused when they set a value to a hidden field but the value that is realy used is from the post. At least there is a question every other day about it on SO :-)

Forget the "Most people" and replace it with "Everybody".

ASP.NET MVC: Hidden field value does not get rendered using HtmlHelper.Hidden

http://blog.johnwest.com/post/ASPNET-MVC-Hidden-Form-Field-Bug.aspx

http://blogs.msdn.com/b/simonince/archive/2010/05/05/asp-net-mvc-s-html-helpers-render-the-wrong-value.aspx?utm_medium=Twitter&utm_source=Shared

UPDATE
Oh I found another one from today (You are not alone):

How to update textbox value

How to set a default value with Html.TextBoxFor?

It turns out that if you don't specify the Model to the View method within your controller, it doesn't create a object for you with the default values.

[AcceptVerbs(HttpVerbs.Get)]
public ViewResult Create()
{
  // Loads default values
  Instructor i = new Instructor();
  return View("Create", i);
}

[AcceptVerbs(HttpVerbs.Get)]
public ViewResult Create()
{
  // Does not load default values from instructor
  return View("Create");
}

TextBoxFor value not updating after post

Use ModelState.Clear() before setting value

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Index(Repair r)
{
    ModelState.Clear(); //Added here
    r.Number = "New Value";
    return View(r);
}

HTML.TextBoxFor is set readonly before value set

When you post back a model, its values are added to ModelState. Html helpers bind to the vales in ModelState, not the values of the model properties, so modifying the value of a model property in the POST method will not be reflected in the view unless you first clear model state before setting the value using

ModelState.Clear(); // clears all properties

or

if (ModelState.ContainsKey("active"))
{
    ModelState["active"].Errors.Clear(); //clears the property 'active'
}

The reason for this behavior is explained in the second part of this answer.

However, clearing ModelState should be used with caution as it also clears validation errors, and in any case the correct approach is to follow the PRG pattern

Default value for TextBoxFor in ASP.NET MVC

Use TextBox instead of TextBoxFor

@Html.TextBox("WEIGHT", Model.WEIGHT ?? "0", new {...})

or if WEIGHT is an empty string

@Html.TextBox("WEIGHT", Model.WEIGHT == "" ? "0" : Model.WEIGHT, new {...})

View displays different values, then it has in its model

The issue is that when you submit your collection, the posted values are added to ModelState. If we look at just the Name property, the following values are added

Columns[0].Name // value = "a"
Columns[1].Name // value = "b"
Columns[2].Name // value = "c"

Now you insert a new column (say before the first item). The values in the model are now

Columns[0].Name // value = "ADDED"
Columns[1].Name // value = "a"
Columns[2].Name // value = "b"
Columns[3].Name // value = "c"

Now when you return the view, you (correcty) use the HtmlHelper methods to generate the view, but all the HtmlHelper methods that generate form controls render the value attribute by checking the following (in order)

1. the value in ModelState (if any)
2. the value in the ViewDataDictionary (if any)
3. the value from the model

The reason for this behavior is explained in TextBoxFor displaying initial value, not the value updated from code.

In the first iteration of the for loop, your @Html.TextBoxFor(m => m.Columns[i].Name) sees a value of "a" in ModelState and renders "a" in the textbox (even though the value of the model is "ADDED").

In the 2nd iteration, the value is again taken from ModelState, so "b" is rendered.

In the 3rd iteration, the value is again taken from ModelState, so "c" is rendered.

And in the 4th and final iteration, a value is not found in ModelState (or ViewData) for Columns[3].Name, so it reads the value from the model, so "c" is rendered.

As a side note, if you added @Model.Columns[i].Name in a table cell, you would see the values rendered in accordance with the property value i.e. Row 1: "ADDED", Row 2: "a", Row 3: "b", Row4: "c".

To solve this, you can add ModelState.Clear() before your return the view. However, the side effect of this is that it also clears any validation errors, so at the least, you should immediately return the view if ModelState is not valid

public ViewResult Index(CreateTableModels model, ...)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }
    ... // code to insert new row
    ModelState.Clear();
    return View(model);
}

However, the best approach is to follow the PRG pattern and redirect to a method that generates the new data.

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