How can I retrieve a property value from modelstate in httppost action.
Below is the code, I used to retrive the hidden id field from modelstate. But is it not possible to have strongly typed version to get value. Like, if property name is modified, prompting a compile time error.
Could anyone please explain difference between "AttemptedValue" and "RawValue".
ModelState state;
if (ModelState.TryGetValue("id", out state))
{
string value = state.Value.AttemptedValue.ToString();
}
Attempted value is used by the framework and it contains concatenated list of values. In my case, since it is id field, I am going ahead with attempted value. Below link has more information on this.
http://forums.asp.net/t/1571473.aspx/1?MVC+2+Custom+ModelBinder+and+storing+the+attempted+value+for+the+view
you can iterate the ModelStateDictionary object and through the keys(property name) on the dictionary get the value of the desired property or you can do something like ModelState["PropertyName"].Value
Related
A simple scenario that I've never seen before, but a colleague has just hit - MVC3
Create an action method MyAction(int myProperty = 0)
Create a model that has a property MyProperty
Pass an instance of this model to a strongly typed view, but set the property to 10 in code (don't use the query string parameter!)
In the view, Html.TextBoxFor(x => x.MyProperty)
This should render 10 in the text box.
Now call the action method MyAction?myProperty=8
Shouldn't this still render 10 in the text box?
I see that I can override the property discovered by the expression and assume this is because they are the same name (Query String parameter and model property). Eveything is then in the ViewData but one overrides the other.
Is this by design?
This is by design - ModelState is the highest priority value-provider for model properties, higher than even model itself. Without query string parameter, ModelState does not contain value for MyProperty, so framework uses model value.
You can use ModelState.Remove("MyProperty") to ensure using model value
If you look at the source code for Html.TextBoxFor you will see that if a value exists in ModelState then it will always use that value before any other.
string attemptedValue = (string)htmlHelper.GetModelStateValue(fullName, typeof(string));
tagBuilder.MergeAttribute("value", attemptedValue ?? ((useViewData) ? htmlHelper.EvalString(fullName, format) : valueParameter), isExplicitValue);
If the value is in ModelState, then it doesn't matter what you set in code.
I'm having trouble with this line of code: #{Html.RenderPartial("Form", Model.Contact);}
This is the error I'm getting:
The model item passed into the dictionary is of type 'ContactWeb.Models.RoleListViewModel', but this dictionary requires a model item of type 'ContactWebLibrary.Contact'.
I have RoleListViewModel listed at the top of the view and I have Contact property in my RoleListViewModel so I'm not sure why it's complaining. Can anyone please help me to fix this problem? Thanks.
As a third parameter, you need to pass in a new ViewDataDictionary.
In response to your comment:
"In the Form, on the line , it is giving a NullReferenceException that the object reference is not set to the instance of an object."
MVC3 requires that you use the Html Helper to pass input as it adds some additional markup.
#Html.Hidden("currentId", #Model.Id)
And then in your [HttpPost] controller
public ActionResult someController(int currentId)
{
//Use current Id
return RedirectToAction("responseController");
}
I have a textbox that I am trimming the value of server side in the viewModel's setter and verifying that the trimmed value is present:
<Required()>
Public Property Name As String
Get
Return Me.mName
End Get
Set(value As String)
Me.mName = value.Trim()
End Set
End Property
In the controller, I check to see if the ModelState is invalid, and if it is, I show the view again:
If (Not ModelState.IsValid) Then
Return View("Locations", viewModel)
End If
In situations where the trimmed value is blank, I re-display the form to the user. At this point, the non-trimmed values are put into the textbox. I would much prefer the trimmed value.
I was looking through the MVC sourcecode, and I found that at one point in the InputHelper function (used by Html.Textbox(), located in InputExtensions.cs) the code was checking the ModelState for the value, and if it existed, replacing the controller-supplied value.
string attemptedValue = (string)htmlHelper.GetModelStateValue(name, typeof(string));
tagBuilder.MergeAttribute("value", attemptedValue ?? ((useViewData) ? htmlHelper.EvalString(name) : valueParameter), isExplicitValue);
I realize that I could fix this by clearing the ModelState in the controller, but I'm just wondering why the MVC Developers chose to have the values in the ModelState supersede the view model values.
This was designed this way because the assumption is if you are not redirecting to another view after a post .. Hence the post-redirect-get pattern, then there was ideally an error and the current posted values would be shown back to the user for them to fix hence why they are pulled from modelstate. You can ModelState.Clear to work with this but keep that design in mind.
After a user clicks the submit button of my page, there is a textbox that is validated, and if it's invalid, I show an error message using the ModelState.AddModelError method. And I need to replace the value of this textbox and show the page with the error messages back to the user.
The problem is that I can't change the value of the textbox, I'm trying to do ViewData["textbox"] = "new value"; but it is ignored...
How can I do this?
thanks
You can use ModelState.Remove(nameOfProperty) like:
ModelState.Remove("CustomerId");
model.CustomerId = 123;
return View(model);
This will work.
I didn't know the answer as well, checked around the ModelState object and found:
ModelState.SetModelValue()
My model has a Name property which I check, if it is invalid this happens:
ModelState.AddModelError("Name", "Name is required.");
ModelState.SetModelValue("Name", new ValueProviderResult("Some string",string.Empty,new CultureInfo("en-US")));
This worked for me.
I have a situation where I want to persist a hidden value between POST's to the controller. The hidden value is modified as other values are changed. I couldn't get the hidden element to update without updating the value manually in ModelState.
I didn't like this approach as it felt odd to not be using a strongly typed reference to Model value.
I found that calling ModelState.Clear directly before returning the View result worked for me. It seemed to then pick the value up from the Model rather than the values that were submitted in the previous POST.
I think there will likely be a problem with this approach for situations when using Errors within the ModelState, but my scenario does not use Model Errors.
Short: how does modelbinding pass objects from view to controller?
Long:
First, based on the parameters given by the user through a search form, some objects are retrieved from the database.
These objects are given meta data that are visible(but not defining) to the customer (e.g: naming and pricing of the objects differ from region to region).
Later on in the site, the user can click links that should show details of these objects.
Because these meta data are important for displaying, but not defining, I need to get the previously altered object back in the controller.
When I use the default asp.net mvc modelbinding, the .ToString() method is used. This off course doesn't return a relevant string for recreating the complete object.
I would have figured the ISerializable interface would be involved, but this is not so.
How should I go about to get the desired effect? I can't imagine I'm the first one to be faced with this question, so I guess I'm missing something somewhere...
The default model binding takes form parameters by name and matches them up with the properties of the type specified in the argument list. For example, your model has properties "Price" and "Name", then the form would need to contain inputs with ids/names "Price" and "Name" (I suspect it does a case insensitive match). The binder uses reflection to convert the form values associated with these keys into the appropriate type and assigns it to the properties of a newly created object of the type specified by the parameter (again derived by reflection).
You can actually look at (and download) the source for this at http://www.codeplex.com/aspnet, although you'll have to drill down into the MVC source from there. I'd give a link to the DefaultModelBinder source, but the way they are constructed, I believe the link changes as revisions are introduced.
So, to answer your question, you need to have parameters (could be hidden) on your form that correspond to the properties of the object that you want to recreate. When you POST the form (in the view) to the controller, the binder should reconstitute an object of the specified type using the form parameters. If you need to do translation from the values in the form parameter to the object properties, you'll probably need to implement your own custom model binder.
[EDIT] In response to your second post:
Let's say that we want to have a link back to an action that uses a customized object. We can store the customized object in TempData (or the Session if we need it to last more through more than one postback) with a particular key. We can then construct the action link and provide the key of the object as value to the ActionLink in an anonymous class. This will pass back the key as a Request parameter. In our action we can use the key from this parameter to retrieve the object from TempData.
<%= Html.ActionLink( ViewData["CustomObject1",
"Select",
new { TempDataKey = ViewData["CustomObject1_Key"] }
) %>
public ActionResult Select()
{
Entity custObj = null;
string objKey = Request.Params["TempDataKey"];
if (!string.IsNullOrEmpty(objKey))
{
custObj = (Entity)TempData[objKey];
}
... continue processing
}
#tvanfosson
Thanks for your explanation, but what about links? (no forms involved)
Currently the Html.ActionLink(c=>c.Action(parameter), "label") takes objects as parameter. These have to be translated into URL parts. For this, MVC ALWAYS goes to the .ToString() method. I don't want to serialize my object in the ToString method.
Shouldn't I be able to somehow help the framework serialize my object? Say through the ISerialize interface or something?