I have an get action, which has a couple of parameters. In view I have a form, that fills after get action. Action creates an instance of model using received parameters, but if parameter has special value then action set to model some default values despite parameters. After that action return view with model.
The problem is that after changing the model in View shows data of the parameters, and not from the modified model.
This happens because, by design, all HTML helpers first look at the ModelState when binding and after that in the model itself. So if you intend to modify some value that was part of the POST request you will need to remove it from ModelState first if you want this change to be reflected in the view:
[HttpPost]
public ActionResult SomeAction(MyViewModel model)
{
// We remove the Bar property that was part of the request because
// we modify its value here
ModelState.Remove("Bar");
model.Bar = "Some modified value";
return View(model);
}
This assumes that in the corresponding view you have an input field for it:
#Html.EditorFor(x => x.Bar)
Related
I think i know some of the basics of MVC but there's one thing which I don't understand yet.
In the view Create which is generated automatically when you set up your project, how is data sent to the controller? I'm used to seeing ActionLinks with parameters but here there's no actionLink so I can't understand how data travel from the view to the controller.
Could you explain it to me please?
as you know, in your view, the very first line (usually) tells the view, about the Model being used within this view. like:
#model Models.CarViewModel
lets suppose, you have a form on this view, and it is posted to some action called Edit. Then you must have your Edit action, expecting the parameter of type you used as model in your view. like:
[HttpPost]
public ActionResult(CarViewModel model)
{
//logic
}
This convention is known as Strongly Typed View. Suppose Then you have some textbox for a property Name of your model as:
#Html.TextBoxFor(x => x.Name)
when the form is posted to Edit Action, the variable model in parameter of Edit action will be holding the respective values. i.e, model.Name
What is the most effective method in order to make all the fields on an MVC4 Razor empty when loading it (for example first loading or after backing to the page again)? If it is possible could you please suggest me a way with the help of Razor properties instead of using Javascript/jQuery.
It's a little difficult to make out what you're trying to do, but let's see if I can help.
Firstly, if you simply wanted to clear out a form's values after it's been posted, you can do that like so:
[HttpPost]
public ActionResult Index(ViewModel model)
{
ModelState.Clear();
model = new ViewModel();
return View(model);
}
Simply creating a new ViewModel isn't enough, as the ModelState dictionary will try to repopulate the form with the old values. This does what you want, but isn't really leveraging MVC to do what you want.
The better way to do it would be to redirect back to the action you use to display your form. Something like this:
public ActionResult Create()
{
var model = new ViewModel();
return View(model);
}
This is simply passing in an empty model to your form. Once the user fills out the form, and it's posted back to the server, you can handle it like so:
[HttpPost]
public ActionResult Create(ViewModel model)
{
if (ModelState.IsValid)
{
// Form data is valid so redirect back to display the form again
return RedirectToAction("Create");
}
// If we get here, redisplay the form with the fields filled in
// and errors shown
return View(model);
}
Simply calling a ModelState.Clear() will do the trick. You shouldn't have to instantiate the view model again.
A view displays (or collect) information about a Model.
So, if you pass an Empty model (that is: properties in null or blank or default values) it will "clear all fields".
All you have to do is invoking again the Action that displays the view, now passing an empty model.
EDIT:
You can do it in javascript, but then you have to duplicate and maintain the logic of what are default values.
I have the following model:
public class PersonListModel
{
....
[Required(ErrorMessage=AppConstants.MustSelectRecordToAttachMessage)]
public String SelectedPersonId { get; set; }
}
and the following view:
#using (Html.BeginForm("Attach", "Person", FormMethod.Post, new { #id = attachRecordFormId, targetDivId = personListId, #class = "inlineForm" }))
{
.....
#Html.HiddenFor(x => x.SelectedPersonId);
.....
<br />#Html.ValidationMessageFor(x => x.SelectedPersonId)
}
The hidden SelectedPersonId field is populated via some javascript hooked to the keyup event of one of the elements on my page.
My problem is that the required validation message shows immediately this partial view is displayed, not just when the form is submitted. It also displays again after the partial view is rendered again via an Ajax post.
I have very similar views that do not exhibit this problem, but 2 views (including the one above) that do exhibit this problem. I have been through a process of elimination to try to work out what is different between the views that work correctly and the 2 that exhibit this incorrect behavior, however I have not been able to locate the cause of the problem.
I presume that something is causing the unobtrusive validation to fire when the problem views are loaded. How can I track this down?
My problem is that the required validation message shows immediately this partial view is displayed
This could happen if the controller action that is displaying the view (containing the partial) takes the view model as argument:
public ActionResult Display(MyViewModel model)
{
... if this action is called with a GET request and you have missed
to pass a value for the "SelectedPersonId" query string parameter
you will get a validation error in the corresponding view
return View(model);
}
The reason for this happening is because your action is taking a model => the default model binder is kicking in attempting to populate your view model and when it attempts to set a value for the SelectedPersonId property it will automatically add a validation error to the model state if there's no corresponding value in the request because your model property is decorated with the [Required] attribute.
It also displays again after the partial view is rendered again via an Ajax post.
That's normal and could happen if the target POST action is taking your view model as argument and rendering a partial:
[HttpPost]
public ActionResult Process(MyViewModel model)
{
... if this action is called with a POST request and you have missed
to pass a value for the "SelectedPersonId" form parameter
you will get a validation error in the corresponding partial view
return PartialView(model);
}
So I have a ViewBag.Something and this data is randomly generated. In my view, I set this to a label like so #Html.LabelFor(m => m.Something, (string)ViewBag.Something). This works out well but when I submit the form there could be errors and if there are errors, I need this label to remain the same, I don't want dynamic/random data anymore so I wouldn't call the controller method that generated this ViewBag. Is there a way to retain this value without having some private variable in my controller? Some nice way that MVC/Razor does it?
Option 1:
Pass the value of "ViewBag.Something" to the Controller by using route Values:
#Html.ActionLink("ButtonText", "ActionName", new { Something = #ViewBag.Something })
Option 2:
You can use TempData.
public ActionResult Index()
{
var Something = "YOURVALUE";
TempData["Something"] = Something;
.......
}
public ActionResult OtherAction()
{
var Something = TempData["Something "];
...........
}
Passing State Between Action Methods
Action methods might have to pass data to another action, such as if an error occurs when a form is being posted, or if the method must redirect to additional methods, as might occur when the user is directed to a login view and then back to the original action method.
An action method can store data in the controller's TempDataDictionary object before it calls the controller's RedirectToAction method to invoke the next action. The TempData property value is stored in session state. Any action method that is called after the TempDataDictionary value is set can get values from the object and then process or display them. The value of TempData persists until it is read or until the session times out. Persisting TempData in this way enables scenarios such as redirection, because the values in TempData are available beyond a single request.
In the get, set up a model, set it dynamically and when return view() is being executed, do return view(model). Then in the view, set up a hidden field that can keep on passing the value needed. I chose to go this route because I don't have to worry about any server code to make this work on a post and I don't have to worry about any sessions.
Displaying message in viewbag after posting (I user this method)
ActionResult SubmitUser(){
ViewBag.Msg =TempData["Msg"];
return view();
}
[HtttpPost]
ActionResult SubmitUser(){
TempData["Msg"] ="Submitted Successfully"];
return view();
}
The Value is send to get method..
I have a controller action UpdateCustomer(CustomerDto customer) that returns a PartialViewResult with a model that is also a CustomerDto:
[HttpPost]
public PartialViewResult UpdateCustomer(CustomerDto customer)
{
CustomerDto updatedCustomer = _customerService.UpdateCustomer(customer);
updatedCustomer.Name = "NotThePostedName";
return PartialView("CustomerData", updatedCustomer);
}
In my view, I have the following line:
#Html.TextBoxFor(model => model.Name)
So far, so good. In my view I do an asynchronous post to this action method, the model binder does its work and I can update a customer in the database. Then I want to render the updated customer to the client. For example, I'd like to change the customer name in my controller. However, what gets rendered is always the properties from the posted customer, not the properties from updatedCustomer.
I decided to include the MVC3 source code in my project to see what really happens. It appears to be a feature (bug?) of MVC3 that it always takes the value from ViewData.ModelState instead of the value from ViewData.Model.
This happens at lines 366-367 of System.Web.Mvc.Html.InputExtensions:
string attemptedValue =
(string) htmlHelper.GetModelStateValue(fullName, typeof(string));
tagBuilder.MergeAttribute("value",
attemptedValue ?? ((useViewData)
? htmlHelper.EvalString(fullName)
: valueParameter), isExplicitValue);
As you can see, attemptedValue comes from ModelState. It contains the old value for CustomerDto.Name (the value that was posted to the controller action).
If this is a feature, why does it work this way? And is there a way to work around it? I would expect that if I update my model, the update gets rendered, not the old value I posted.
Well yes it's a feature (ModelState is always checked before actual Model), you can clear the ModelState, or update just the value you need:
ModelState["Name"].Value = updatedCustomer.Name;