In my ASP.NET MVC 3 app I have a page where, after its form is submitted I need to change a value from the form. If I do it in the ViewModel it has no effect, I have to do it use ModelState["Field"].Value.
The thing is that I actually have a lot of work I have to do on the ViewModel when the pages loads AND after the POST. So I have a method which receives the ViewModel and do all that work. But, as I said, after the POST, modifying the ViewModel object is useless. Why is that? The method on the controller is returning View(viewModel);. Shouldn't the view use the ViewModel values?
I'd like to understand why is useless to modify the ViewModel and also know if there is some method in the ModelState which "refresh" the fields values throw a ViewModel object.
Here is my controllers code:
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Index(MyViewModel viewModel)
{
try
{
if (ModelState.IsValid)
//Do stuff and redirect
}
catch(Exception ex)
{
//Log and add error to the ModelState
}
someMethodWhichDoesALotOfThingsInTheViewModel(viewModel);
return View(viewModel);
}
I think the rest of the code is unnecessary, if anyone think it would help let me know!
Update
I don't want to lose any errors, not even those of the fields changed in the ViewModel. A good example would be a captcha, if the users makes any error in the form (only with the captcha field or only with any other fields and not with the captcha) I want to show him all his errors and also update the captcha. It makes no sense to render the form with the old captcha value inserted so I want to blank that field.
Update 2
I've opted to put #Value = Model.PropertyInViewModel in the HTML Attributes of each Html.TextBoxFor. But I'd prefer to avoid that nasty work so if someone comes out with any better solution please let me know.
The following will work:
ModelState.Remove("MyProperty");
viewModel.MyProperty = "new value";
You need to remove it from the model state because HTML helpers first look in there when binding their value.
All I could came out with is to add #Value = Model.PropertyInViewModel to each Html.TextBoxFor that is going to be modified in the ViewModel.
Another way, as #Darin Dimitrov said, would be to make my own helpers.
If you decide to remove modelstate values to prevent round-tripping take a look at this RemoveFor() extension method I made to remove ModelState errors without magic strings.
Related
I'm new to MVC and I'm trying to make my first Ajax page, PartialView.
What I have is an action that looks like this
[HttpGet]
public PartialViewResult MainContent()
{
return PartialView(new ClockingModel());
}
[HttpPost]
public PartialViewResult MainContent(SingleClocking SingleClocking)
{
// update logic
return PartialView(myClockingModel);
}
What I'm finding is that the view renders, I enter some data and it posts back correctly. My partial view includes a select:
#Html.DropDownListFor(x => x.SingleClocking.InWhen, new SelectList(Model.DropDownValues, Model.DefaultValue))
The select shows the value that I changed on the GUI, not the new DefaultValue?
If this was plain Asp.Net I would assume this was because of postback data or viewstate but MVC doesn't use either of these?
I can see the view being returned via fiddler, it shows the select with the value as per the client, not the value I expected to see via the server.
I'm sure I'm just missing something simple here, any hints?
Also, could I look at the value of the View on the server? This won't work but something like: string viewText = PartialView(myClockingModel);
p.s. I don't think it's caching, I tried switching that off with an attribute
And even though I searched for a while before asking this I finally found the answer.
I feel a bit better knowing that Rick Strahl had the same confusion.
Posting as an answer for others to find
Long story short, this is by design, the blog is worth reading
http://weblog.west-wind.com/posts/2012/Apr/20/ASPNET-MVC-Postbacks-and-HtmlHelper-Controls-ignoring-Model-Changes
I'm working on an ASP.NET MVC2 app. I've come to realize a very surprising, yet amazing thing that MVC does behind the scenes having to do with the ModelState and model binding. I have a ViewModel which has a whole bunch of data - some fields being part of a form while others are simply part of the UI. On HttpPost, my Action method uses the DefaultModelBinder which attempts to bind the whole model, but only fields which were part of the form are successfully deserialized - all others remain null. That's fine and understandable. If the ModelState is invalid, I need to refresh the model from the db and bind those particular form fields before returning to the same edit view to display those associated ModelState validation errors.
Here's where my amazement and curiosity comes. It was my assumption that in order for me to bind the form fields with the refreshed model, I needed to make a call to either UpdateModel() or TryUpdateModel<>(), passing in the newly refreshed model. For example:
[HttpPost]
public ActionResult EditDetail(EditDetailItemModel model)
{
if (model.IsValid)
{
// Save the results to the db
return RedirectToAction(...)
}
// Can't simply "return View(model)". Not all fields in EditDetailItemModel
// were part of the form - thus they returned null. Have to refresh
// model from the db.
var refreshedModel = RefreshModelFromDB();
// Is this line necessary?????
TryUpdateModel<EditDetailItemModel>(refreshedModel);
return View(refreshedModel);
}
But, what I found was that if I simply returned refreshedModel to the view WITHOUT making a call to TryUpdateModel<>(), the refreshed model was automatically bound with the form field values posted!! Hence, the TryUpdateModel<>() is not needed here!
The only way I can make any sense of it is that since the ModelState is in an invalid state, once I returned the view with the refreshed model, the "MVC rendering engine" looped through the ModelState errors and bound those property values with my refreshed model. That is simply AWESOME! But, I want proof as to this assumption. I can't find documentation regarding this anywhere on the web. Can anyone either confirm my hypothesis of WHY/HOW this AWESOME auto binding behavior is occuring and/or educate me as to why/how it's happening, hopefully backed up with some online documentation links so I understand more fully what's going on under the covers?
public ActionResult EditDetail(EditDetailItemModel model)
That line will perform model binding. Think of ActionMethod parameters as always being populated by a call to UpdateModel.
You are not seeing refreshedModel's values in the view, you are seeing the ModelState entries and values from EditDetailItemModel.
In asp.net MVC application we have mechanism where, when we submit
a form and if there is any problem with the values (validation fails),
the form is displayed back maintaining old values. How does it happen ?
Where are these values kept ? or they collected from FormCollection.
Help will be apprititated.
Regards
Parminder
It really depends on how you set up your Controller Actions and your Views, because ASP.NET MVC looks in multiple places for the values.
Your assumption that it uses the FormCollection is kind of wrong, since the FormCollection is something that your controller Action takes in as a parameter and is totally separate from your View, where the values actually end up being displayed.
In 1.0, by default, the Edit template for views uses the 2nd parameter on most of the HtmlHelpers, like:
<%=Html.Textbox("Title", Model.ID)%>
This would have the old value pulled from the bound model object. So if you explicitly fail validation and return a View(object), the values would be pulled from that object. Still, if you are explicitly failing validation like:
if (ModelState.IsValid == false)
{
return View();
}
Then the HtmlHelper code will likely result in an error, because no Model was bound.
If you completely leave off the 2nd parameter, like:
<%=Html.Textbox("Title")%>
The value will be pulled from the post (Request.Form) values.
One way to do it is to use ModelState.AddModelError
A good tutorial on MVC Error handling can be found here
You can do that by returning the view with tha data
if (ModelState.IsValid == false)
{
return View(X);
}
X is the data u need to return
Is it possible to disable a certain action parameter from retaining its value across requests?
[HttpPost]
public ActionResult MyAction(string value1, string value2)
{
if(value1=="hi")
ModelState.AddModelError("value1", "Can't have hi");
//do stuff
if(ModelState.IsValid)
return RedirectToAction("Finish");
else
return View()
}
[HttpGet]
public ActionResult MyAction()
{
return View()
}
The view consists of a simple form with two input boxes (value1 and value2). Once submitted and validation fails, the view is returned. I want to always have the value of the textbox in the view to be empty.
The value for the textbox "value1" is retained if the the model is invalidated.
I tried to declare the textbox as <%= Html.TextBox("value1", null) %> but the value is still retained. I also tried to use [Bind(Exclude="value1")] but that dosen't work on a single variable.
Update 2:
I'm doing this for a textbox that is used for Captcha (custom solution) input. I want the textbox to be cleared any time the page is loaded, but I want validation to remain.
Try calling
ModelState["value1"].Value
= new ValueProviderResult(null, string.Empty, CultureInfo.InvariantCulture);
before you return the view from within your controller action.
What this does is keep all the errors associated with the key "value1", but replaces the value with an empty value.
What are you doing that's causing it to be retained? There isn't anything like ViewState in MVC that will persist a value over multiple requests unless you're writing code or using form fields to make it do so.
What does the view look like? Is this action method being called via GET or POST? What's the "do stuff" contained in your method?
Edit: You're still showing //do stuff in your example code. Does that stuff contain any references to ViewData? Your question is about binding, but I don't see any binding happening. Maybe this is beyond my understanding.
Edit 2: Glad Phil saw this one! The original question didn't mention the ModelState.
I'm writing a simple blogging platform with ASP.NET MVC. My question is regarding forms contained in partial views and handling the response, validation errors or success, from the controller.
I have a blog post item view which has an associated controller that returns a post for a given URL. Embedded in this view is a partial view containing a form for submitting comments on the post. The partial view form submits to a separate controller that handles adding comments. Inside the add comment action I perform validation and add errors to the ModelState object.
The problem is that I have to return a RedirectResult on the partial view action so that the user is returned to the originating post item, which means that I lose the ModelState object or any success messages I want to return.
I've seen people mention the use of TempData to pass validation or success information back to the original view, but to me this sounds a bit hackish. Is this really the solution? If so can anyone recommend a good example of its usage? If not, is this a sign of bigger problems in my chosen architecture?
I have used the PRG Pattern in the past give it a try
Use PRG Pattern for Data Modification
You can have the add comment action call the view post action...
Something like this I guess:
public class PostController
{
... blah ...
public ActionResult ViewPost(int postId)
{
Post post = PostRepository.GetPost(postId);
return View("ViewPost", post);
}
public ActionResult AddComment(int postId, string comment, string otherInfo)
{
//Validate stuff, setting modelstate etc
//If it isn't valid, return the same post view (modelstate will stay)
if (!ModelState.IsValid)
return this.ViewPost(postId);
//If it is valid then we want to save it and follow PRG pattern
PostRepository.Save(newValidComment);
TempData["Message"] = "Thanks for your comment!";
return RedirectToAction("ViewPost", new {id = postId});
}
}
Or a variation of the same concept...
HTHs,
Charles
Have you considered using the Ajax libraries to just post that area of the page? That way you wouldn't need to redirect.