In my controller I have the following:
ViewBag.VendorName = vendorname;
In my View I have the following:
#Html.TextBox("VendorName")
It appears that the TextBox VendorName is being populated with the content of ViewBag.VendorName.
This is what I want but didn't know that from a ViewBag you can directly populate a TextBox.
Is this expected and why does this happen?
According to Steve Sanderson in Pro MVC:
HTML helper methods populate their value from the following places (in this order):
ViewData.ModelState["VendorName"].Value.RawValue
For string based helpers, the value parameter passed to the helper method, or if you didn't supply one, then ViewData.Eval["VendorName"] (and ViewBag.VendorName as you're seeing here)
For strongly typed helpers, the corresponding property value on your Model object
Related
I have an dot net 5.0 mvc page which takes a model object (ClassFoo) which when constructed generates an instance of (classBar). ClassBar has various properties (FieldA, FieldB, FieldC) all are strings.
The Views content is all in a form and the form's input fields are all from ClassFoo.ClassBar's various properties. Initially, when the page is accessed, all form input values are empty. However when I put data into them and then submit the form, the form values are still there when the page loads. However I don't understand why this is because I'm explicitly creating a new model during the controller operation but I am not actually populating the Model.ClassBar with the content from the post before I return model to the View for generation.
What I would expect is that all of the form fields would be empty however that is not the case. I know if asp.net the form values are stored and restored automatically but I didn't think that happened in mvc.
After looking into ModelState recommended by Nick Albrech in the comments I reviewed the hint associated w/ the HtmlHelper.TextBoxFor() which states the following:
... Adds a "value" attribute to the element containing the first non-null value found in: the ActionContext.ModelState entry with full name, or the expression evaluated against ViewDataDictionary.Model. See [IHtmlHelper.NameFor] for more information about a "full name".
So effectively what's happening is similar to what I thought asp.net mvc wasn't doing in that it populates the ModelState from a get/post request with the name and values of the form being submitted. Then based on the use of these helper functions (and also asp-for attributes used in razor views views), it either provides values from the saved model state form values OR the model passed to the view. Note: this does not seem to work if you set the value of an input element = #Model.[someProperty]
The take away from this is that you do not necessarily need to update your model object with content from the previous form submit in order to have the page populate the form contents back to the screen. Allow asp.net mvc to do the manual tasks by making use of these razor helpers.
Shoutout to Nick for the assist on this one. A solid member of the stackOverflow community.
I'm working on my first MVC application, still figuring it all out.
I have a viewmodel which, at this point, is identical to my domain object. My controller builds the viewmodel and passes it to a view. The view only displays a some of the properties because I don't want primary and/or foreign keys displayed for the user yet, in the case of a primary key, I need to have the data in order to update / delete the database.
It appears that unless I use a viewmodel property in the view, it is set to default values (0 for numeric value types and null for reference types) when I pass the viewmodel back. Is this correct behavior?
I confirmed the viewmodel passed to the Edit view does contain all the properties (as I would expect).
The question - Once a view is rendered, what happens to the viewmodel? If my viewmodel contains properties that are not used in the view, do their values just disappear? For example, when I click the Edit actionlink to fire the Edit action on the controller, the viewmodel that gets passed to the action does not contain any properties unless they are visible on the screen. Why?
BTW, this is ASP.NET MVC 4 RC.
It appears that unless I use a viewmodel property in the view, it is
set to default values (0 for numeric value types and null for
reference types) when I pass the viewmodel back. Is this correct
behavior?
Yes, when you invoke a controller action you need to pass all the properties that you want to be bound in the request. So for example if you are using a html <form> to call the action you need to use input fields. You could use hidden fields but they must be present, otherwise nothing is sent to the controller action
The question - Once a view is rendered, what happens to the viewmodel?
It falls out of scope and is eligible for garbage collected.
If my viewmodel contains properties that are not used in the view, do their values just disappear?
Absolutely. But even if you use those properties inside the view they disappear. For example if you only display the values inside the view but do not use input fields to send them back to the server when the form is submitted they will be gone as well.
For example, when I click the Edit actionlink to fire the Edit action
on the controller, the viewmodel that gets passed to the action does
not contain any properties unless they are visible on the screen. Why?
Because the view model no longer exists. It's gone and garbage collected. That's how the HTTP protocol works. It's stateless. Nothing is persisted between the requests. You will have to include whatever properties you want to be populated in the request either as POST form values or as query string parameters if you are using action links or whatever.
If the user is not supposed to modify those values inside the view you could then simply pass an id to the controller action which will allow for this controller action to retrieve the model from wherever it is stored (a database or something) using this id.
If your properties are in any helper methods which generates the input HTML element inside a form, It will be available in your HTTPost action method when you submit the form. If you are simply displaying it in a div/span , it is not going to get you the property values. That is how MVC model binding works.
Expect the values in your HttpPOST action if you use these HTML helpers
#Html.TextBoxFor
#Html.DropDownFor
#Html.EditorFor
#Html.HiddenFor
Dont expect the values if you use these
#Html.DisplayFor
I have uploaded my code to pastebin, this is the link:
http://pastebin.com/wBu9PP2x
When i submit a form, the Lists that i use are not bound to my ViewModel.
But when i send the ViewModel to the view, it renders fine using EditorFor. I have read that when using EditorTemplates, it is supposed to name the List appropriately so that they are bound to the ViewModel automatically upon postback.
The HTML output can be seen here:
http://pastebin.com/5KeyNXWC
Notice that the ViewModel derives from ShowQuestionViewModel, which contains some strings. These strings get bound perfectly.
This is the tutorial i have been following:
http://jarrettmeyer.com/post/2995732471/nested-collection-models-in-asp-net-mvc-3
In the tutorial, the MVC framework knows how to bind lists inside of a ViewModel.
Here are some debugger outputs:
Controller takes ShowQuestionViewModel as parameter:
http://imageshack.us/photo/my-images/803/debug.jpg
Controller takes FormCollection as parameter:
http://imageshack.us/photo/my-images/542/formcollection.png
Different Controller that takes a List and FormCollection as parameter:
http://imageshack.us/photo/my-images/685/listtest.png
Dont give up on me guys!!
Thanks!
Solution
I have found this solutin myself. I forgot to use Properties for the rows and columns list in the ShowMatrixQuestionViewModel. Also, the ActionController wont bind without TryUpdateModel() so thanks to #Adam Tuliper as well as the rest.
Since you mentioned lists are you sure your model Upon postback contains all of the expected items? Also remembe the HTML helpers will use modelstate to bind data from as well if you are showing data after a post and not redirecting.
In our asp.net mvc I've created view with two partial views inside.
That view accepts model of some type, for example Customer.
First partial view doesn't have model because it is search form with empty field.
Second form is form with populated fields.
What I found out that on first view, if I have called input fields like properties in model and if I don't provide value for them, mvc implicitly binds values from model to the fields.
First I was thinking is some of kind of mistake, but then I've expiremented little bit with a code:
-I've added native input element with id and name called the same like model, input field is empty in browser
-If I try the same thing with Html.TextBox helper and don't provide value, mvc gets that value from my model object(by name of property/field) and in browser that field is populated.
Is this a bug or am I doing something wrong?
Thanx
That's by design.
I'd recomend reading:
http://asp.net/mvc
http://weblogs.asp.net/scottgu/archive/tags/MVC/default.aspx
and last but not least:
http://channel9.msdn.com/Events/MIX
especially mix10 has a tonn of sessions about mvc
all are good read and watch (-:
That is by design. If you send a model to a view and you're using the HTML input Helpers that come with ASP.NET MVC, they'll implicitly populate themselves from the model.
This is helpful in many situations. If you don't want this behavior, you can always NOT use the helpers or write your own simple helpers.
I am using MVC 3 w/ Razor and using the new dynamic ViewBag property. I would like to use the ViewBag property with the EditorFor/LabelFor Html helpers but can't figure out the syntax.
The View does have a #model set, but the object I am trying to use is not part of that model. I am aware I can create a ViewModel but that is not what I am after.
Can anyone help?
Controller:
var myModel= _repo.GetModel(id);
var newComment = new Comment();
ViewBag.NewComment = newComment;
return View(myModel);
View:
#model Models.MyModel
#(Html.EditorFor(ViewBag.NewComment.Comment))
I haven't tried it, but this should work I think.
#(EditorFor(m => ViewBag.NewComment)
It is possible to use a Linq-to-SQL syntax, but use a completely different object on the right side.
Not knowing what your Comment Model looks like, my gut reaction would be to just do:
#Html.EditorFor(ViewBag.NewComment)
However, because ViewBag is dynamic, you may need to cast NewComment before you use it, in order to get the EditorFor magic.
#Html.EditorFor(ViewBag.NewComment as Comment)
Update
Strike that, EditorFor can only accept an Expression as a parameter, and that Expression must return a property of the page model. I don't think EditorFor or EditorForModel are going to be of any use to you if you don't want to use a ViewModel. Have you considered switching the roles of whatever it is you're using the Model for, with that of the ViewBag?
If for some reason I need to use ViewData to pass the model into my view I do the following to allow for the Html.DisplayFor() helpers.
In the views code block I cast the ViewData model object to its underlying type
var newCommentModel = ( NewComment )ViewBag.NewComment;
Then I assign the following expression to the helper using the strong-typed reference
#Html.DisplayFor( model => newCommentModel )
The expression tree now contains a strongly-typed model and the DisplayTemplate is correctly displayed.