Because of the confusion between all the info that is out there about mvc from all the preview releases and the one official release I am very confused how to deal with viewusercontrols.
So once and for all, tell me how to implement this example:
I have a list of upcoming events that needs to be displayed on several pages of my website. Therefore I have put a new ViewUserControl (ListEvents.ascx) inside my Views\Shared folder.
I am requesting this ListEvents.ascx to render on my Home/Index view like this:
<p>
Here's a list of events:
<% Html.RenderPartial("ListEvents");%>
</p>
How would I go about passing my model to this viewusercontrol? I know I can do this:
<p>
Here's a list of events:
<% Html.RenderPartial("ListEvents", (new Model.Services.EventService(null)).ListEvents());%>
</p>
But that doesn't seem like a very smart thing to do, creating a new model from inside a view?! Or am I wrong here? I can't even pass any validationstate, hence the null parameter.
So an alternative option is to store this data into the ViewData[] member, but my viewusercontrol is not supposed to be dependant on the ViewData of it's parent!
I'm sure there is a very simple answer to this, please share as I'm done browsing the web for this problem.
Thanks!
Simple Answer:
A viewusercontrol should always receive it's model from the View in which it resides. Working around this, like by adding a codebehind file to a viewusercontrol, would break the MVC pattern.
By default, the same model as the page will be used. If you want to provide a model to each instance of RenderPartial, your situation is probably like rendering several entries in a blog application. You could fetch each model from a collection in your page model and pass it to the user control like this:
foreach (var post in Model.Entries) {
Html.RenderPartial("PostTemplate", post);
}
Related
Question background:
I have a two page MVC 4 web app. The first page's view currently has its data manually typed into the View as its static i.e nothing is being passed to the View from its associated Controller method, as shown:
Index controller method:
Public ActionResult Index()
{
return View();
}
Index.cshtml View:
<div class="titleHeader">Welcome To This Test Example</div>
Best practice:
Is the above example OK to use, or should I generate a ViewModel object on the Index controller, populate the static data then return it to the View? As Shown:
Index Controller Index method with ViewModel:
Public ActionResult Index()
{
HomePageVM homepageVM = new HomePageVM
{
WelcomeMessage = "Welcome To This Test Example";
};
return View(homepageVM);
}
Index.cshtml now bound to the HomePageVM ViewModel:
#model TestPage.Models.HomePageVM
<div class="titleHeader">#Model.WelcomeMessage</div>
I think (opinion), it's best to use Resource files for static data.
With these Resource file you will be able to easily port to a multi language website.
Basically you'll need to create resx files, make the entries public.
In your cshtml you can access it by:
<div class="titleHeader">#Resources.WelcomeMessage</div>
Depending on the UIThread's culture info it is able to select the appropriate language.
You can find a tutorial here:
http://www.codeproject.com/Articles/778040/Beginners-Tutorial-on-Globalization-and-Localizati
As for your options:
1) There is really no need to create a ViewModel for static data unless you'll expect it to be dynamic in the future (although it's bad habit to develop now for future requirements).
2) Hard coded strings in the cshtml, it possible, but not suited for multi-language. There is 1 benefit I would like to mention: it's easier for non-developers to alter the html.
Based on the principle of not gold plating your code.
You don't need the view model (right now) so don't add it. If you want a view model later then it's simple to add one. Your goal should be to create the simplest solution possible. For me that means the view model (or any other solution that's not pure HTML) only add's unnecessary complexity.
The answer from stefan about resources again seems gold plating to me. It's based on the:
will be able to easily port to a multi language website.
Is your site multi language? Is it ever likely to be? If no, this is gold-plating.
I am not really a code guru but:
Why use viewbag or even viewmodel when you just want to show one line of static text? You don't usually use calculator when you want to add 2 + 2 don't you ?
<div> seems fine to me in this one
I understand when I create a view, I shouldn't be putting any code in there besides html and the data from the model/controller, which is what I've done so far.
But lets say there is a snipped of dynamically generated html that can be used in multiple views, I'm guessing this would be a partial view that goes in the Shared folder in the project. But since it's a partial view, that has no absolute controller to handle it's propagation of dynamic data (from db), how would I call, and where would I code the propagation of data from the db into the view (or model?), if lets say the partial view was to dynamically render content for table.id=n, etc.
I'm fairly to new and working off a tutorial in .net, trying to figure out how to do this. Anyone know how it's done? Hope the question makes sense.
You can always define a model for the partial.
And you can render the partial from the container view passing a dinamically populated instance of its model:
<!-- index.cshtml -->
<h1>Feed Upload</h1>
<div id="uploader">
#Html.Partial("~/Views/Shared/Controls/_FileUploader.cshtml", new FileUploaderModel() { UploaderClassName = this.Model.UploaderClassName })
</div>
In this simple example I call the partial _FileUploader.cshtml from the index.cshtml using the #Html.Partial() method, passing a new model instance that specifies the UploaderClassName value.
Edit
The this.Model.UploaderClassName refers to the container's model and it is initialized inside the container's controller business. Of course the container's controller can run any data access logic to grab dynamic data from the db and pass them to the partial's model.
Have a look at MSDN, and at this article.
Assuming you are using the razor view engine, you can put an .cshtml file in the App_Code folder with helper functions.
The syntax is like this:
#helper FormatDate(DateTime date)
{
#date.ToShortDateString()
}
You call it like this (assuming the file is Utility.cshtml)
#Utility.FormatDate(Patient.DOB)
Because you can pass parameters to a helper, you can pass any type you need, including complex objects.
I recently published a nuget package to do this very thing. It's called Dynamic MVC.
http://dynamicmvc.com
You can look at the source code on codeplex.
https://dynamicmvc.codeplex.com
The way I did this was to use the ModelMetadata engine built into MVC to allow me get the value for any property in a weakly typed fashion. The ModelMetadata engine originally came from ASP.net Dynamic Data and was ported over to MVC in MVC2. It works great for this kind of situation.
We have a model (say, List<string>). The function that builds the list is non-deterministic and the output is needed to be referenced in both controller and the view during the lifetime of the request. Since it's per-request, it cannot be static or singleton.
It's a common structure and it can be referenced from any view or controller.
Since we can't access controller from the view (by principle, and we agree), we cannot keep it in the controller. We're currently keeping it in the ViewData dictionary and initialize it in the controller, or the view (if the controller didn't need it).
We think that using ViewData for this purpose may not be ideal since it's not created to be consumed by a controller in the first place. Is there a better way to share common per-request data between Controller and the View? If not we'll stick with ViewData.
There is HttpContext.Items dictionary but I'm not sure if it fits to this purpose.
the output is needed to be referenced in both controller and the view during the lifetime of the request
The way MVC works, the Action code in the Controller is executed, and the resulting data is passed to the view engine that draws the page using the info you passed either with the call to View(data) or in the ViewData dictionary.
I don't know what you are trying to do, but it sounds like it's more a problem of a bad approach than a technical one (I might be wrong, though).
Could you explain why you need the controller while the View is rendered? If you need any logic associated with the List (to process it or do anything with it) I would just create a new class that extends List<T>, add the logic to that class instead of the controller, and pass an object of that class to the View, either using View() or ViewData[].
What is exact thing you're trying to do?
Seems like you just asking about the way to pass some data from the Controller to the View which is rather trivial task. Just use ViewData, yes, or ViewBag in MVC3 case or use ViewModels.
Or there is somewhat special case? What does "referencing from Controller and from View" mean? Where the data is coming from? Usually the case is that Controller prepares data for the View and passes it as an ActionResult (or better, as a ViewModel). View should never take some data on its own bypassing the controller.
Controller action should always be called be first. If you have multiple controllers calling the same view/partial view then you should be refactoring the code to one method and call that.
ViewData is the solution to do this, if your really wanting "once access" type information then maybe TempData but ViewData is designed for this.
All my controllers are based off of a BaseController, to share properties between them and override OnActionExecuting to set some values based on the route.
I'm creating a BaseViewData class to do the same for all my view data.
At the moment I'm populating the view data like so (C#):
var viewData = new BaseViewData
{
Name = "someName",
Language = "aLanguage",
Category = "aCategoryName"
};
I do this in every action that requires the view data. Some of the properties are common, need to be set throughout every action. Is there a way to set some of the properties on a more global scale?
If I instantiate the BaseViewData class in the OnActionExecuting method on the BaseController, how do I access the BaseViewData properties from the action in the regular controllers (derived from the BaseController)?
Update in response to Dennis Palmer:
I'm essentially doing this because of a nagging issue I'm having with ViewData["lang"] not being populated randomly on some requests. ViewData["lang"] contains "en" if the language is English, and "ja" if it is Japanese (well, it's supposed to anyway). I populate ViewData["lang"] inside OnActionExecuting on the BaseController.
In my view, I make a call to some partial views based on the language:
<% Html.RenderPartial(ViewData["lang"] + "/SiteMenu"); %>
But I'm randomly getting errors thrown that state "Cannot find /SiteMenu", which points to the fact that ViewData["lang"] has no value. I just cannot find any reason why ViewData["lang"] would not get populated. So, I'm rewriting the site to use ONLY strongly typed view data (and setting some hard defaults). But if another method is better, I'll go that way.
Thank you!
I'm not sure I follow exactly what you're trying to do, but if your view is using values in the route to display certain information, it seems like adding your own extension methods for HtmlHelper would be a better way to go.
Are Name, Language and Category contained in your routes? If so, then HtmlHelper will have access to the route info and can determine what to display via the extension methods. What is the correlation between your routes and what your views need to know?
Update: Is lang part of your route? If so, then I would still contend that you could write an HtmlHelper extension method that looks at the route data directly and determines which partial view to render. That way your controller wouldn't even need to worry about setting the ViewData["lang"]. The view would always know how to render based on the route.
Update 2: I think dismissing use of an HtmlHelper extension method because it re-evaluates the route data might be a case of premature optimization. Your controller inheritance scheme sounds overly complex and you asked the question because the way you were setting ViewData was unreliable. I doubt that pulling the value from route data would be much, if any, less efficient than setting and reading from ViewData.
From your comment:
In the controller I use the lang value
to determine which view to show as
well.
That only makes me think that there are more pieces of your system that I'd need to see in order to give better advice. If you have separate views for each language then why does the view need to be told which language to use?
Another alternative to consider would be using nested master pages. You could have a single master page for your site layout and then a nested master page for each language that just contains a hard coded lang value.
Perhaps instead of this inheritance scheme you have, you can just use action filters to add the data you need.
Ok, I'm still getting the hang of asp.net and the MVC framework and converting my knowledge over from classic ASP and VB - so please be gentle.
I've got my first view (/home/details/X) functioning well thanks to previous help pointing me in the right direction, now I need to add data from multiple tables and queries/views to the MVC view (I hate that SQL and MVC both use the word view for different meanings).
I'm not looking for someone to write the answer for me (unless they're feeling really energetic), more so for someone to point me in the right direction of what I should be looking at and reading up on to understand it and do this myself.
My problem
There are multiple datasets which I need to display in this view, and each different data set has a proper PK/FK 1-M relationship established, and the resultant records would need to be looped through.
How I would have done this previously
In my classic ASP days, I would have just defined the SQL query at the head of the page where the data was to be used, with a select statement along the lines of:
SELECT * FROM query_name
WHERE query_uniquecolumnname = Request.QueryString("value")
Once that was done, you'd set the do while query_name NOT BOF/EOF up, then drop in the field names you wanted from that query and it was all done.
How do I acheive this now?
So, fast forwarding from my classic ASP knowledge, how do I acheive the same outcome with MVC?
The tables/views I wish to use are already defined within my data model (and the relationships are showing up in there which I would assume is a plus), I just need to work out how I could call these within the page and use the ID of the record being displayed in the Details view to ensure only related data is displayed.
Thanks in advance
The concept you are looking for is called a ViewModel. Essentially this is a custom class that you write that contains all the data that would be used in your view. So it is responsible for amalgamating all the data from the different tables and exposing it as properties. If you're using a data access layer, this is often as simple as bringing a few entities together. If you're using raw SQL to do it, then you would execute your queries when the properties were accessed.
Then you would make your View inherit from the ViewModel, like so:
<%# Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master"
Inherits="System.Web.Mvc.ViewPage<MvcApplication1.Models.MyViewModel>" %>
Now in your View, you can access all the different properties of your object simply by writing statements like:
<%= Html.TextBox("MyProperty", Model.MyProperty) %>
To construct your view from your controller, create a new instance of your class (MyViewModel), pass it the ID of the details record that you need, and the logic in your class will take care of getting the right data. Then return your view from your controller like normal.
var myDetailsModel = new MyViewModel(detailsID);
return View(myDetailsModel);
I would recommend reading this primer on ASP.NET MVC
http://weblogs.asp.net/scottgu/archive/2009/04/28/free-asp-net-mvc-nerddinner-tutorial-now-in-html.aspx
It covers most basic scenarios you'll need to get up and running.
If however you want to combine multiple resultsets into one, and then return it as a view, you should create a custom object, and map the resultset to it, then you can bind against your custom object in the view.
When I need to display multiple things like this on a web page, I use typically use RenderAction to do it.
RenderAction allows you to use a controller method dedicated to that particular part of the view (a subview, in effect), so you can pass a single data set of strongly-typed data to that "subview".
RenderAction is in the Microsoft.Web.Mvc ("futures") assembly.
If you are new at all of this, I apologize; this is a bit bleeding edge, but you're going to need to know it anyway. Be sure to check out the NerdDinner tutorial first.
http://www.andreas-schlapsi.com/2008/11/01/renderaction-and-subcontrollers-in-aspnet-mvc/
http://davidhayden.com/blog/dave/archive/2009/04/04/...