Use ViewModels to manage data & organize code in ASP.NET MVC applications
Haritha April 19, at 1: The View is usually not unit tested unless you use Robolectric so the fewer lines of code the better. Wouldn't this not map properly to the controller that was accepting the form? For a fuller explanation, read Simple Dialog Service in Silverlight. It supports both WPF and Silverlight projects.
NerdDinner Step 6: ViewData and ViewModel
DropDownList helper method above takes two parameters. One of the defining characteristics of the MVC pattern is the strict "separation of concerns" it helps enforce between the different components of an application. ViewModel Interaction with Model and View. If you having any problem let me know. B'cos the ViewModel is the best place to do those kind of Field validations. Custom-shaped ViewModel classes can be used both to pass data from controllers to views to render, as well as to help handle form data posted back to a controller's action method. Nice , superb clean explanation with guide.
How to make secure this form Thanks for your great post. I have problem with drodownlist In Create. SelectedValue , new SelectList Model. ProductCategories , "Value", "Text" or this: ProductCategory, new SelectList Model. ProductCategories , "Value", "Text". Hi Enes, You're warmly welcome.
It depends the way you declare your VM. So if you follow the way which I showed above,you can use it as below with default value. Please explain this given in Controller.. Hi Rahul, Those are repository methods which I used for retrieve data. I have updated my post above for those details under 'Repository Methods'. Great article, I do have question on the Model. If I am applying this ViewModel and use entity framework.
Should the product class has the ProductCategoryId? It depends on according to the table structure of your app.
In my case it has 1: M relationship with the Product and ProductCategory tables. So I maintained the ProductCategory as a Traversal property on above example. But the problem is then you unable to validate Product fields by using Field validate attributes such as Required. B'cos the ViewModel is the best place to do those kind of Field validations. When you return RedirectToAction, it goes to get method where it creates a new viewmodel object. I tried doing in that way, but the property contents have been changed.
In the above example, I set property1 to someValue in post method. When I redirect to get method, the property has been changed to some other value other than someValue. Can you please let me know the solution of my problem.
Sorry if I am not clear. Answer For Your Question: Hence you're redirecting to the Action method,You can use "TempData" with it. Please read this article for more info. Basically I'm using a partial view which contains my form and in my Edit and Create view I call this partial view.
I have around 5 similiar DropdownlistFor and these work well on create action but in edit doesn't, mainly i'm not getting unable to set the selected value.
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Thanks for your informative article. Thanks for your Feedback. What is a ViewModel. Why We Use ViewModel. If you need to pass more than one thing to a strongly-typed view which is best practice ,. This allows you to validate your ViewModel differently than your domain model for. Can be used to help shape and format data. ViewModel is the best place to do it.
The use of a ViewModel can make the interaction between model and view more simple. ViewModel Interaction with Model and View. In a folder called ViewModels that resides in the root of the project. In a separate project s as a service layer, for large applications that generate. Put only data that you'll render use in View in the ViewModel. The View should direct the properties of the ViewModel, this way it fits better for rendering.
Use a Mapper when ViewModels become Complex i. How to Use ValueInjecter? Let's Try with Simple Example. SelectedValue, new SelectList Model. I hope this helps to You. Comments and feedback greatly appreciated. Posted by Sampath Lokuge at Anonymous October 30, at Sampath Lokuge October 30, at Danilo Cecilia October 30, at 5: Sampath Lokuge October 30, at 5: Anonymous October 30, at 5: The easiest solution in my opinion is to abstract the dialog behind an interface and provide a callback for the response.
The view model can import the dialog, then based on some change in state or a command, trigger the dialog service. The callback will return the response and then the view can process accordingly. For a fuller explanation, read Simple Dialog Service in Silverlight. This is a very common problem to tackle: Another issue I see raised quite often is how to deal with global variables and configuration information.
Again, this is less an MVVM problem and more a general architecture consideration. In most cases, you can expose configuration with an interface IConfiguration and then wire up an implementation with your configuration values. Any viewmodel that requires the information simply imports the implementation, whether via MEF, Unity, or some other mechanism, and only one copy of the class is kept Singleton pattern, although most likely managed by the container and not the class itself.
One point of confusion with Silverlight is that it forces service calls to be asynchronous. This can seem strange when building a viewmodel: Typically, this is managed by registered to an event when the process is complete, and binding the results. I prefer to hide the implementation details of the events behind a simple Action function. Sometimes you may have a more complex workflow that requires multiple asynchronous calls to execute and complete prior to continuing.
If that is the case, you might want to look into a mechanism for making it easy to code and read the sequential workflow. This post will help you understand one solution using coroutines, and this post describes how to use an existing robust framework to manage those calls with thread safety, error handling, and more.
I would argue it is certain implementations that have this issue, not the pattern itself. The solution is often to page the data, but I find many people approach the problem incorrectly. For some reason, developers want to insist paging is a function of the database and should be isolated to the data access layer.
In the most primitive form, you can create a collection that grows as the user pages. If your data is small, you might pull a very large collection and keep it in the Silverlight client, but use a virtualized panel to display the information the problem with some panels is that they create a control for every bound data element, which can crush performance — virtualized panels only create enough controls to fill the visible window on the screen. These queries contain extension methods that allow you to grab only the first few items in a list, rather than fetching the full list at once.
The framework also provides helper classes like the PagedCollectionView to help filter, sort, and page data. It does stress separation of concerns, which is nice. I would suggest that if you are spending days writing something just to avoid minutes of code-behind, your approach is wrong.
It is not required for Silverlight or WPF. I believe that line-of-business, data-driven, and forms-based applications are prime candidates for MVVM. Games, entertainment websites, paint programs, and others may not make sense. Be sure you are using the right tool for the right job. MVVM is not supposed to slow you down! All new patterns and frameworks come with a learning curve. The pattern is useful when it accelerates development, improves stability and performance, reduces risk, and so forth.
Now, what are your thoughts and comments? Jump to Appendix A: Jump to Appendix B: A very special thanks to the community members who took time out of their busy schedules to review and provide preliminary feedback and suggestions for this article: This software architecture pattern was first described in the context of Smalltalk at Xerox in This pattern builds on MVC but places special constraints on the controller, now called the presenter.
A general overview looks like this:. Martin Fowler describes this pattern with two flavors: Here is how Microsoft describes: In , Martin Fowler published his description of the Presentation Model. The summary is quite succinct: There are a number of out of the box frameworks that exist which implement MVVM. In no particular order:. This is a very popular toolkit that contains support out of the box for base viewmodels, commands, messaging, and project templates to get started.
It supports both WPF and Silverlight projects. The stated goals for this framework are to enable concise declarative specification of user interfaces, enable easier separation of view and code, and provide a lean framework.
Caliburn is a popular viewmodel-first framework that supports both WPF and Silverlight. More than just MVVM, however, it is a full application framework. The Controller base class exposes a "ViewData" dictionary property that can be used to pass additional data items from Controllers to Views.
For example, to support the scenario where we want to change the "Country" textbox within our Edit view from being an HTML textbox to a dropdownlist, we can update our Edit action method to pass in addition to a Dinner object a SelectList object that can be used as the model of a countries dropdownlist. The constructor of the SelectList above is accepting a list of counties to populate the drop-downlist with, as well as the currently selected value.
We can then update our Edit. DropDownList helper method instead of the Html. TextBox helper method we used previously:. DropDownList helper method above takes two parameters.
The first is the name of the HTML form element to output. The second is the "SelectList" model we passed via the ViewData dictionary. We are using the C "as" keyword to cast the type within the dictionary as a SelectList. Because we also render the Edit view template from the HTTP-POST Edit method in scenarios when errors occur , we'll want to make sure that we also update this method to add the SelectList to ViewData when the view template is rendered in error scenarios:.
The ViewData dictionary approach has the benefit of being fairly fast and easy to implement. Some developers don't like using string-based dictionaries, though, since typos can lead to errors that will not be caught at compile-time.
The un-typed ViewData dictionary also requires using the "as" operator or casting when using a strongly-typed language like C in a view template. An alternative approach that we could use is one often referred to as the "ViewModel" pattern. Our controller classes can then populate and pass these view-optimized classes to our view template to use.
This enables type-safety, compile-time checking, and editor intellisense within view templates. For example, to enable dinner form editing scenarios we can create a "DinnerFormViewModel" class like below that exposes two strongly-typed properties: We can then update our Edit action method to create the DinnerFormViewModel using the Dinner object we retrieve from our repository, and then pass it to our view template:.
We'll then update our view template so that it expects a "DinnerFormViewModel" instead of a "Dinner" object by changing the "inherits" attribute at the top of the edit.
Bilder: single view multiple viewmodels
Sampath Lokuge November 8, at 8:
You can download the source code for this example here. Before returning the model values again we have to re populate the items otherwise we have to use ViewBag. Anonymous November 7, at
Sampath Lokuge July 5, at Now, what are your thoughts single view multiple viewmodels comments? All new patterns and frameworks come multpile a learning curve. Sending a ViewModel to the view for rendering will work the same as when dealing with a model. Andy Mai December 22, at Almost no dependencies Minimum dependencies:
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