ViewModels or ViewBag?

Question

I'm fairly new to MVC4, EF5 and ASP.Net, and I don't seem to be able to find a good answer anywhere.

Basically, Should everything be done through the viewmodel or is it Ok to also incorporate viewbag?

Say I have a method which populates a drop down list, and I am using a viewmodel to represent the output for the view.

Am I ok to use Viewbag.DropDown = PopulateDropdown(); or would it be better to incorporate this into the ViewModel, by creating a property to hold the List<SelectListItem> created by PopulateDropdown(); ?

I know how handy ViewBag is, but I'm yet to see any solid reason as to not use it? If anyone could also offer me some more insight, that would be fantastic.

Answer 1

Basically, Should everything be done through the viewmodel or is it Ok to also incorporate viewbag?

Everything should be done inside a view model. That's what a view model is. A class that you specifically define to meet the requirements of your view. Don't mix ViewBags with ViewModels. It is no longer clear for the view where is the information coming from. Either use only a view model (approach that I recommend) or only use ViewBags. But don't mix the 2.

So in your particular example you would have a property on your view model which is of type IENumerable<SelectListItem> and inside your view you will use the strongly typed version of the Html.DropDownListFor helper to bind to the model:

@Html.DropDownListFor(x => x.ProductId, Model.Products) 

Obviously those are only my 2 cents. Other people will say that mixing ViewModels and ViewBags is fine and I respect their opinion.

Answer 2

Prefer ViewModels over the ViewBag wherever you can. Create Strongly typed views. It makes your code cleaner, less fragile, less error-prone, and easy to maintain.

ViewBags are just dictionaries of dynamically typed objects so you lose:

• Compile time checking
• The ability to refactor with confidence (you lose the support of the tools)
• IDE support - such as the ability to navigate to all usages
• Intellisense

For bonus points making extensive use of the ViewBag also misses the point of using the MVC pattern

I get the impression ViewBags were created to solve an edge-case problem in asp.net and people use them instead of creating view models as was originally intended in the design of the platform, to the detriment of their work.

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with thanks to Why not to use ViewBag heavily?