17 Nov 2014
ASP.NET MVC is a very powerful, yet quite complex (if not complicated) web development framework. There’s a heaps of various namespaces, classes and functions. It’s bloody hard to figure out which particular class or function overload you need to use for your specific task.
This article is one of the ‘DropDownList series’ articles that should help you in dealing with DropDownList / SelectList / SelectListItem related problems. Check out other DropDownList articles here:
Seemingly simple things, such as creating a humble drop down list with elements from a given enum can be quite perplexing, and lots of people get stuck there, not even knowing how to start. In this article I will show in just a few simple steps how to do the following:
Check out my previous article Using simple Drop Down Lists in ASP.NET MVC for the detailed breakdown on how to create a simple drop down list on a form, populate it with values from a controller, send selected value back and render the drop down with the value selected.
Let’s put together a fictitious user profile page which has text boxes for First and Last names and Industry selection drop down list. It’s going to look like this:
Contents of the drop down list will be based on the following enum:
If you are amongst the more lucky ones and happen to use 5.1 or a later version of the ASP.NET MVC,
there’s a really neat shortcut – check out this
EnumDropDownListFor helper function. (By the
way, isn’t that wonderful how cryptic Microsoft’s doco is? Fear not though.)
Here’s all you really need to do to put a drop down list on a form:
Similarly to the simple drop down list, you get user’s selection in the
on POST. The helper function will also do all the heavy lifting to create proper
<select> tag, which will have their text set to the corresponding value from
In case of an earlier version of the MVC you need to do some work to get those pesky enum values and
their descriptions out. You can use
@Html.DropDownListFor helper function, although it needs
a list of
SelectListItem objects, so we need to convert the members of the enum into instances of the
that class. Here’s a way of doing this:
Both of the solutions above help you to get a user-selected value in the model on postback, but how
can you actually render that value, in its readable form, on another page? Instead of using the enum
value, we want to render the value specified in those
That’s how to get the text description out:
And put it on the model:
That’s all good, I hear you saying, but what if I have more than just one enum? Say I also want to use fields like ‘Gender’, ‘State’ and ‘Time Zone’ on my profile page. Wouldn’t it be nicer if instead of having to declare a new, slightly different function for each of those enums you could create just a generic function, that deals with any enum, as long as it adheres to the convention above?
That’s exactly the job for C# generics, which is a powerful language construct that saves you some typing. What’s more important, it makes you think harder about commonalities and differences in your code.
That’s how we can make the retrieval of
Display[Name="..."] value to work on any enum:
As you can see from above, there’s almost no difference between earlier
GetIndustryName and this
GetEnumDisplayName, except for the piece where we broaden the usage of this function to any
enum via the generic specification:
<T>(T value) where T: struct. All it really does is to say:
“accept an argument of type T as long this type is a struct” (and enums are structs in CLR).
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