HeartattacK

Asp.net MVC, Html.DropDownList and Selected Value

I recently ran into the altogether common problem of the Html.DropDownList helper rendering a drop down list with no value selected. This is a major problem when editing data as by default, the first value is selected and saving would mean the first value is used.

There have been a few issues resulting in the same error. My issue was that I was setting the Name of the drop down list to be equal to the property on my model. I was using the Entity Framework, and had an Image class with a navigation property called Category. I was using this to render the ddl:

<%= Html.DropDownList("Category", (IEnumerable<SelectListItem>)ViewData["categories"])%>

In my controller, I was setting the ViewData like this:

this.ViewData["categories"] = new SelectList(db.CategorySet.ToList(), "CategoryId", "Title", img.CategoryReference.EntityKey);

Unfortunately, even though I had set the selected value (third parameter to the SelectList constructor), the ddl had no value selected.

The fix was quite simple:

<%= Html.DropDownList("CategoryId", (IEnumerable<SelectListItem>)ViewData["categories"])%>

I just changed the Name of the drop down and handled the assignment in the controller.

The reason behind this problem is that asp.net MVC first looks for a match between the name of the drop down and a property on the model. If there’s a match, the selected value of the SelectList is overridden. Changing the name of the drop down is all it takes to remedy the issue.

 

Hope that helps.

Posted: Mar 27 2009, 11:53 AM by HeartattacK | with 16 comment(s)
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Comments

ASP.NET MVC Archived Blog Posts, Page 1 said:

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# March 28, 2009 12:36 AM

Web Development Community said:

You are voted (great) - Trackback from Web Development Community

# March 30, 2009 1:58 AM

Martin Evans said:

Thanks very much. This seems to be the only example any where on the internet where the viewdata is cast to IEnumerable<SelectListItem> in the markup!

# March 31, 2009 8:14 AM

Jeremy said:

Can you show the related code? i.e., CategorySet, CategoryReference, the controller method code?

# April 2, 2009 11:28 AM

HeartattacK said:

Sorry for the delay in getting back to this..I was setting up my new apartment, and it took a LOT of work.

The related code is very simple.

img is an Image (not System.Drawing.Image, just an Entity).

Each image has a Category. Each category can have one or mor Images.

I'm using The Entity Framework, and CategorySet is the plural of Category.

-------------------

The controller to handle the postback is like this:

public ActionResult Edit(string ImageId, string Description, int Rating, string CategoryId)

       {

           Guid imageId = new Guid(ImageId);

           var img = db.ImageSet.Where(x => x.ImageId == imageId).First();

           try

           {

               img.Description = Description;

               img.Rating = Rating;

               img.CategoryReference.EntityKey = new System.Data.EntityKey("StudiomorphEntities.CategorySet",

                  "CategoryId", new Guid(CategoryId));

.......

db.SaveChanges();

# April 27, 2009 9:03 AM

Matt said:

I was experiencing a similar problem but I was eventually able to get the selected value to show without matching the name of the dropdown to a property of the select list.

HTML -

<% =Html.DropDownList("PropertyStyleId", (SelectList)ViewData["PropertyStyles"], "(Select Style)")%>

Controller Code -

ViewData["PropertyStyles"] = new SelectList(_typeRepository.GetPropertyStyles(), "TypeId", "TypeDescription", t);

# April 28, 2009 2:43 PM

www.almny.com said:

can i get the source code for how to bind dropdownlist from mvc

# May 6, 2009 8:57 AM

Shailja Agrawal said:

This also works but the main reason of dropdownlist not showing the selected value is that the page is beingposted back whenever a button is clicked and thus the page_load event handler is called which in turn resets the selected value property , so to rectify just check in the page_load handler that wthr it is being posted back or being loaded for the first time , by inserting if page.ispostback = false.

# May 14, 2009 5:34 AM

HeartattacK said:

Shailja, this is about MVC, not webforms.

# May 14, 2009 12:59 PM

www.almny.com said:

thanks for your reply

# May 30, 2009 3:13 PM

Aaron Clausen said:

Thanks.

I discovered the same bug. Your fix worked.

Cheers

# June 15, 2009 9:56 PM

Brasileiro said:

Puta que pariu! Quero fórum em Português!! Não entendo nada que vcs falam!!!

# June 18, 2009 9:33 AM

kys said:

This issue was driving me nuts. I was tracing the SelectListItem enumeration and found that the item that I marked as selected was indeed kept selected but it was just not reflecting in the DropDownList. So, as you said, I changed the name of the DropDownList to match the property name on the model, and it worked fine. Thanks for the post. Much appreciated.

# July 20, 2009 2:17 AM

pdb said:

This really helped! Thanks!

# July 25, 2009 12:36 PM

Joel said:

Oi Brasileiro, se queresse em portugues, porque nao utilize o google translate?

# October 8, 2009 11:24 AM

Debugging, MVC TextAreas and Drop Downs Lists « Yet Another Middle Manager said:

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# December 5, 2009 11:00 AM
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