


Why Does My Dropdown List Throw a 'System.Int32' vs. 'IEnumerable' Error?
Feb 03, 2025 am 03:06 AMTroubleshooting "System.Int32" vs. "IEnumerable" Errors in Dropdown Lists
Submitting a form with a dropdown list can sometimes result in an error indicating a type mismatch: the ViewData
item expects an IEnumerable
type (for the dropdown options), but receives a System.Int32
instead.
Root Cause: Null Category List
This typically happens because the CategoryList
property within your view model (e.g., ProjectVM
) is null
when the form is submitted. The ViewData
relies on this property to populate the dropdown list.
Solution: Repopulate the Category List in the POST Method
The solution is to explicitly repopulate the CategoryList
property within your controller's POST action method before returning the view. This ensures the correct IEnumerable
data is available in the ViewData
.
Here's how to modify your POST method:
public ActionResult Create(ProjectVM model) { if (!ModelState.IsValid) { // Repopulate the CategoryList model.CategoryList = new SelectList(db.Categories, "ID", "Name"); return View(model); } // ... (Your existing code to save the model and redirect) ... }
Adding this line re-creates the SelectList
and assigns it to model.CategoryList
. This, in turn, provides the necessary IEnumerable
data to the DropDownListFor()
helper in your view.
How it Works: ViewData and SelectList
The DropDownListFor()
helper method (and DropDownList()
) tries to find the appropriate SelectList
data. If it doesn't receive a SelectList
directly, it looks for data in ViewData
using the property name (like 'CategoryID'). If the ViewData
item isn't castable to IEnumerable
, the type mismatch error occurs. By explicitly setting CategoryList
in the POST method, we bypass this issue.
The above is the detailed content of Why Does My Dropdown List Throw a 'System.Int32' vs. 'IEnumerable' Error?. For more information, please follow other related articles on the PHP Chinese website!

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