Скачать или смотреть Resolving the Dropdownlist as selected in ASP.NET MVC using ViewBag Error

Discover how to effectively troubleshoot the error related to Dropdownlists in ASP.NET MVC using ViewBag, ensuring a seamless user experience in your web applications.
---
This video is based on the question https://stackoverflow.com/q/63012607/ asked by the user 'Said' ( https://stackoverflow.com/u/13791921/ ) and on the answer https://stackoverflow.com/a/63012876/ provided by the user 'Süleyman Sümertaş' ( https://stackoverflow.com/u/5331231/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Dropdownlist as selected in ASP.NET MVC using ViewBag?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Troubleshooting Dropdownlist Issues in ASP.NET MVC using ViewBag

When developing web applications with ASP.NET MVC, you might encounter a frustrating problem with dropdown lists, particularly when trying to display them in a Bootstrap modal. One common error that developers face is: "Server Error in '/' Application. There is no ViewData item of type 'IEnumerable' that has the key 'DepartmentId'". This can lead to a lot of confusion, especially when you expect everything to be working smoothly. In this guide, we’ll dive into the issue and provide a step-by-step guide to resolve it.

Understanding the Problem

The issue arises when you're trying to bind a dropdown list within a Bootstrap modal. This dropdown is expected to be populated with department data from the database. The primary cause of the error is that when the partial view is rendered, it does not have access to the ViewBag items that were populated in the main view's action method. Essentially, ViewBag scope is limited to the individual request that produced it, meaning you cannot access data set in one request from a subsequent request.

The Error Message

Error: "There is no ViewData item of type 'IEnumerable' that has the key 'DepartmentId'."

Location: This error typically occurs when you attempt to call a dropdown list in a partial view without ensuring the necessary data is available in that context.

Step-by-Step Solution

To solve the problem effectively, follow these organized steps:

Step 1: Update the Partial View

In your partial view where you're trying to render the dropdown list, ensure you're properly fetching and assigning the relevant data as follows:

Instead of this line:

[[See Video to Reveal this Text or Code Snippet]]

Change it to:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Populate the ViewBag in the Relevant Action Method

Since the dropdown list is being accessed in the partial view, you need to populate the ViewBag with the required department data in the correct action method. Update your GetStudentPartial method like this:

[[See Video to Reveal this Text or Code Snippet]]

This change ensures that when the partial view is requested, it has the necessary department data.

Conclusion

Troubleshooting issues with dropdowns in ASP.NET MVC can be challenging, especially when working with ViewBag and partial views. By following the steps outlined above, you can effectively resolve the error and ensure that your dropdown list displays correctly. Remember to always check if the necessary data is accessible from within the scope of the action method you’re currently working in.

Implement these changes to avoid runtime errors and enhance the user experience of your web application. Happy coding!