Скачать или смотреть Resolving the NullReferenceException in ASP.NET Core Razor Pages Partial Views

Learn how to fix the `NullReferenceException` in your ASP.NET Core Razor Pages when using partial views by understanding the issue and applying the right solution.
---
This video is based on the question https://stackoverflow.com/q/62377426/ asked by the user 'R_SH' ( https://stackoverflow.com/u/12131754/ ) and on the answer https://stackoverflow.com/a/62460500/ provided by the user 'R_SH' ( https://stackoverflow.com/u/12131754/ ) 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: model in partial view is null - asp.net core razor pages

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.
---
Understanding the NullReferenceException in ASP.NET Core Razor Pages

When working with ASP.NET Core Razor Pages, it’s common to utilize partial views to modularize your UI components. However, you might encounter a frustrating issue where your model in the partial view ends up being null, resulting in a NullReferenceException. Let's explore the problem and how to solve it effectively!

The Problem

In your scenario, you have a main Razor Page that references a partial view. However, the model you intend to pass to the partial view (Model.student) is coming through as null. Here’s a breakdown of the code structure you provided:

MainModel class retrieves a Student model object in its OnGet method.

The main Razor page uses the @ partial directive to load the _test2 partial view and attempts to send it the Model.student as its model.

The partial view, _test2, expects to receive a Student object but shows the error message:

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

This happens because the Model in the partial view is not set properly, leading to the exception.

The Solution

After troubleshooting, the solution is quite straightforward. The main cause of the issue is how partial views are implemented in ASP.NET Core.

Step-by-Step Fix

Remove the @ page Directive from the Partial View

The key change that resolves the issue is to eliminate the @ page directive from your partial view file. Here’s why:

The @ page directive is used in Razor pages to make them standalone pages that can handle requests directly. By having this directive in your partial view, it restricts the view from being utilized as a partial view, leading to unexpected behavior—including models being null.

Without the @ page directive, the Razor view will treat this as a partial view and it will accept models being passed to it correctly.

Here’s how your updated _test2 partial view should look:

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

Verify Your Changes

Test Your Main Page Again:
After updating the partial view, return to your main page and test the application again. You should now be able to see the Student model's Name rendered correctly without encountering a NullReferenceException.

Check Dependencies:
Ensure that your dependencies and model bindings are also correctly set up. Sometimes, other changes in code and data retrieval methods (like GetFirst()) might affect the flow, but your primary problem regarding the null reference has been addressed with the steps provided.

Conclusion

By removing the @ page directive from the partial view, you allow Razor Pages to pass the model correctly, preventing the NullReferenceException. It’s always crucial to check how you intend to use a Razor view—whether as a standalone page or as a partial view—to ensure models are correctly passed and utilized. This simple yet effective adjustment can save you a lot of time debugging and troubleshooting in your ASP.NET Core applications.

Feel free to reach out if you have further questions or run into other issues while working with ASP.NET Core Razor Pages!