Solving Null Reference Exceptions in Razor Pages When The OnGetAsync Method Isn't Hit

Discover how to resolve `Null Reference Exceptions` occurring in Razor Pages when the `OnGetAsync` method fails to execute properly.
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Fixing Null Reference Exceptions in Razor Pages

In ASP.NET Core Razor Pages, encountering a Null Reference Exception can be frustrating, especially if breakpoints in your code seem to be completely ignored. This post addresses a common issue where the OnGetAsync method is either not executing or failing to complete before the page renders, resulting in null data in your model. Let’s explore this problem step-by-step and view a clear solution.

The Problem: Null Reference Exception in Razor View

While working with .NET Core 7 Razor Pages, you may find that when your webpage loads, it throws a null reference exception for the Model.Sections property. Despite setting breakpoints in your OnGetAsync method, it's as if the method is never being hit, leading to confusion and frustration. Let's look at your HTML and C- code structure to understand why this might be happening.

C- Code Structure

Here is the relevant part of your C- Razor Pages code:

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

This method is intended to fetch a list of sections from the database and populate the ManageSectionVM.Sections property. However, if this method isn't executed, you'll face this null reference exception when trying to access Model.Sections in your Razor view.

HTML Code Structure

Here’s the related Razor view code where the exception occurs:

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

The Solution: Correcting Model References in Razor Pages

To solve the issue, we need to ensure the Razor view model matches the C- Page Model class. Follow these steps to fix the problem:

Step 1: Update the Model in the Razor View

Change the declaration of the model in your Razor view from -model ManageSectionVM to -model ManageSectionModel. This aligns the view with the PageModel that you are using.

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

Step 2: Update bound properties in the HTML

Next, adjust the ASP.NET Razor tags to reflect the updated model reference. Change the model-specific properties in your HTML to match the new structure. This includes:

Updating asp-for attributes

Updating asp-items references

Here is how the revised HTML should look:

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

Recap: Important Changes

Changed the model in the Razor view to -model ManageSectionModel.

Modified asp-for from SelectedSectionID to ManageSectionVM.SelectedSectionID.

Updated asp-items to point to Model.ManageSectionVM.Sections.

Final Thoughts

By applying these adjustments, you ensure that the Razor view correctly references the properties of your Page Model. This should resolve the Null Reference Exception problem and allow the OnGetAsync method to execute as intended, populating your model before the page renders. Happy coding!