Resolving the NullReferenceException in ASP.NET Core When Using Page Models

Discover how to fix the issue with your Page Model not being constructed in ASP.NET Core, leading to `NullReferenceException` errors when rendering your views.
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Resolving the NullReferenceException in ASP.NET Core When Using Page Models

In the world of ASP.NET Core application development, encountering unexpected errors can be frustrating. One such issue that developers often run into is when the Page Model for a Razor page does not get constructed correctly, leading to a NullReferenceException. This guide will explore the causes of this problem and provide a practical solution to ensure your Page Model is instantiated correctly, allowing your application to function seamlessly.

The Problem

You might be facing a scenario where your ASP.NET Core application experiences a NullReferenceException when trying to render your Razor page. Here’s a brief overview of the symptoms you might be observing:

The constructor of your IndexModel Page Model is never called.

The application throws a NullReferenceException indicating that an object reference is not set to an instance of an object, especially when trying to access properties of your model.

Example Error Output

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

Current Setup

Your current setup involves the following:

A HomeController that routes to the Index view

The fundamental issue is that the Page Model isn't being constructed when your view is called.

The Solution

To resolve this issue, you need to ensure that the Page Model is correctly initialized when the view is requested. Here's how you can do it:

Step 1: Modify the HomeController

Instead of returning the view without any model, modify your HomeController to pass an instance of the IndexModel to the view directly as shown below:

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

Step 2: Understand the Change

Final Thoughts

When working with ASP.NET Core and Razor Pages, it’s crucial to understand the flow of data between your controllers and views. The modification we introduced helps clarify the relationship and ensures your Page Model is constructed properly before rendering.

With this addition, your Razor page should now render without throwing any exceptions, and you will see your history items displayed correctly. If you run into further issues, always check to make sure that your models are being instantiated properly and that any required properties are set before attempting to access them in your views.

By implementing this simple change, you can avoid the frustration of encountering a NullReferenceException and keep your application running smoothly.