Solving the NullReferenceException in WPF with Nested Generics

Learn how to overcome `NullReferenceExpections` caused by nested generics in WPF applications by implementing a structured base class approach.
---

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: Custom Window with nested Generics produces NullReferencEException without Inner Exception

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the NullReferenceException in WPF Applications

When developing WPF applications using C# and .NET Core, you might encounter frustrating runtime issues, especially when dealing with generics and data bindings. One particularly common and puzzling error is the NullReferenceException, which can occur seemingly without reason.

In this guide, we will focus on a specific scenario involving custom window and controller relationships that lead to this exception. After explaining the problem, we’ll walk through an efficient solution that can make your code cleaner and more robust.

The Problem: Nested Generics Causing Runtime Issues

You've created a sophisticated structure using nested generics in your WPF application. As shown in the example code provided, the relationship is established between a Window and a Controller, both of which rely on generics to streamline your window management. The intent was to eliminate boilerplate code that duplicates across different windows.

However, without any bindings set up initially, hitting the constructor of your MainWindow leads to a NullReferenceException that lacks any informative message or inner exception. This renders the debugging process challenging and adds frustration to the development experience.

Example Code:

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

What could possibly go wrong? The issue appears to stem from how WPF interacts with your generics, particularly within the context of the XAML file, which causes the underlying exceptions.

The Solution: Custom Base Abstract Class

To tackle this, you can implement an intermediary base class that decouples the generics from the WPF framework. This approach involves creating a single one-liner abstract class that wraps the generics. This will allow for more straightforward handling and can effectively resolve the NullReferenceException.

Step-by-step Implementation

Define an abstract class that explicitly types the generics while still providing your original functionality.

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

Modify your controller to use the newly created base class, ensuring it maintains the necessary commands.

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

Define a new base class that inherits from ControlledWindowBase without generics, making the constructor straightforward.

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

Adjust the MainWindow XAML:
Your XAML no longer needs the x:TypeArguments since inheritance is resolved via the new base class.

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

Benefits of This Approach

Simplicity: Reduces the complexity of your types by removing the generics from the UI layer.

Robustness: Prevents NullReferenceExceptions by ensuring that the types are properly inferred and enforced.

Maintains Functionality: Keeps your original coding structure but makes it more WPF-friendly.

Conclusion

By understanding the nuances of how generics can interact with WPF components, you are better equipped to avoid runtime exceptions that arise in these scenarios. Utilizing an intermediary base class can resolve these issues and streamline your implementation.

If you’re facing similar problems in your WPF applications, consider adopting the structure we've outlined here for a more predictable and error-free development experience. Happy coding!