Troubleshooting and Debugging Tips

Congratulations on making it this far in your journey to mastering the MVVM pattern in .NET MAUI! By now, you’ve learned about the intricacies of data binding, dependency injection, converters, and various other components that make up your Recipes! app. However, as any seasoned developer will tell you, even the most experienced experts encounter roadblocks from time to time.

MVVM, with all its benefits, can sometimes feel like navigating a complex maze. When you encounter issues, it’s not always obvious where to find the root cause or how to fix it. That’s where this chapter comes in. In this short but invaluable chapter, we’ll shine a light on common pitfalls and challenges you may face during your MVVM journey.

We’ll explore three areas where issues often tend to occur:

• Common data binding issues
• Services and Dependency Injection pitfalls
• Frequent custom control and converter problems
...

Technical requirements

To ensure you’re in sync with the upcoming content, make your way to our GitHub repository at https://github.com/PacktPublishing/MVVM-pattern-.NET-MAUI/tree/main/Chapter14. Kick off with the materials in the Start folder. And remember, if you’re ever in need of a consolidated reference, the Finish folder holds the final, refined code at the chapter’s close.

Common data binding issues

One of the cornerstones of the MVVM pattern is data binding. It forms the link between your View and ViewModel, ensuring seamless communication between them. While data binding offers powerful capabilities, it’s also an area where developers often face challenges. This section aims to shed light on common data binding and ViewModel issues and how to troubleshoot them:

• Typos and mismatched names: One of the simplest yet surprisingly common issues developers encounter is typos or mismatched property names. A small typo in your XAML markup or ViewModel code can disrupt the entire data binding process.
• Incorrect binding modes: Data binding supports various modes such as OneWay, TwoWay, and OneTime, each with its own purpose, as we’ve seen in Chapter 4, Data Binding in .NET MAUI. Using the wrong mode can lead to unexpected behavior in your app.
• Binding incompatible data types: Obviously, binding a property of type int to a property...

Services and Dependency Injection pitfalls

In your MVVM journey, DI plays a crucial role in providing essential functionality to your application. However, even in the world of DI, there can be pitfalls waiting to catch you off guard. This section is dedicated to unveiling the most common pitfalls and equipping you with the knowledge to navigate them effectively.

Unable to resolve service for type

A System.InvalidOperationException stating Unable to resolve service for type … is one of the most frequent exceptions when working with DI. The cause is pretty simple: we ask the DI container to resolve an instance of an object that has some dependencies that can’t be resolved. In other words, we haven’t registered all dependencies for this class. Figure 14.2 shows what this exception would look like if we didn’t register the RecipesOverviewViewModel in the DI container:

Figure 14.2: InvalidOperationException thrown

The exception...

Frequent custom control and converter problems

Most of the issues that arise when working with custom controls regularly have to do with bindable properties. Often, a small typo or a little oversight might cause your custom control to not react as expected or to display the wrong data.

Troubleshooting bindable properties

On a custom control, there is a lot of ceremony needed to define bindable properties. It’s very easy to make a mistake that is very hard to spot when troubleshooting. Here are a couple of things to look out for:

• The propertyName parameter in the Create method: Make sure the propertyName parameter matches the exact naming of the property:

  public static readonly BindableProperty
    IsFavoriteProperty =
      BindableProperty.Create(nameof(IsFavorite), …);
  public bool IsFavorite
  {
      ...
  }

  As this code sample shows, it is advised to use the nameof expression to prevent typos!

• The returnType parameter...

Summary

Now that we’ve reached the end of this short chapter, I hope you’ve gained valuable insights and tips for effectively troubleshooting issues that can arise in an MVVM context. Remember, the road to mastering MVVM is an ongoing journey, and troubleshooting and debugging are indispensable companions on this path. These challenges, though sometimes frustrating, are valuable teachers that will deepen your understanding and proficiency in MVVM. Embrace them as opportunities to grow, and in doing so, you’ll become a more proficient and confident MVVM developer. Your journey doesn’t end here; it evolves with each issue you resolve.

As we wrap up this final chapter, I want to extend my heartfelt congratulations to you for completing this book’s journey into the world of MVVM in .NET MAUI. Throughout this book, you’ve delved into the intricacies of the MVVM pattern, explored the capabilities of .NET MAUI, and built your very own Recipes!...

Further reading

To learn more about the topics that were covered in this chapter, take a look at the following resource:

XAML data binding diagnostics: https://learn.microsoft.com/en-us/visualstudio/xaml-tools/xaml-data-binding-diagnostics?view=vs-2022