Скачать или смотреть Resolving the XFC0009 Error: Binding Custom Behaviors in Xamarin.Forms with Prism

Learn how to fix the `XFC0009` error when binding properties in custom behaviors for Xamarin.Forms. This guide walks you through common pitfalls and solutions.
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Resolving the XFC0009 Error: Binding Custom Behaviors in Xamarin.Forms with Prism

When working with Xamarin.Forms, especially with custom behaviors, developers often encounter various binding issues. One particularly confusing error is XFC0009: No property, BindableProperty, or event found for "CodeInString", or mismatching type between value and property. In this post, we’ll delve into what causes this error when utilizing custom behaviors and how to resolve it effectively.

Understanding the Problem

You may face this error when trying to bind a property from your ViewModel to a custom behavior defined for an Entry control, particularly when the behavior involves a BindableProperty.

In your case, you have created a custom behavior called MobileNumberValidation with several properties including MobileCountryCode. Initially, the binding works fine when using hardcoded string values. However, when you attempt to bind a property (like CodeInString) from your ViewModel, the error arises.

Common Symptoms

Successful binding with hardcoded values.

Error messages when trying to bind to ViewModel properties.

The error typically indicates that the specified property cannot be found in the expected context.

Solution Steps

To address the XFC0009 error when binding properties within your custom behavior:

1. Review Your OnAttachedTo Method

In your MobileNumberValidation class, the OnAttachedTo method assigns the binding context based on the Entry that the behavior is attached to:

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

Issue: The problem is that this assignment occurs before the main page has set its BindingContext, causing this.BindingContext to be null.

Action: To fix this, you should not set the BindingContext here.

2. Set the BindingContext in XAML

Instead of adjusting the BindingContext within the behavior, set it directly in your XAML where you use the MobileNumberValidation behavior. Here, you can set the BindingContext of the behavior to that of the Entry itself:

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

3. Clean Up Your Code

Ensure that any code relating to binding context manipulation within the OnAttachedTo method is removed as it's no longer necessary. This will help avoid confusion and unnecessary errors.

4. Test the Binding

After implementing these changes, test your application to verify if the binding to CodeInString and any other properties are functional without errors.

Conclusion

Binding issues like the XFC0009 error can cause significant roadblocks during development in Xamarin.Forms. By properly managing the BindingContext in your custom behavior, you can avoid common pitfalls and streamline your development process. If you continue to have issues, retrace your steps and ensure all bindings and contexts are set up correctly.

Remember, without the appropriate context, properties may become inaccessible, leading to frustrating errors. Happy coding!