ReactiveUI.Validation Issues with TextBox: The Infinite Loop Problem

Описание: Discover how to solve the common issue of `ReactiveUI.Validation` not working with `TextBox` in WPF when using `UpdateSourceTrigger` set to `PropertyChanged`.
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This video is based on the question https://stackoverflow.com/q/67225774/ asked by the user 'Prodromos' ( https://stackoverflow.com/u/6544768/ ) and on the answer https://stackoverflow.com/a/67229144/ provided by the user 'Lukasz Szczygielek' ( https://stackoverflow.com/u/8212196/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: ReactiveUI.Validation Not Working

If you're diving into the world of ReactiveUI and WPF, you might encounter a peculiar problem: ReactiveUI.Validation may not function correctly on a TextBox when you use UpdateSourceTrigger=PropertyChanged. This problem can be daunting, especially when you're eager to learn and implement reactive programming. In this post, we'll explore what's causing this issue and provide a clear solution to get your validation working smoothly.

The Problem

In your case, you have set up a simple TextBox but faced an issue where typing in the field caused the application to hang. On observing the behavior:

When you bind the TextBox using UpdateSourceTrigger=PropertyChanged, it creates an infinite loop.

This happens because the binding reads input from the TextBox, updates the associated property, and then triggers the ValidationRule to update the control.

Analyzing the Code

Let's break it down with regard to the code you provided:

MainWindow XAML

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

Code Behind

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

ViewModel

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

As you can see, there are several interconnected components at play in the code. The main culprit leading to the infinite loop arises from the BindValidation call.

Solution: Breaking the Infinite Loop

To resolve this issue effectively, you need to recognize the proper usage of the BindValidation method. Here are the steps to fix the problem:

Steps to Follow

Remove the BindValidation Call:

The BindValidation is incorrectly set up in your code. Since you're already using XAML bindings for your TextBox, it handles error messages related to validation properly.

Correct Binding Approach:

Stick to the built-in WPF mechanism that leverages INotifyDataErrorInfo.

Update your XAML to remove manual error handling.

The updated version of your WhenActivated method should look like this:

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

Conclusion

By understanding the relationship between your UI components and validation logic in ReactiveUI, you can prevent infinite loops and ensure that your validation works as expected. The key takeaway here is to utilize WPF's built-in mechanisms for validation and properly structure your bindings.

Now, with this corrected approach, you should find that your TextBox performs seamlessly while also providing effective validation feedback as you type. Happy coding with ReactiveUI!