Скачать или смотреть How to Properly Check INotifyDataErrorInfo for Two Related Data Fields on WPF Forms

Learn how to effectively validate two related string fields in your WPF application using `INotifyDataErrorInfo`, ensuring they are not empty and not the same.
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This video is based on the question https://stackoverflow.com/q/77640838/ asked by the user 'Thich Coi Phim' ( https://stackoverflow.com/u/944641/ ) and on the answer https://stackoverflow.com/a/77642175/ provided by the user 'EldHasp' ( https://stackoverflow.com/u/13349759/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Validating Related Data Fields in WPF

When developing a WPF application, validating user input forms is crucial, especially when interdependent fields require specific conditions to be met. A common scenario arises when you have two string fields, and you need to enforce rules that dictate these fields cannot be empty and cannot contain the same value.

For instance, consider a form where Field1 (F1) and Field2 (F2) are used. The validation rules are:

Both fields must not be empty.

Both fields must not have the same value.

After the initial validation, you may notice a discrepancy: if a user changes the value of one field, but the other field remains unchanged and is invalid, the form does not immediately reflect this state. This delay in validation raises the question: How can we ensure real-time validation without requiring the user to modify one of the fields again?

Solution Overview: Using INotifyDataErrorInfo

The solution to this problem involves leveraging the INotifyDataErrorInfo interface in WPF. This interface allows you to provide validation error information to the UI, which is essential for dynamically updating field validation states as the user interacts with the form.

Step-by-Step Implementation

1. Setting Up the ViewModel

Create a ViewModel that implements INotifyDataErrorInfo. This ViewModel will maintain the state of the fields and manage the validation logic.

Here's an outline of the ViewModel:

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

2. Implement Validation Logic

Inside the OnPropertyChanged method, you will validate the fields when either Field1 or Field2 changes:

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

3. Binding in XAML

In your XAML file, bind the text boxes to your ViewModel properties and handle the error display:

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

Conclusion

By following the steps outlined above, you can effectively implement validation for two related fields in your WPF application, ensuring that both are not empty and do not hold the same value. Utilizing INotifyDataErrorInfo paves the way for real-time validation feedback, enhancing the user experience.

This validation pattern keeps your forms clean and responsive, applying modern principles of data binding and error handling in WPF. Happy coding!