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.NET MAUI › Forms, Input & Validation

How do you implement INotifyDataErrorInfo for robust validation?

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Answer

Implement INotifyDataErrorInfo on the view model to expose per-property errors and raise ErrorsChanged. It supports async and cross-field validation and integrates with binding so the UI can reflect HasErrors and per-field messages. The MVVM Toolkit's ObservableValidator provides an attribute-driven implementation.
public partial class RegisterVm : ObservableValidator
{
    [ObservableProperty]
    [Required, EmailAddress]
    string email;

    // ValidateAllProperties() populates errors for binding
}
Real-world example A form leverages DataAnnotations via ObservableValidator so [Required]/[EmailAddress] drive both validation and error display.

Common follow-ups: What does ObservableValidator add? | Can it do cross-field rules?

Validation MVVM Toolkit Forms Input & Validation
All 6 Forms, Input & Validation questions