midFlutter
How do you handle form validation?
Updated Apr 28, 2026
Short answer
By using the Form widget with a GlobalKey<FormState> and TextFormField validation logic.
Deep explanation
You wrap your input fields in a Form widget and assign a GlobalKey<FormState>. Each TextFormField receives a validator function returning a string (error) or null (success). Calling formKey.currentState!.validate() triggers all validators.
Real-world example
Creating a user registration screen ensuring emails have the correct format and passwords are at least 8 characters.
Common mistakes
- Forgetting to wrap TextFields in a Form widget and trying to manage validation state manually via `setState`.
Follow-up questions
- How do you save form data?
- What is autoValidateMode?