How do you build and validate forms in Flutter?

A Form groups fields and exposes validate and save through a GlobalKey. Each TextFormField validator returns an error string or null. Validation is synchronous and local; asynchronous or server-side rules need explicit loading and error handling.

final formKey = GlobalKey<FormState>();
final emailController = TextEditingController();

Widget buildEmailField() {
  return Form(
    key: formKey,
    child: TextFormField(
      controller: emailController,
      keyboardType: TextInputType.emailAddress,
      autofillHints: const [AutofillHints.email],
      validator: (value) {
        final text = value?.trim() ?? '';
        if (!text.contains('@')) return 'Enter a valid email';
        return null;
      },
    ),
  );
}

bool submit() {
  return formKey.currentState?.validate() ?? false;
}

• Dispose every TextEditingController and FocusNode in State.dispose
• Use autovalidateMode deliberately; validating on every keystroke can feel hostile
• Use inputFormatters for formatting and maxLength for hard limits
• Set textInputAction and focus traversal so keyboard navigation is sensible
• Expose errors through Semantics and keep labels visible for screen readers

Server errors and submission

Disable the submit button while a request is in flight and guard against double taps. Map field-level server errors back to the relevant controller or validator. Keep a form-level error area for problems that are not tied to one field. On success, clear sensitive controllers before leaving the screen.