validate method

@override String? validate(String? value, { BuildContext? context, })

Validates the given value. Returns an error message String if validation fails, otherwise returns `null].

The context can optionally be used by rules needing access to localization, etc. This context is provided by the FieldValidator when getValidator is called.

Implementation

@override
String? validate(String? value, {BuildContext? context}) {
  if ((value ?? '').trim().isEmpty)
    return null; // Don't validate empty strings
  return double.tryParse(value!) == null ? message : null;
}