required static method

FormFieldValidator<String> required(String errorMessage)

Validator that requires the field have a non-empty value.

Validate that the field is non-empty

         TextFormField(
             labelText: 'Required',
           ),
           validator: Validators.required('Field is required'),
         ),

Implementation

static FormFieldValidator<String> required(String errorMessage) {
  return (value) {
    if (value == null) {
      value = '';
    }
    if (value.isEmpty)
      return errorMessage;
    else
      return null;
  };
}