Binding Data to Forms

binder.forField(emailField)
  // Explicit validator instance
  .withValidator(new EmailValidator(
    "This doesn't look like a valid email address"))
  .bind(Person::getEmail, Person::setEmail);

binder.forField(nameField)
  // Validator defined based on a lambda and an error message
  .withValidator(
    name -> name.length() >= 3,
    "Full name must contain at least three characters")
  .bind(Person::getName, Person::setName);

binder.forField(titleField)
  // Shorthand for requiring the field to be non-empty
  // This is conditional on Binding::setAsRequiredEnabled(boolean)
  .asRequired("Every employee must have a title")
  .bind(Person::getTitle, Person::setTitle);

Label emailStatus = new Label();

binder.forField(emailField)
  .withValidator(new EmailValidator(
    "This doesn't look like a valid email address"))
  // Shorthand that updates the label based on the status
  .withStatusLabel(emailStatus)
  .bind(Person::getEmail, Person::setEmail);

Label nameStatus = new Label();

binder.forField(nameField)
  // Define the validator
  .withValidator(
    name -> name.length() >= 3,
    "Full name must contain at least three characters")
  // Define how the validation status is displayed
  .withValidationStatusHandler(status -> {
      nameStatus.setValue(status.getMessage().orElse(""));
      nameStatus.setVisible(status.isError());
    })
  // Finalize the binding
  .bind(Person::getName, Person::setName);

binder.forField(emailField)
  .withValidator(new EmailValidator(
    "This doesn't look like a valid email address"))
  .withValidator(
    email -> email.endsWith("@acme.com"),
    "Only acme.com email addresses are allowed")
  .bind(Person::getEmail, Person::setEmail);

Binder<Trip> binder = new Binder<>();
DateField departing = new DateField("Departing");
DateField returning = new DateField("Returning");

// Store return date binding so we can revalidate it later
Binder.BindingBuilder<Trip, LocalDate> returnBindingBuilder = binder.forField(returning)
  .withValidator(returnDate -> !returnDate.isBefore(departing.getValue()),
  "Cannot return before departing");
Binder.Binding<Trip, LocalDate> returnBinder = returnBindingBuilder.bind(Trip::getReturnDate, Trip::setReturnDate);

// Revalidate return date when departure date changes
departing.addValueChangeListener(event -> returnBinder.validate());

TextField yearOfBirthField = new TextField("Year of birth");

binder.forField(yearOfBirthField)
  .withConverter(
    new StringToIntegerConverter("Must enter a number"))
  .bind(Person::getYearOfBirth, Person::setYearOfBirth);

// Slider for integers between 1 and 10
Slider salaryLevelField = new Slider("Salary level", 1, 10);

binder.forField(salaryLevelField)
  .withConverter(Double::intValue, Integer::doubleValue)
  .bind(Person::getSalaryLevel, Person::setSalaryLevel);

binder.forField(yearOfBirthField)
  // Validator will be run with the String value of the field
  .withValidator(text -> text.length() == 4,
    "Doesn't look like a year")
  // Converter will only be run for strings with 4 characters
  .withConverter(
    new StringToIntegerConverter("Must enter a number"))
  // Validator will be run with the converted value
  .withValidator(year -> year >= 1900 && year < 2000,
    "Person must be born in the 20th century")
  .bind(Person::getYearOfBirth, Person::setYearOfBirth);

binder.forField(yearOfBirthField)
  .withConverter(
    Integer::valueOf,
    String::valueOf,
    // Text to use instead of the NumberFormatException message
    "Please enter a number")
  .bind(Person::getYearOfBirth, Person::setYearOfBirth);

class MyConverter implements Converter<String, Integer> {
  @Override
  public Result<Integer> convertToModel(String fieldValue, ValueContext context) {
    // Produces a converted value or an error
    try {
      // ok is a static helper method that creates a Result
      return Result.ok(Integer.valueOf(fieldValue));
    } catch (NumberFormatException e) {
      // error is a static helper method that creates a Result
      return Result.error("Please enter a number");
    }
  }

  @Override
  public String convertToPresentation(Integer integer, ValueContext context) {
    // Converting to the field type should always succeed,
    // so there is no support for returning an error Result.
    return String.valueOf(integer);
  }
}

// Using the converter
binder.forField(yearOfBirthField)
  .withConverter(new MyConverter())
  .bind(Person::getYearOfBirth, Person::setYearOfBirth);

Person person = new Person("John Doe", 1957);

binder.readBean(person);

// This will make all current validation errors visible
BinderValidationStatus<Person> status = binder.validate();

if (status.hasErrors()) {
  Notification.show("Validation error count: "
    + status.getValidationErrors().size());
}

binder.addStatusChangeListener(event -> {
  boolean isValid = event.getBinder().isValid();
  boolean hasChanges = event.getBinder().hasChanges();

  saveButton.setEnabled(hasChanges && isValid);
  resetButton.setEnabled(hasChanges);
});

Binder<Person> binder = new Binder<>();

// Field binding configuration omitted, it should be done here

Person person = new Person("John Doe", 1957);

// Loads the values from the person instance
// Sets person to be updated when any bound field is updated
binder.setBean(person);

Button saveButton = new Button("Save", event -> {
  if (binder.validate().isOk()) {
    // person is always up-to-date as long as there are no
    // validation errors

    MyBackend.updatePersonInDatabase(person);
  }
});