appendix-vaadin-components.asciidoc

title	order	layout
Appendix: Binding Data to Vaadin Components	100	page

Binding Data to Vaadin Components

Client Form binder supports out-of-the-box the set of form elements present in Vaadin Components. It means that data binding, type mapping, required flag, and validation messages will work without any extra work.

Configuring Server Data and Endpoint

When defining Bean objects in Java, apart from the type we can define validation and error messages.

For this article, the code in the client-side will be based on the data and endpoints defined in the following java classes:

public class MyEntity {
    @AssertTrue(message = "Please agree this")
    Boolean myBooleanField = false;

    @NotEmpty(message = "Select at least one option")
    List<String> myListField = Arrays.asList("item-1");

    @Pattern(regexp = "(?=.*\\d)(?=.*[a-z])(?=.*[A-Z]).{8,}",
                message = "must be 8+ characters, with uppercase, lowercase, and numbers")
    String myPasswordField = "bar";

    @Email(message = "must be a valid email address")
    String myEmailField = "foo@bar.baz";

    @PositiveOrZero(message = "Should be positive or zero")
    Integer myIntegerField = 12;
    @Positive(message = "Should be positive")
    Double myDoubleField = 12.33d;

    @Future(message = "Should be a date in the future")
    LocalDate myDateField = LocalDate.now().plusDays(1);
    LocalDateTime myDateTimeField = LocalDateTime.now();
    LocalTime myTimeField = LocalTime.now();

    @Min(0) @Max(1)
    Integer mySelectField = 1;
}

@Endpoint
public class MyEndpoint {
    public MyEntity getMyEntity() {
        return new MyEntity();
    }

    public List<String> getMyOptions() {
        return Arrays.asList("item-1", "item-2", "item-3");
    }
}

Configuring client fields

Before using form binders, you need to import your entity models and instantiate the binder, as well as perform the endpoint call for getting the entity value, as it is explained in tutorials Binding Data to Client-Side Forms and Loading from and Saving to Business Objects respectively.

For this article, these are the significant lines needed in the view:

import * as endpoint from '../../generated/MyEndpoint';
import MyEntityModel from '../../generated/com/example/MyEntityModel';
...
const binder = new Binder(this, MyEntityModel);
...
async firstUpdated(arg: any) {
  super.firstUpdated(arg);
  this.binder.read(await endpoint.getMyEntity());
}

Binding data to Text and Number fields

No extra action is needed for configuring the Vaadin components present in the vaadin-text-field package.

import '@vaadin/vaadin-text-field';
...
render() {
  return html`
  <vaadin-text-field ...="${field(this.binder.model.myTextField)}" label="string"></vaadin-text-field>
  <vaadin-password-field ...="${field(this.binder.model.myPasswordField)}" label="password"></vaadin-password-field>
  <vaadin-integer-field ...="${field(this.binder.model.myIntegerField)}" label="integer" has-controls></vaadin-integer-field>
  <vaadin-number-field ...="${field(this.binder.model.myDoubleField)}" label="number" has-controls></vaadin-number-field>
  <vaadin-email-field ...="${field(this.binder.model.myEmailField)}" label="email"></vaadin-email-field>
  <vaadin-text-area ...="${field(this.binder.model.myTextField)}" label="textarea"></vaadin-text-area>
  `;
}

Binding data to Boolean fields

There are two elements in Vaadin to deal with booleans: vaadin-checkbox and vaadin-radio-button, both work fine with form binders, but neither of them have validation and failure styling, thus you need some extra work for giving error feedback. In the following snippet the background color is changed on validation error.

import '@vaadin/vaadin-checkbox';
import '@vaadin/vaadin-radio-button';
...
static get styles() {
  return css`
    vaadin-checkbox[invalid], vaadin-radio-button[invalid],
      background: var(--lumo-error-color-10pct);
    }`;
}
...
render() {
  return html`
  <vaadin-checkbox ...="${field(this.binder.model.myBooleanField)}">checkbox</vaadin-checkbox>
  <vaadin-radio-button ...="${field(this.binder.model.myBooleanField)}">radio-button</vaadin-radio-button>
  `;
}

Binding data to list fields

Vaadin has several components for selection based on option lists, each one covering a specific purpose, hence the way to set their values and options differs.

Configuring the options for selection

Options for these components can be set by calling a server side service that provides the list of strings. Since the call to the endpoint is asynchronous, one easy way is to combine the until and repeat methods in the lit-html library.

As reference, the following snippet demonstrates how to repeat a pattern given an asynchronous method that returns a list of items. The same pattern will be used in the code blocks for each component below.

import {until} from 'lit-html/directives/until.js';
import {repeat} from 'lit-html/directives/repeat.js';
...
render() {
  return html`
  ...
    ${until(endpoint.getMyOptions().then(opts => repeat(opts, (item) => html`
      <div>${item}</div>
    `)))}
  ...
  `;
}

Single selection using the item value

For a single selection vaadin-combo-box, vaadin-radio-group or vaadin-list-box should be used. All of them can take the selected item value as a string.

import '@vaadin/vaadin-combo-box';
import '@vaadin/vaadin-list-box';
import '@vaadin/vaadin-radio-button/vaadin-radio-group';
...
render() {
  return html`
  <vaadin-combo-box ...="${field(this.binder.model.mySingleSelectionField)}"
    .items="${until(endpoint.getMyOptions())}" label="combo-box">
  </vaadin-combo-box>

  <vaadin-radio-group ...="${field(this.binder.model.mySingleSelectionField)}" label="radio-group">
    ${until(endpoint.getMyOptions().then(opts => repeat(opts, (item) => html`
      <vaadin-radio-button value="${item}">${item}</vaadin-radio-button>
    `)))}
  </vaadin-radio-group>

  <vaadin-list-box ...="${field(this.binder.model.mySingleSelectionField)}" label="list-box">
    ${until(endpoint.getMyOptions().then(opts => repeat(opts, (item) => html`
      <vaadin-item><span>${item}</span></vaadin-item>
    `)))}
  </vaadin-list-box>
  `;
}

Single selection using index

To select items by index, the vaadin-select component should be used. It accepts an integer for the index value. Because this component is configurable via the template tag, it’s not possible to set the options with an asynchronous call.

import '@vaadin/vaadin-select';
...
render() {
  return html`
  <vaadin-select ...="${field(this.binder.model.mySelectField)}" label="select">
    <template>
      <vaadin-list-box>
        <vaadin-item><span>item-1</span></vaadin-item>
        <vaadin-item><span>item-2</span></vaadin-item>
      </vaadin-list-box>
    </template>
  </vaadin-select>
  `;
}

Multiple selection

The Vaadin component for multiple selection is the vaadin-checkbox-group which accepts an array of strings.

import '@vaadin/vaadin-checkbox/vaadin-checkbox-group';
...
render() {
  return html`
  <vaadin-checkbox-group ...="${field(this.binder.model.myListField)}" label="check-group">
    ${until(endpoint.getMyOptions().then(opts => repeat(opts, (item) => html`
      <vaadin-checkbox value="${item}">${item}</vaadin-checkbox>
    `)))}
  </vaadin-checkbox-group>
  `;
}

Binding data to Date and Time fields

Use vaadin-date-picker for binding to Java LocalDate, vaadin-time-picker for LocalTime, and vaadin-date-time-picker for LocalDateTime.

import '@vaadin/vaadin-date-picker';
import '@vaadin/vaadin-time-picker';
import '@vaadin/vaadin-date-time-picker';
...
render() {
  return html`
  <vaadin-date-picker ...="${field(this.binder.model.myDateField)}" label="date"></vaadin-date-picker>
  <vaadin-time-picker ...="${field(this.binder.model.myTimeField)}" label="time"></vaadin-time-picker>
  <vaadin-date-time-picker ...="${field(this.binder.model.myDateTimeField)}" label="date-time"></vaadin-date-time-picker>
  `;
}

Wrapping components in custom fields

Vaadin provides the vaadin-custom-field that can be used to wrap one or multiple vaadin fields. It works with the following components:

• vaadin-text-field

• vaadin-number-field

• vaadin-password-field

• vaadin-text-area

• vaadin-select

• vaadin-combo-box

• vaadin-date-picker

• vaadin-time-picker

import '@vaadin/vaadin-custom-field';
import '@vaadin/vaadin-text-field';
...
render() {
  return html`
  <vaadin-custom-field ...="${field(this.binder.model.myTextField)}" label="custom-field">
    <vaadin-text-field></vaadin-text-field>
  </vaadin-custom-field>
  `;
}

Note	There are limitations on using vaadin-custom-field with other elements listed above:

• value to the custom field should be provided as a string

• children should have the value property in their API.