Binding to Template Components

How to use the @Id annotation to reference a JavaScript LitElement template.

The @Id annotation allows you to interact with client-side templates on the server side. You can use the @Id annotation to get a Component or Element reference for an element defined in a JavaScript template.

This section demonstrates how to use the @Id annotation to reference a JavaScript LitElement template. The same logic applies to Polymer templates.

Example: MainPage TypeScript LitElement template file.

Source code

JavaScriptclass MainPage extends LitElement {
  render() {
    return html`
      <div id="content"></div>
      <button id="helloButton">Click me!</button>
    `;
  }
}

customElements.define('main-page', MainPage);

The html returns a placeholder div element with a "content" identifier and button element with a helloButton identifier.
The div element is mapped to a Div component in the Java code (see below), allowing you to add a Component as a child to it.
The button element is mapped to a NativeButton component in the Java code (see below), allowing you to react to its click events.

Example: Implementing a method in the MainPage class to add a Component to the content of a TypeScript LitElement template element.

Note	The return statement in the render method needs to end with a semi-colon (`;`) for the parser to find the template contents.

Source code

Java@Tag("main-page")
@JsModule("./com/example/main-page.ts")
public class MainPage extends LitTemplate {

    @Id("content")
    private Div content;

    @Id("helloButton")
    private NativeButton helloButton;

    public MainPage() {
        helloButton.addClickListener(event -> {
           System.out.println("Clicked!");
        });
    }

    public void setContent(Component content) {
        this.content.removeAll();
        this.content.add(content);
    }
}

The @Id annotation maps a component to an element in the TypeScript template on the client with the HTML identifiers "content" and "helloButton".
Vaadin creates a component instance of the declared type automatically and wires it to the template DOM element with the content and helloButton fields in the Java class.

Note	The declared type used in an `@Id` injection declaration must have a default constructor to instantiate it.

Note	The `Component` or `Element` must have the same `@Tag` as the actual element that’s referenced. This means that you can’t bind a `<span id="content"></span>` to a `@Id("content") Div content`.

Tip	The `@Id` annotation can also be used to inject an `Element` instance instead of a `Component` instance, if you want to use the lower-level `Element` API or there is no suitable HTML component available.

Example: Calling the setContent() method to set any Component as content for the MainPage class.

Source code

JavaMainPage page = new MainPage();
page.setContent(new Label("Hello!"));

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Docs

Docs

Binding to Template Components