使用 firstUpdated () 无法正确显示

Question

我正在使用 vaadin 和 lit 实现一个复选框组件。我已经根据 vaadin 文档实现了它，但是我没有看到分组的复选框。

在控制台调试时，先调用“render()”，再调用“firstUpdated()”。所以我知道属性值将是一个空数组。

但是，我不明白为什么会发生这种情况，即使我像示例一样实现它。我怎样才能正确实施它？

这是自定义元素。

import { customElement, state } from 'lit/decorators.js';
import { html, LitElement } from 'lit';
import '@vaadin/vaadin-ordered-layout/vaadin-vertical-layout';
import '@vaadin/vaadin-checkbox/vaadin-checkbox-group'
import '@vaadin/vaadin-checkbox/vaadin-checkbox'
import { CheckboxElement } from '@vaadin/vaadin-checkbox';
import { Person } from '../../util/person';
import { getPeople } from '../../util/personUtil';


@customElement('checkbox-indeterminate')
export class CheckboxIndeterminate extends LitElement {
  @state()
  private items: Person[] = [];

  @state()
  private selectedIds: string[] = [];

  async firstUpdated() {
    this.items = await getPeople();
    this.selectedIds = [String(this.items[0].id), String(this.items[2].id)];
    console.log(`firstUpdated: ${JSON.stringify(this.items)}`);
    console.log(`firstUpdated: ${JSON.stringify(this.selectedIds)}`);
  }

  render() {
    console.log(`render: ${JSON.stringify(this.items)}`);
    console.log(`render: ${JSON.stringify(this.selectedIds)}`);
    return html`
      <vaadin-vertical-layout theme="spacing">
        <vaadin-checkbox
          .checked="${this.selectedIds.length === this.items.length}"
          .indeterminate="${this.selectedIds.length > 0 && this.selectedIds.length < this.items.length}"
          @change="${(e: Event) =>
            (this.selectedIds = (e.target as CheckboxElement).checked
              ? this.items.map((person) => String(person.id))
              : [])}"
        >
          Notify users
        </vaadin-checkbox>

        <vaadin-checkbox-group
          label="Users to notify"
          theme="vertical"
          .value="${this.selectedIds}"
          @value-changed="${(e: CustomEvent) => (this.selectedIds = e.detail.value)}"
        >
          ${this.items.map((person) => {
            return html`
              <vaadin-checkbox .value="${String(person.id)}">
                ${person.firstName} ${person.lastName}
              </vaadin-checkbox>
            `;
          })}
        </vaadin-checkbox-group>
      </vaadin-vertical-layout>
    `;
  }
}


declare global {
  interface HTMLElementTagNameMap {
    'checkbox-indeterminate': CheckboxIndeterminate;
  }
}

这是getPeople()方法。

import { Person } from './person';

export async function getPeople(): Promise<Person[]> {
  return [
    new Person(1, "Aria", "Bailey"),
    new Person(2, "Aaliyah", "Butler"),
    new Person(3, "Eleanor", "Price")
  ]
}

这是Personclass。

export class Person {
  id: number;
  firstName: string;
  lastName: string;

  constructor(id: number, firstName: string, lastName: string) {
    this.id = id;
    this.firstName = firstName;
    this.lastName = lastName;
  }
}

Answer 1

对不起。我找到了原因。我在 tsconfig.json 中犯了一个错误。我为目标指定了 ESNext，所以它没有输出到屏幕。

使用 firstUpdated () 无法正确显示

It is not displayed correctly with firstUpdated ()

vaadin

lit