构建一个复合组件

上一章，我们构建了第一个组件；本章我们将扩展所学内容，创建任务列表（TaskList），一个任务（Task）的列表。让我们将组件组合在一起，看看当引入更多复杂性时会发生什么。

任务列表

Taskbox 通过将置顶任务放在默认任务之上来强调它们。它产生了 TaskList 的两种变体，你需要为它们创建故事：默认和置顶项。

由于 Task 数据可以异步发送，我们还需要一个在没有连接时渲染的加载状态。此外，当没有任务时，我们需要一个空状态。

准备就绪

复合组件与它所包含的基本组件并没有太大区别。创建一个TaskList组件和一个配套的故事文件：src/app/components/task-list.component.ts和src/app/components/task-list.stories.ts。

从 TaskList 的粗略实现开始。你需要导入之前的 Task 组件，并将属性和操作作为输入传递。

import type { TaskData } from '../types';

import { CommonModule } from '@angular/common';
import { Component, Input, Output, EventEmitter } from '@angular/core';

import { TaskComponent } from './task.component';

@Component({
  selector: 'app-task-list',
  standalone: true,
  imports: [CommonModule, TaskComponent],
  template: `
    <div class="list-items">
      <div *ngIf="loading">loading</div>
      <div *ngIf="!loading && tasks.length === 0">empty</div>
      <app-task
        *ngFor="let task of tasks"
        [task]="task"
        (onArchiveTask)="onArchiveTask.emit($event)"
        (onPinTask)="onPinTask.emit($event)"
      >
      </app-task>
    </div>
  `,
})

export class TaskListComponent {
  /**
   * The list of tasks
   */
  @Input() tasks: TaskData[] = [];

  /**
   * Checks if it's in loading state
   */
  @Input() loading = false;

  /**
   * Event to change the task to pinned
   */
  @Output()
  onPinTask = new EventEmitter<Event>();

  /**
   * Event to change the task to archived
   */
  @Output()
  onArchiveTask = new EventEmitter<Event>();
}

接下来，在故事文件中创建 Tasklist 的测试状态。

import type { Meta, StoryObj } from '@storybook/angular';

import { componentWrapperDecorator } from '@storybook/angular';

import { TaskListComponent } from './task-list.component';

import * as TaskStories from './task.stories';

export const TaskListData = [
  { ...TaskStories.TaskData, id: '1', title: 'Task 1' },
  { ...TaskStories.TaskData, id: '2', title: 'Task 2' },
  { ...TaskStories.TaskData, id: '3', title: 'Task 3' },
  { ...TaskStories.TaskData, id: '4', title: 'Task 4' },
  { ...TaskStories.TaskData, id: '5', title: 'Task 5' },
  { ...TaskStories.TaskData, id: '6', title: 'Task 6' },
]

const meta: Meta<TaskListComponent> = {
  component: TaskListComponent,
  title: 'TaskList',
  tags: ['autodocs'],
  excludeStories: /.*Data$/,
  decorators: [
    //👇 Wraps our stories with a decorator
    componentWrapperDecorator(
      (story) => `<div style="margin: 3em">${story}</div>`
    ),
  ],
  args: {
    ...TaskStories.TaskData.events,
  },
};


export default meta;
type Story = StoryObj<TaskListComponent>;

export const Default: Story = {
  args: {
    tasks: TaskListData,
  },
}

export const WithPinnedTasks: Story = {
  args: {
    // Shaping the stories through args composition.
    // Inherited data coming from the Default story.
    tasks: [
      // Shaping the stories through args composition.
      // Inherited data coming from the Default story.
      ...(Default.args?.tasks?.slice(0, 5) || []),
      { id: '6', title: 'Task 6 (pinned)', state: 'TASK_PINNED' },
    ],
  },
}


export const Loading: Story = {
  args: {
    tasks: [],
    loading: true,
  },
}

export const Empty: Story = {
  args: {
    // Shaping the stories through args composition.
    // Inherited data coming from the Loading story.
    ...Loading.args,
    loading: false,
  },
}

通过导入 TaskStories，我们能够以最小的努力 组合 我们故事中的参数（简称 args）。这样，两个组件都期望的数据和操作（模拟的回调）都能得到保留。

现在在 Storybook 中检查新的 TaskList 故事。

构建状态

我们的组件仍然很粗糙，但现在我们对要努力实现的故事有了一些想法。你可能会认为 .list-items 包装器过于简单。你是对的——在大多数情况下，我们不会创建一个新组件只是为了添加一个包装器。但是 TaskList 组件的真正复杂性体现在边缘情况 withPinnedTasks、loading 和 empty 中。

import type { TaskData } from '../types';

import { CommonModule } from '@angular/common';
import { Component, Input, Output, EventEmitter } from '@angular/core';

import { TaskComponent } from './task.component';

@Component({
  selector: 'app-task-list',
  standalone: true,
  imports: [CommonModule, TaskComponent],
  template: `
    <div class="list-items">
      <app-task
        *ngFor="let task of tasksInOrder"
        [task]="task"
        (onArchiveTask)="onArchiveTask.emit($event)"
        (onPinTask)="onPinTask.emit($event)"
      >
      </app-task>
      <div
        *ngIf="tasksInOrder.length === 0 && !loading"
        class="wrapper-message"
        data-testid="empty"
      >
        <span class="icon-check"></span>
        <p class="title-message">You have no tasks</p>
        <p class="subtitle-message">Sit back and relax</p>
      </div>
      <div *ngIf="loading">
        <div *ngFor="let i of [1, 2, 3, 4, 5, 6]" class="loading-item">
          <span class="glow-checkbox"></span>
          <span class="glow-text"> <span>Loading</span> <span>cool</span> <span>state</span> </span>
        </div>
      </div>
    </div>
  `,
})
export class TaskListComponent {
  /**
   * @ignore
   * Component property to define ordering of tasks
   */
  tasksInOrder: TaskData[] = [];

  /**
   * Checks if it's in loading state
   */
  @Input() loading = false;

  /**
   * Event to change the task to pinned
   */
  @Output()
  onPinTask = new EventEmitter<Event>();

  /**
   * Event to change the task to archived
   */
  @Output()
  onArchiveTask = new EventEmitter<Event>();

  /**
   * The list of tasks
   */
  @Input()
  set tasks(arr: TaskData[]) {
    const initialTasks = [
      ...arr.filter((t) => t.state === 'TASK_PINNED'),
      ...arr.filter((t) => t.state !== 'TASK_PINNED'),
    ];
    const filteredTasks = initialTasks.filter(
      (t) => t.state === 'TASK_INBOX' || t.state === 'TASK_PINNED'
    );
    this.tasksInOrder = filteredTasks.filter(
      (t) => t.state === 'TASK_INBOX' || t.state === 'TASK_PINNED'
    );
  }
}

添加的标记会产生以下 UI

注意置顶项在列表中的位置。我们希望置顶项渲染在列表的顶部，以优先显示给用户。