angular – Mat-table排序演示不工作

我试图让mat-table排序在本地工作,虽然我可以按预期显示数据,但点击标题行不会像在线示例那样进行排序(根本不会发生任何事情).
我想让这个演示在本地工作：
https://material.angular.io/components/sort/overview
https://plnkr.co/edit/XF5VxOSEBxMTd9Yb3ZLA?p=preview

我使用Angular CLI生成了一个新项目,然后按照以下步骤操作：
https://material.angular.io/guide/getting-started

这是我的本地文件：

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { MatSort,MatTableModule } from '@angular/material';

import { AppComponent } from './app.component';
import { TableSortingExample } from './table-sorting-example';

@NgModule({
  declarations: [
    AppComponent,TableSortingExample,MatSort
  ],imports: [
    BrowserModule,MatTableModule
  ],providers: [],bootstrap: [AppComponent]
})
export class AppModule { }

app.component.ts

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',templateUrl: './app.component.html',styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'app';
}

app.component.html

<div style="text-align:center">
  <h1>
    Welcome to {{title}}!
  </h1>
  <table-sorting-example></table-sorting-example>
</div>

表分拣example.html的

<div class="example-container mat-elevation-z8">
  <mat-table #table [dataSource]="dataSource" matSort>

    <!--- Note that these columns can be defined in any order.
          The actual rendered columns are set as a property on the row definition" -->

    <!-- ID Column -->
    <ng-container matColumnDef="userId">
      <mat-header-cell *matHeaderCellDef mat-sort-header> ID </mat-header-cell>
      <mat-cell *matCellDef="let row"> {{row.id}} </mat-cell>
    </ng-container>

    <!-- Progress Column -->
    <ng-container matColumnDef="progress">
      <mat-header-cell *matHeaderCellDef mat-sort-header> Progress </mat-header-cell>
      <mat-cell *matCellDef="let row"> {{row.progress}}% </mat-cell>
    </ng-container>

    <!-- Name Column -->
    <ng-container matColumnDef="userName">
      <mat-header-cell *matHeaderCellDef mat-sort-header> Name </mat-header-cell>
      <mat-cell *matCellDef="let row"> {{row.name}} </mat-cell>
    </ng-container>

    <!-- Color Column -->
    <ng-container matColumnDef="color">
      <mat-header-cell *matHeaderCellDef mat-sort-header> Color </mat-header-cell>
      <mat-cell *matCellDef="let row" [style.color]="row.color"> {{row.color}} </mat-cell>
    </ng-container>

    <mat-header-row *matHeaderRowDef="displayedColumns"></mat-header-row>
    <mat-row *matRowDef="let row; columns: displayedColumns;"></mat-row>
  </mat-table>
</div>


<!-- Copyright 2017 Google Inc. All Rights Reserved.
    Use of this source code is governed by an MIT-style license that
    can be found in the LICENSE file at http://angular.io/license -->

表分拣example.ts

import {Component,ViewChild} from '@angular/core';
import {DataSource} from '@angular/cdk/collections';
import {MatSort} from '@angular/material';
import {BehaviorSubject} from 'rxjs/BehaviorSubject';
import {Observable} from 'rxjs/Observable';
import 'rxjs/add/operator/startWith';
import 'rxjs/add/observable/merge';
import 'rxjs/add/operator/map';

/**
 * @title Table with sorting
 */
@Component({
  selector: 'table-sorting-example',styleUrls: ['table-sorting-example.css'],templateUrl: 'table-sorting-example.html',})
export class TableSortingExample {
  displayedColumns = ['userId','userName','progress','color'];
  exampleDatabase = new ExampleDatabase();
  dataSource: ExampleDataSource | null;

  @ViewChild(MatSort) sort: MatSort;

  ngOnInit() {
    this.dataSource = new ExampleDataSource(this.exampleDatabase,this.sort);
  }
}

/** Constants used to fill up our data base. */
const COLORS = ['maroon','red','orange','yellow','olive','green','purple','fuchsia','lime','teal','aqua','blue','navy','black','gray'];
const NAMES = ['Maia','Asher','Olivia','Atticus','Amelia','Jack','Charlotte','Theodore','Isla','Oliver','Isabella','Jasper','Cora','Levi','Violet','Arthur','Mia','Thomas','Elizabeth'];

export interface UserData {
  id: string;
  name: string;
  progress: string;
  color: string;
}

/** An example database that the data source uses to retrieve data for the table. */
export class ExampleDatabase {
  /** Stream that emits whenever the data has been modified. */
  dataChange: BehaviorSubject<UserData[]> = new BehaviorSubject<UserData[]>([]);
  get data(): UserData[] { return this.dataChange.value; }

  constructor() {
    // Fill up the database with 100 users.
    for (let i = 0; i < 100; i++) { this.addUser(); }
  }

  /** Adds a new user to the database. */
  addUser() {
    const copiedData = this.data.slice();
    copiedData.push(this.createNewUser());
    this.dataChange.next(copiedData);
  }

  /** Builds and returns a new User. */
  private createNewUser() {
    const name =
      NAMES[Math.round(Math.random() * (NAMES.length - 1))] + ' ' +
      NAMES[Math.round(Math.random() * (NAMES.length - 1))].charAt(0) + '.';

    return {
      id: (this.data.length + 1).toString(),name: name,progress: Math.round(Math.random() * 100).toString(),color: COLORS[Math.round(Math.random() * (COLORS.length - 1))]
    };
  }
}

/**
 * Data source to provide what data should be rendered in the table. Note that the data source
 * can retrieve its data in any way. In this case,the data source is provided a reference
 * to a common data base,ExampleDatabase. It is not the data source's responsibility to manage
 * the underlying data. Instead,it only needs to take the data and send the table exactly what
 * should be rendered.
 */
export class ExampleDataSource extends DataSource<any> {
  constructor(private _exampleDatabase: ExampleDatabase,private _sort: MatSort) {
    super();
  }

  /** Connect function called by the table to retrieve one stream containing the data to render. */
  connect(): Observable<UserData[]> {
    const displayDataChanges = [
      this._exampleDatabase.dataChange,this._sort.sortChange,];

    return Observable.merge(...displayDataChanges).map(() => {
      return this.getSortedData();
    });
  }

  disconnect() {}

  /** Returns a sorted copy of the database data. */
  getSortedData(): UserData[] {
    const data = this._exampleDatabase.data.slice();
    if (!this._sort.active || this._sort.direction == '') { return data; }

    return data.sort((a,b) => {
      let propertyA: number|string = '';
      let propertyB: number|string = '';

      switch (this._sort.active) {
        case 'userId': [propertyA,propertyB] = [a.id,b.id]; break;
        case 'userName': [propertyA,propertyB] = [a.name,b.name]; break;
        case 'progress': [propertyA,propertyB] = [a.progress,b.progress]; break;
        case 'color': [propertyA,propertyB] = [a.color,b.color]; break;
      }

      let valueA = isNaN(+propertyA) ? propertyA : +propertyA;
      let valueB = isNaN(+propertyB) ? propertyB : +propertyB;

      return (valueA < valueB ? -1 : 1) * (this._sort.direction == 'asc' ? 1 : -1);
    });
  }
}


/**  Copyright 2017 Google Inc. All Rights Reserved.
 Use of this source code is governed by an MIT-style license that
 can be found in the LICENSE file at http://angular.io/license */

有没有人知道为什么它会像在线表一样出现但缺乏排序功能？

imports: [
    BrowserModule,MatTableModule,MatSortModule
  ],