NG子组件未调用服务

// 服务类
import { Injectable } from '@angular/core';

@Injectable()
export class DataService {
  getData(): string {
    return 'Hello, World!';
  }
}

// 子组件
import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-child',
  template: `
    <div>{{ data }}</div>
  `,
})
export class ChildComponent {
  data: string;

  constructor(private dataService: DataService) {
    this.data = this.dataService.getData();
  }
}

// 模块
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { ChildComponent } from './child.component';
import { DataService } from './data.service';

@NgModule({
  imports: [BrowserModule],
  declarations: [ChildComponent],
  providers: [DataService],
  bootstrap: [ChildComponent],
})
export class AppModule {}