我们可以通过以下三种方式来实现：

1. 传递一个组件的引用给另一个组件
2. 通过子组件发送EventEmitter和父组件通信
3. 通过serive通信

1. 传递一个组件的引用给另一个组件

 Demo1 模板引用变量

模板引用变量通常用来引用模板中的某个 DOM 元素，它还可以引用 Angular 组件或指令或Web Component。 
使用井号 (#) 来声明引用变量。 #phone 的意思就是声明一个名叫 phone 的变量来引用 元素

这种方式适合组件间有依赖关系。 app component

<app-side-bar-toggle [sideBar]="sideBar"></app-side-bar-toggle>
<app-side-bar #sideBar></app-side-bar>

app.component.html

@Component({
  selector: 'app-side-bar-toggle',
  templateUrl: './side-bar-toggle.component.html',
  styleUrls: ['./side-bar-toggle.component.css']
})
export class SideBarToggleComponent {

  @Input() sideBar: SideBarComponent;

  @HostListener('click')
  click() {
    this.sideBar.toggle();
  }
}

side-bar-toggle.component.ts

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

  toggleSideBar(shouldOpen: boolean) {
    this.sideBarIsOpened = !this.sideBarIsOpened;
  }
}

 

2. 通过子组件发送EventEmitter和父组件通信

Demo2 这种方式利用事件传播，需要在子组件中写 app.component.html

<app-side-bar-toggle (toggle)="toggleSideBar()"></app-side-bar-toggle>
<app-side-bar [isOpen]="sideBarIsOpened"></app-side-bar>

app.component.ts

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

  toggleSideBar(shouldOpen: boolean) {
    this.sideBarIsOpened = !this.sideBarIsOpened;
  }
}

side-bar-toggle.component.ts

@Component({
  selector: 'app-side-bar-toggle',
  templateUrl: './side-bar-toggle.component.html',
  styleUrls: ['./side-bar-toggle.component.css']
})
export class SideBarToggleComponent {

  @Output() toggle: EventEmitter<null> = new EventEmitter();

  @HostListener('click')
  click() {
    this.toggle.emit();
  }
}

side-bar.component.ts

@Component({
  selector: 'app-side-bar',
  templateUrl: './side-bar.component.html',
  styleUrls: ['./side-bar.component.css']
})
export class SideBarComponent {

  @HostBinding('class.is-open') @Input()
  isOpen = false;
}

3. 通过service进行通信

Demo3 这里需要新建side-bar.service，我们把toggle方法写到service文件中， 然后将service注入到side-bar-toggle.component和side-bar-toggle.component，前者调用toggle方法，发送事件流，后者订阅事件

app.component.html

<app-side-bar-toggle></app-side-bar-toggle>
<app-side-bar></app-side-bar>

side-bar-toggle.component.ts

@Component({
  selector: 'app-side-bar-toggle',
  templateUrl: './side-bar-toggle.component.html',
  styleUrls: ['./side-bar-toggle.component.css']
})
export class SideBarToggleComponent {

  constructor(
    private sideBarService: SideBarService
  ) { }

  @HostListener('click')
  click() {
    this.sideBarService.toggle();
  }
}

side-bar.component.ts

@Component({
  selector: 'app-side-bar',
  templateUrl: './side-bar.component.html',
  styleUrls: ['./side-bar.component.css']
})
export class SideBarComponent {

  @HostBinding('class.is-open')
  isOpen = false;

  constructor(
    private sideBarService: SideBarService
  ) { }

  ngOnInit() {
    this.sideBarService.change.subscribe(isOpen => {
      this.isOpen = isOpen;
    });
  }
}

side-bar.service.ts

@Injectable()
export class SideBarService {

  isOpen = false;

  @Output() change: EventEmitter<boolean> = new EventEmitter();

  toggle() {
    this.isOpen = !this.isOpen;
    this.change.emit(this.isOpen);
  }
}