Detailed examples of value transfer and communication methods between different components in Angular-headlines-php.cn

This article mainly introduces the methods of value transfer and communication between different components in Angular. The editor thinks it is quite good, so I will share it with you now and give it as a reference. Let’s follow the editor to take a look, I hope it can help everyone.

This article mainly introduces how Angular transfers values and communicates in different components. It is mainly divided into parent-child components and non-parent-child components.

Parameters and communication methods between parent and child components

Use event communication (EventEmitter, @Output):

Scenario: Yes To communicate between parent and child components, the child component is generally used to pass messages to the parent component;

Steps:

The child component creates an event EventEmitter object and uses @output to expose it Go out;
The parent component listens to the @output method of the child component, and then handles the event.

Code:

 // child 组件
  @Component({
   selector: &#39;app-child&#39;,
   template: &#39;&#39;,
   styles: [``]
  })
  export class AppChildComponent implements OnInit {
   @Output() onVoted: EventEmitter<any> = new EventEmitter();
   ngOnInit(): void {
    this.onVoted.emit(1);
   }
  }
  // parent 组件
  @Component({
   selector: &#39;app-parent&#39;,
   template: `
    <app-child (onVoted)="onListen($event)"></app-child>
   `,
   styles: [``]
  })
  export class AppParentComponent implements OnInit {
   ngOnInit(): void {
    throw new Error(&#39;Method not implemented.&#39;);
   }
   onListen(data: any): void {
    console.log(&#39;TAG&#39; + &#39;---------->>>&#39; + data);
   }
  }

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Using @ViewChild and @ViewChildren:

Scenario : Generally used for parent components to pass information to child components, or for parent components to call methods of child components;

Steps:

Use child components in parent components;
Use @ViewChild in the parent component to obtain the child component object.
The parent component uses the child component object to control the child component; (pass information or call methods).

Code:

// 子组件
@Component({
 selector: &#39;app-child&#39;,
 template: &#39;&#39;,
 styles: [``]
})
export class AppChildComponent2 implements OnInit {
  data = 1;
  ngOnInit(): void {
 }
 getData(): void {
  console.log(&#39;TAG&#39; + &#39;---------->>>&#39; + 111);
 }
}
// 父组件
@Component({
 selector: &#39;app-parent2&#39;,
 template: `
  <app-child></app-child>
 `,
 styles: [``]
})
export class AppParentComponent2 implements OnInit {
 @ViewChild(AppChildComponent2) child: AppChildComponent2;
 ngOnInit(): void {
  this.child.getData(); // 父组件获得子组件方法
  console.log(&#39;TAG&#39;+&#39;---------->>>&#39;+this.child.data);// 父组件获得子组件属性
 }
}

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Non-parent-child component parameter passing and communication method

Through routing parameters

Scenario: One component can jump to another component through routing, such as: list and edit

Steps:

A component jumps to B component through routerLink or router.navigate or router.navigateByUrl
##B component accepts these parameters

This method is only suitable for parameter transfer. Once the parameters between components are received, they will not change.

Code

Transfer method

routerLink

<a routerLink=["/exampledetail",id]></a>

routerLink=["/exampledetail",{queryParams:object}]

routerLink=["/exampledetail",{queryParams:&#39;id&#39;:&#39;1&#39;,&#39;name&#39;:&#39;yxman&#39;}];

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router.navigate

this.router.navigate([&#39;/exampledetail&#39;,id]);
this.router.navigate([&#39;/exampledetail&#39;],{queryParams:{&#39;name&#39;:&#39;yxman&#39;}});

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router.navigateByUrl

this.router.navigateByUrl(&#39;/exampledetail/id&#39;);
this.router.navigateByUrl(&#39;/exampledetail&#39;,{queryParams:{&#39;name&#39;:&#39;yxman&#39;}});

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Pass parameter After passing the parameters, the receiver has two receiving methods as follows:

snapshot

import { ActivateRoute } from &#39;@angular/router&#39;;
public data: any;
export class ExampledetailComponent implements OnInit { 
  constructor( public route: ActivateRoute ) { };
  ngOnInit(){
    this.data = this.route.snapshot.params[&#39;id&#39;];
  };
}

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queryParams

import { ActivateRoute } from &#39;@angular/router&#39;;
export class ExampledetailComponent implements OnInit { 
  public data: any;
  constructor( public activeRoute:ActivateRoute ) { };
  ngOnInit(){
    this.activeRoute.queryParams.subscribe(params => {
    this.data = params[&#39;name&#39;];
  });
};

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Use service Service to communicate, that is: two components inject a certain service at the same time

Scenario: The two components that need to communicate are not parent-child components or are not adjacent components; of course, also Can be any component.

Steps:

Create a new service, and component A and component B inject the service at the same time;
Component A starts from the service Obtain data, or want to transmit data to the service
Component B obtains data from the service, or wants to transmit data to the service.

Code:

  // 组件A
  @Component({
   selector: &#39;app-a&#39;,
   template: &#39;&#39;,
   styles: [``]
  })
  export class AppComponentA implements OnInit {
   constructor(private message: MessageService) {
   }
   ngOnInit(): void {
    // 组件A发送消息3
    this.message.sendMessage(3);
    const b = this.message.getMessage(); // 组件A接收消息；
   }
  }
  // 组件B
  @Component({
   selector: &#39;app-b&#39;,
   template: `
    <app-a></app-a>
   `,
   styles: [``]
  })
  export class AppComponentB implements OnInit {
   constructor(private message: MessageService) {
   }
   ngOnInit(): void {
    // 组件B获得消息
    const a = this.message.getMessage();
    this.message.sendMessage(5); // 组件B发送消息
   }
  }

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Message service module

Scenario: This involves A project needs to implement the possibility of communication between all components, or a component needs to communicate with several components, and parameters cannot be passed through routing.

Design method:

Use RxJs to define a service module MessageService, and all information is registered with the service;
Where you need to send a message, call the method of the service;
Use it where you need to receive information, call the method of receiving the information, obtain a Subscription object, and then monitor the information;
Of course, when each component is Destroyed,

this.subscription.unsubscribe();

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Code:

  // 消息中专服务
  @Injectable()
  export class MessageService {
   private subject = new Subject<any>();
   /**
   * content模块里面进行信息传输，类似广播
   * @param type 发送的信息类型
   *    1-你的信息
   *    2-你的信息
   *    3-你的信息
   *    4-你的信息
   *    5-你的信息
   */
   sendMessage(type: number) {
    console.log(&#39;TAG&#39; + &#39;---------->>>&#39; + type);
    this.subject.next({type: type});
   }
   /**
   * 清理消息
   */
   clearMessage() {
    this.subject.next();
   }
   /**
   * 获得消息
   * @returns {Observable<any>} 返回消息监听
   */
   getMessage(): Observable<any> {
    return this.subject.asObservable();
   }
  }
  // 使用该服务的地方，需要注册MessageService服务；
  constructor(private message: MessageService) {
  }
  // 消息接受的地方；
  public subscription: Subscription;
  ngAfterViewInit(): void {
    this.subscription = this.message.getMessage().subscribe(msg => {
     // 根据msg，来处理你的业务逻辑。
    })
   }

   // 组件生命周期结束的时候，记得注销一下，不然会卡；
   ngOnDestroy(): void {
    this.subscription.unsubscribe();
   }

   // 调用该服务的方法，发送信息；
   send():void {
    this.message.sendMessage(‘我发消息了，你们接受下&#39;); // 发送信息消息
   }

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The MessageService here is equivalent to using the broadcast mechanism to transfer information between all components; whether it is a number, a string, or an object, it can be transferred, and the propagation speed here is also quickly.

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