Angular 6 - 通过服务从组件到消息组件传递消息 [英] Angular 6 - Passing messages via service to from component to message component

问题描述

我正在尝试如何从 app.component.ts 传递消息以显示在 messageComponent.ts

I am trying out how to pass a message from app.component.ts to be displayed in messageComponent.ts

在 app.component.html 上我添加了

on app.component.html I have added <app-messagecomponent></app-messagecomponent>

添加没有显示任何内容的时刻.

Add the moment it's just showing nothing.

我在服务中也有一个方法:

I also have a method in a service:

message.service.ts

message.service.ts

message(message) {
    return message;
}

那么我想通过消息服务传递来自其他组件的消息，以便它显示在 app-messagecomponent.html 中

So what I want to do to pass a message from other components via the message service so it's displaying in the app-messagecomponent.html

例如来自 app.component.ts:

For example from app.component.ts:

sendMessageToService() {
    this.myservice.message('my Message to be displayed in the messageComponent');
}

我该怎么做?

推荐答案

在这种情况下，要使用服务将消息从一个组件传递到另一个组件，您可以创建全局消息总线或事件总线(publish/订阅模式).

In this case to pass a message from one component to another component using a service , you can create a global message bus or event bus (publish/subscribe pattern).

为此，我们需要 Subject(使用 .next() 方法发出值)和 Observable(使用.subscribe() ) 来自 Rxjs，它现在是 angular 6 的重要组成部分.(对于这个例子，我使用 Rxjs 6 和 rxjs-compat 包)

For this we need the Subject (to emit values using .next() method) and Observable (to listen to the messages using .subscribe() ) from Rxjs which is now an essential part of angular 6. (For this example I am using Rxjs 6 along with rxjs-compat package)

在这里，我们将使用声明为 @Injectable 的 MessageService 类发送消息，以作为组件的依赖项注入.该消息将在 app.component.html 中单击按钮时发出.将在 message.component.ts 中检索相同的消息，以将其显示在 html 模板 message.component.html 中.我们将在 app.component.html 中包含 MessageComponent 的选择器，即 .

Here we will be sending a message using MessageService class which is declared as @Injectable to inject as a dependency in component. The message will be emitted on a button click from app.component.html . The same message will be retrieved in message.component.ts to show it in the html template message.component.html. We will include the selector for MessageComponent which is <app-messagecomponent></app-messagecomponent> in the app.component.html.

下面是完整的代码

message.service.ts

import { Injectable } from '@angular/core';
import { Observable,Subject} from 'rxjs';

@Injectable()
export class MessageService {
    private subject = new Subject<any>();

    sendMessage(message: string) {
        this.subject.next({ text: message });
    }

    clearMessage() {
        this.subject.next();
    }

    getMessage(): Observable<any> {
        return this.subject.asObservable();
    }
}

app.component.ts

import { Component } from '@angular/core';
import { MessageService } from './message.service';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent  {
  name = 'Angular 6';

  constructor(private service:MessageService){}

  sendMessage(): void {
        // send message to subscribers via observable subject
  this.service.sendMessage('Message from app Component to message Component!');   
  }

  clearMessage():void{
    this.service.clearMessage();
  }
}

app.component.html

<button (click)="sendMessage()">Click here to test message</button> <br><br>
<app-messagecomponent></app-messagecomponent>

message.component.ts

import { Component, OnDestroy } from '@angular/core';
import { Subscription } from 'rxjs';
import { MessageService } from './message.service';

@Component({
    selector: 'app-messagecomponent',
    templateUrl: 'message.component.html'
})

export class MessageComponent implements OnDestroy {
    message: any = {};
    subscription: Subscription;

    constructor(private messageService: MessageService) {
        // subscribe to app component messages
        this.subscription = this.messageService.getMessage().subscribe(message => { this.message = message; });
    }

    ngOnDestroy() {
        // unsubscribe to ensure no memory leaks
        this.subscription.unsubscribe();
    }
}

message.component.html

<p>The incoming message :  </p>  <br>
{{message?.text }}

这里我使用了 Elvis 操作符，以防 message 是 undefined .

Here I have used Elvis operator in case the message is undefined .

这是一个工作演示:https://stackblitz.com/edit/rxjs-snaghl

如果您正在寻找这样的东西，请告诉我.

Let me know if you are looking for something like this.

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