react2github / java-mod-9-lab-2

Lab 2

Instructions

Using what you've learned about components and services, create a new component that will display the number of messages sent by the active user.

Here are a few hints:

1. Your new component can be positioned below the user message component at the bottom of the conversation history panel
2. It can be a simple label that shows the text "total message(s): " and then the number of messages sent by the active user
3. You already have a service that handles the sending of messages - integrate with that service to get your component access to the information it's looking for

Here is the solution:

1. In your messaging-data.service.ts, you already have a addUserMessage() function - no messages get sent through your application without going through this function.
2. Furthermore, that function already emits an event after it's done handling the requested message
3. So all we need to do in our new component is subscribe to the existing event and use the corresponding data to update a local variable with the active number of messages
4. We then simply use {{ }} notation to bind to that variable in our view

Here is the code for this solution:

Note: we used the following CLI command to generate the new component: ng g c application-component/conversation-history-component/message-count-component

• Inject the MessagingDataService into the message count component:

import { Component, OnInit } from "@angular/core";
import { MessagingDataService } from "src/app/messaging-data.service";
import { Message } from "src/app/message.model";

@Component({
  selector: "app-message-count-component",
  templateUrl: "./message-count-component.component.html",
  styleUrls: ["./message-count-component.component.css"],
})
export class MessageCountComponentComponent implements OnInit {
  sentMessageCount = 0;

  constructor(private messagingSvce: MessagingDataService) {}

  ngOnInit(): void {
    this.messagingSvce.userMessagesChanged.subscribe((messages: Message[]) => {
      this.sentMessageCount = messages.length;
    });
  }
}

• Add our simple text to the view for our message count component:

total message(s): {{ sentMessageCount }}

• Add the message count component to the conversation history component in conversation-history-comopnent.component.html:

<div class="container">
  <div class="row">
    <div class="col-12 p-3">Ludovic, Jessica</div>
  </div>
  <div class="row">
    <div class="col-12 border p-3">
      <app-conversation-thread-component></app-conversation-thread-component>
    </div>
  </div>
</div>

<div class="container">
  <div class="row">
    <div class="col-12 p-3">
      <app-send-message-component></app-send-message-component>
    </div>
  </div>
</div>

<div class="container">
  <div class="row">
    <div class="col-12 p-3">
      <app-message-count-component></app-message-count-component>
    </div>
  </div>
</div>

• Remove the message-count-component.component.spec.ts file, since we won't be writing unit tests for this component