Refresh the list by integrating information from the array

Greetings to All, I am currently working on a project to develop a small application that helps in managing tasks for employees. One of the features allows users to add a failed call attempt. However, I have encountered an issue where the new call object is not displayed in the view after adding it to the calls array within the CallService.

Here is the View Section

<mat-list>
<div mat-header style="color:#043755; font-weight: 700; font-size: 1.8rem; text-align: center;">Anrufe:</div>
<mat-list-item *ngFor="let call of calls;">
    <mat-icon mat-list-icon>phone</mat-icon>
    <div mat-line style="font-size: 1.2rem;">{{call.number}}</div>
    <div mat-line style="font-size: 1.2rem;"> {{call.date | date}} </div>
    <div mat-line style="font-size: 1.2rem; color:chocolate;">{{call.status}}</div>
</mat-list-item>

*The calls should be loaded using the ngFor directive.

This is the Component Code snippet

import {Component, OnInit} from '@angular/core';
import { Call, CallService } from '../call.service';


/**
 * @title List with sections
 */
@Component({
  selector: 'app-missed-calls',
  styleUrls: ['./missed-calls.component.css'],
  templateUrl: './missed-calls.component.html',
})
export class MissedCallsComponent implements OnInit {

  public calls: Call[] = [];

  constructor(private _callService: CallService) { }

  ngOnInit() {
    this.calls = this._callService.getCalls();
  }

}

I have injected the service and initialized my array during ngInit.

And here is the Service Implementation

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

export interface Call {
  number: string;
  date: Date;
  status: string;
}

@Injectable({
  providedIn: 'root'
})
export class CallService {

  constructor() { }

  calls: Call[] = [
    {number: '0677/61792248', 
    date: new Date('1/1/14'), 
    status: 'Verpasst'},
  ];

  getCalls() {
    return this.calls;
  }

  addCall(call: Call) {
    this.calls = [...this.calls, call];
  }

}

If anyone could offer assistance in resolving this issue, it would be greatly appreciated! :D

Answer №1

Quickfix Solution

If you make the Injectable public like this: public _callService: CallService, and update your ngFor loop as shown below, it should solve the issue:

<mat-list-item *ngFor="let call of _callService.calls;">

Another solution is to modify the addCall method with the following line:

this.calls.push(call)

The reason for these changes is explained further below.

Explanation

In JavaScript, objects are stored by reference, meaning they have unique internal IDs that point to memory locations. When you return this.calls, you are essentially sharing the same memory location where the object is stored.

By creating the calls object in the service and returning it, both the component's calls and the service's calls point to the same memory object. Any updates made to this object will be reflected in the ngFor loop.

Component.calls ->> js_id_123
Service.calls ->> js_id_123

However, when you use the spread operator in addCalls to create a new object, a new memory location is created and assigned to Service.calls.

[...this.calls, call]

As a result, the component and service no longer share the same memory object, causing the ngFor loop not to reflect any changes.

To resolve this issue, I recommend using push instead of destructuring for better performance, as it avoids recreating the whole array every time.

Performance Note

Destructuring can be slow with larger arrays, so using push is more efficient in adding elements without reiterating through the entire array.

If you have any questions, feel free to ask.

Proposed Solution

To improve performance, switch to using push in the service method. Additionally, consider making the service the sole source of truth to simplify your code structure.

Lastly, if the service does not require dependency injection or act as a traditional service, you can refactor it into a plain object named CallsManager. Initialize it within your component and utilize it directly in the ngFor loop.

Overall, this approach leads to cleaner code with a single source of truth and eliminates unnecessary complexities associated with services that don't rely on Dependency Injection.

Answer №2

You encountered an issue because you were not pushing new values, but simply assigning them to the array.

To fix this problem, modify your adding function as follows:

   // Change 

addCall(call: Call) {
    this.calls = [...this.calls, call];
  }

// To

addCall(call: Call) {
    this.calls.push(call)
  }

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