Comprehending Angular 5's Importing External Classes

I have developed a class structure for managing Schedules. I then brought in this class to my primary program. My issue arises from the fact that this class utilizes the HttpClient, which I was instructed to set up within the constructor. As a result, when I attempt to create a new instance of the Schedule (i.e., newSchedule = new Schedule;), it prompts me for a parameter instead of the HttpClient. How can I avoid specifying the HttpClient when creating a new object of the class?

Below is an example of the Schedule model class:

import { HttpClient } from '@angular/common/http';
export class Schedule {
    constructor(private httpClient: HttpClient) {}
}

However, now I am required to provide this.HttpClient within my main program, even though it is unnecessary:

import { HttpClient } from '@angular/common/http';
export class AppComponent {
    constructor(private httpClient: HttpClient) {}
    var NewSchedule = new Schedule(this.HttpClient);
}

How can I eliminate the necessity of passing this.HttpClient? It seems like there could be a flaw in my approach.

Answer №1

Your approach appears to be incorrect initially, but since you seek assistance, we are here to offer it.

To rectify the issue, you should consider making the constructor parameter optional. Here is how you can do it:

export class Schedule {
  constructor(private http?: HttpClient){}
}

If preferred, you may also assign a default value like this:

export class Schedule {
  constructor(private http: HttpClient = null){}
}

Answer №2

Upon reviewing the feedback, it seems that the goal is to create multiple instances of the Schedule class while maintaining access to the httpClient object.

One possible solution could be:

Add a public method within the Schedule class:

public getNewInstance(object: Object) {
    let obj = Object.create(object.constructor.prototype);
    object.constructor.apply(obj, [this.httpClient]);
    return obj;
}

Additionally, ensure that your Subject class is injectable. Keep in mind, your class will serve as an injectable and singleton within other classes, but you can still obtain multiple instances using that singleton.

Implement the following:

@Injectable()
export class Schedule ...

Next, in your appComponent, inject Subject.

export class AppComponent {
constructor(private subjectInstance: Subject) {}
...

private newSubjectInstance;
ngOnInit() {
    this.newSubjectInstance = this.subjectInstance.getNewInstance(this.subjectInstance);
    // This will result in a new instance with the httpClient retained inside.
}

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