Angular · Theory

Services & DI

Theory

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Services & DI

Services & DI (and) is simple if you keep it on paper. Asha uses it for MarksService shared by two pages in the campus app.

Services & DI (and) order — meaning → @Injectable + constructor inject → one limit. Dumping ten features helps nobody.

Without Services & DI (and), the campus app gets messy and MarksService shared by two pages is hard to trust.

Services & DI (and) shows up in the campus app. Name MarksService shared by two pages, not “a real-world scenario”.

Services & DI (and) trap — new MarksService() in each component. Asha loses marks for that every viva.

Services & DI (and) is not a lonely heading. Asha ties it to MarksService shared by two pages.

One breath for Services & DI (and), then MarksService shared by two pages, then new MarksService() in each component. Sit down.

Diagram

  MarksPage ──inject──► MarksService
  ReportPage ──inject──► MarksService
  one root instance

Exam tip

For Services & DI (and): definition + the campus app + one failure.

Example

import { Component } from "@angular/core";

@Component({
  selector: "app-root",
  template: `
    <h1>{{ title }}</h1>
    <button (click)="toggle()">Toggle</button>
    <p *ngIf="open">Panel open</p>
  `,
})
export class AppComponent {
  title = "Angular practice";
  open = true;
  toggle() {
    this.open = !this.open;
  }
}

Services & DI: toggle open. Say whether the panel is on screen after one click.

Short notes

DefServices & DI (and) — Asha uses it for MarksService shared by two pages in the campus app.
RuleServices & DI (and) → @Injectable + constructor inject.
RememberServices & DI (and) + the Angular compiler (the campus app).
UseServices & DI (and) in the campus app (MarksService shared by two pages).
TrapServices & DI (and) — new MarksService() in each component.
ExServices & DI (and) → MarksService shared by two pages.

import { Component } from "@angular/core"; @Component({ selector: "app-root", template: ` <h1>{{ title }}</h1> <button (click)="toggle()">Toggle</button> <p *ngIf="open">Panel open</p> `, }) export class AppComponent { title = "Angular practice"; open = true; toggle() { this.open = !this.open; } }

Services & DI

Example

Short notes

Questions

Services & DI

Example

Short notes

Questions