Cad iad na hooks saolré an chomhpháirt sa Angular?

Question

Accepted Answer

**Lifecycle hooks** ar dhóigh iad a ghlaonn Angular ag nóiméid shonracha i saol an chomhpháirt — cruthú, athruithe ionchur, rindreáil agus scriosadh. Cuireann tú i bhfeidhm iad trí mhéhodanna comhéadain a chur le do rang comhpháirt.

## The main hooks in order

```ts
import { Component, OnInit, OnDestroy, OnChanges, SimpleChanges } from "@angular/core";

@Component({ ... })
export class MyComponent implements OnInit, OnDestroy, OnChanges {
  ngOnChanges(changes: SimpleChanges) {
    // called when an @Input value changes (before ngOnInit the first time)
  }
  ngOnInit() {
    // called ONCE after the first ngOnChanges — do initialization, fetch data
  }
  ngOnDestroy() {
    // called just before the component is removed — CLEAN UP here
  }
}
```

## The full sequence

```text
constructor          → DI happens; inputs NOT yet available
ngOnChanges          → when @Input values are set/changed
ngOnInit             → once, after first ngOnChanges ★ (init, fetch data)
ngDoCheck            → every change detection run (custom change detection)
ngAfterContentInit   → projected content (<ng-content>) initialized
ngAfterViewInit      → the component's view + child views ready ★ (access @ViewChild)
ngAfterViewChecked   → after each view check
ngOnDestroy          → before removal ★ (unsubscribe, clear timers)
```

## The three you use most

```ts
ngOnInit() {
  this.userService.getUsers().subscribe(u => this.users = u); // init/fetch — inputs are ready
}
ngAfterViewInit() {
  this.chart.nativeElement.focus(); // the DOM/@ViewChild exists now
}
ngOnDestroy() {
  this.subscription.unsubscribe();   // prevent memory leaks!
  clearInterval(this.timer);
}
```

- **`ngOnInit`** — an áit dhian do thúsú agus soláthru sonraí (murab ionann agus an tógálaí, tá `@Input`s ar fáil anseo).
- **`ngAfterViewInit`** — nuair a bhíonn amhairc leanaí agus tagairtí `@ViewChild` ann.
- **`ngOnDestroy`** — glanadh: díliostáil ó Observables, soiléir-scuab timthriallach, baint ghabhálaithe.

## Why ngOnInit over the constructor

Ní ba chóir don tógálaí ach DI a dhéanamh; níl ionchur ceangailte go fóill ann. Ritheann `ngOnInit` tar éis do Angular an chomhpháirt agus a ionchur a chur ar bun — an áit cheart do dhramhchloghaol thosaigh.

## Cén fáth a bhíonn tábhacht ann

Ligean do na lifecycle hooks duit loighic a rith san am ceart — tús a chur in `ngOnInit`, rochtain ar an bhfísean ghnóthaithe in `ngAfterViewInit`, agus go háirithe **glanadh in `ngOnDestroy`** (díliostáil ó Observables an bealach #1 chun dríochar cuimhne a sheachaint in Angular).

Tá eolas ar an ord agus ar ról gach hook riachtanach do shóláthru sonraí cheart, rochtain DOM agus bainistiú acmhainne.