Mene ne angular lifecycle hooks na na abin?

Question

Accepted Answer

**Lifecycle hooks** ayyuka ne da Angular ke kira a lokuta na takaici a rayuwa na abin — kirkira, sauye shi da ajiya, zane, da hallaka. Kuna aiwatar da su ta hanyar ƙara hanyoyin jikawa zuwa aji ƙungiyar abin.

## 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`** — wurin daidai don girma da kuma dawo da bayani (ba kamar ma'amala ba, `@Input`s suna samuwa a nan).
- **`ngAfterViewInit`** — lokacin da yake jiya da ƙananan gida da `@ViewChild` sanannun.
- **`ngOnDestroy`** — tsaftacewa: rashin bayyanewa daga Observables, share tuluka, cirewa makinai.

## Why ngOnInit over the constructor

Kunna ma'amala ya kamata kawai DI ne; bayyanewa ba tano ba a nan. `ngOnInit` yana gudana bayan Angular ya shimfiɗi abin da ingantun bayyanewa — fadadalin waje don girma.

## Me shi ya kakaita

Lifecycle hooks suna ba ku damar gudana dabari a lokuta daidai — girma a `ngOnInit`, samun gida jiya a `ngAfterViewInit`, da muhimmin gida **tsaftacewa a `ngOnDestroy`** (rashin bayyanewa daga Observables shine hanyar #1 don guje wa abin watsa ajiya a Angular).

Sanin jari da waje na kowane hook ya zama mahimmanci don samun bayani daidai, samun gida DOM, da sarrafa albarkatun.