Angular 5
When is a service created and destroyed, what are its lifecycle hooks (if any) and how is its data shared between components?
EDIT: To clarify, this is NOT a question about the lifecycle of components. This question is about the lifecycle of services. In case a service does not have a lifecycle, how is the flow of data between components and services managed?
Lifecycle hooks are a special functionality in Angular that allow us to “hook into” and run code at a specific lifecycle event of a component or directive. Angular manages components and directives for us when it creates them, updates them, or destroys them.
Component Lifecycle. A component has a lifecycle managed by Angular itself. Angular manages creation, rendering, data-bound properties etc. It also offers hooks that allow us to respond to key lifecycle events.
There are eight lifecycle hooks in Angular: ngOnChanges() ngOnInit() ngDoCheck()
Service can have 2 scopes.
If service is declared on your module, you have same instance shared for all, this means service will be constructed when the first component/directive/service/Pipe who needs it will be created. Then it will be destroyed when Module itself will be destroyed (most of the time when page is unloaded)
if the service is declared on Component/Directive/Pipe, then 1 instance will be created each time when Component/Directive/Pipe will be created and destroyed when related Component/Directive/Pipe will be destroyed.
You can see it in action
Code testing : 2 services are made for showing when they are created/destroyed.
@NgModule({ providers: [GlobalService] // This means lifeCycle is related to the Module, and only one instance is created for the whole module. It will be created only when the first element who needs it will be created. }) export class AppModule { }
Second service is a local component service and will be create for each hello-component
instance created, and will be destroyed just before hello-component
will be destroyed.
@Injectable() export class LocalService implements OnDestroy{ constructor() { console.log('localService is constructed'); } ngOnDestroy() { console.log('localService is destroyed'); } } @Component({ selector: 'hello', template: `<h1>Hello {{name}}!</h1>`, styles: [`h1 { font-family: Lato; }`], providers: [LocalService] }) export class HelloComponent implements OnInit, OnDestroy { @Input() name: string; constructor(private localService: LocalService, private globalService: GlobalService) {} ngOnInit(){ console.log('hello component initialized'); } ngOnDestroy() { console.log('hello component destroyed'); } }
As you can see, Service
in angular can have OnDestroy
life cycle hook.
Services only live inside the scope of their providers, so in the scope of a module or a single component. They are instantiated when injected for the first time and keept alive as long as the provider exists.
As services are normal classes, angulars lifecycle hooks do not apply to them.
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