Is it possible to execute some code when a service is initialized. For example when the service product Service is initialized I would want to execute this code:
this.var = this.sharedService.aVar;
Other than constructor there is NO lifecycle hooks for Service..
Lifecycle hooks are supported by component/directive
Injectables are normal classes (normal objects) and as such, they have no special lifecycle.
#Injectable()
export class SampleService {
constructor() {
console.log('Sample service is created');
//Do whatever you need when initialized.
}
}
the class’s constructor is called, so that’s what your “OnInit” would be. As for the destruction, a service does not really get destroyed.
where a service needs another service use dependency injection
#Injectable()
export class HeroService {
private yourVariable: any;
constructor(private sharedService: sharedService) {
this.yourVariable = this.sharedService.aVar;
}
I suggest you read up a little on lifecycle hooks in Angular. While in the constructor is an option it is a good idea to keep the code in that limited to variable initialization and use the ngOnInit lifecycle hook to do class initialization work. Both are an option but understanding the lifecycle hooks is a good starting point in addressing your question and thinking through where you want to do this.
Related
I'm using inversify with inversify-express-utils.
I have a quite usual inversify/express setup.
Controller
Service
A module
B module
B module is a class that looks like this:
import { injectable } from 'inversify';
import SpellCorrector from 'spelling-corrector';
#injectable()
export class SpellCorrectorFactory {
private corrector: any;
constructor() {
this.corrector = new SpellCorrector();
this.corrector.loadDictionary();
}
public correct = (text: string): string => this.corrector.correct(text);
}
Now, the problem here is that as you can see in the constructor, I have this line of code:
this.corrector.loadDictionary()
This line takes over a second to execute.
So basically it seems like the actual instance creation is happening when I #inject service B to service A
So every time I make a request, the constructor of SpellCorrectorFactory is being executed, so the request takes over 1000ms instead of below 100ms.
How can I bind this class to inversify so that during binding the class is being instantiated and in the A module I have access to the instance which was created on app start, and not when I send a request to the express path?
Thanks in advance!
Ok, just in case someone looks at this page in search for an answer.
The solution is as simple as:
container
.bind<SpellCorrectorFactory>(TYPES.SpellCorrector)
.to(SpellCorrectorFactory)
.inSingletonScope();
This calls the constructor of the SpellCorrectorFactory immediately and returns the instance.
So whenever you inject the result of this binding you have direct access to the instance and its functions.
I've got a service that I use to share data between 2 components. That part works flawlessly, but now I need to call a method of component A, when something triggers on the service (and pass a value to that component). How can I do this? I read on older questions that this is a wrong approach but since Im a noob I dont know what to search for a solution.
Do I need to use observables?
I think Joseph's idea is the way to go.
Here's how I'd implement it:
class FooService {
private _newEvents = new Subject();
newEvents$ = this._newEvents.asObservable();
addNewEvent (ev) {
this._newEvents.next(e);
}
}
// Allow `A` class to communicate with `B` class
class A {
addEvent (ev) {
this.fooService.addNewEvent(ev);
}
}
class B {
private subscription: Subscription;
ngOnInit () {
this.subscription = this.fooService.newEvents$
.subscribe(e => {})
}
ngOnDestroy () {
this.subscription.unsubscribe();
}
}
Note that if your B class subscribes to multiple observables, you should unsubscribe from them using, among other solutions, takeUntil.
Observables / Subjects are one way. You would have one Subject in the service, and would use .next(value) on it to exchange values. Each component which is interested in the value may subscribe to that subject.
Example: (taken from RxJS docs
//your Service
import { Subject } from 'rxjs';
const subject = new Subject<number>();
//Component A (and others as well)
service.subject.subscribe({
next: (num) => console.log(num)
});
//this should work as well with prettier syntax:
service.subject.subscribe(sum =>
console.log(num)
);
//Component B
service.subject.next(7) //passing number 7 to Component A
Whenever you create a subscription, make sure to always unsubscribe! Else you might end up with stacks of subscriptions, which will all get triggered simultaneously in the very same component.
From personal experience, I found it more helpful to outsource any functions and variables that could be considered as global into a dedicated service, if possible. If you directly read the variables of a service from your components (and modify them if necessary), you'll have the same effect. That works as long as you keep a proper service structure. Some examples of dedicated services with global use are:
Translations (TranslationService)
Rights Management (PermissionService)
Take this code for example:
#Component({
selector: 'some-chart',
template: '<div></div>,
})
class ChartingThing implements OnInit {
mySubscription: Subscription = new Subscription();
ngOnInit() {
this.mySubscription.subscribe((blah) => {
console.log(blah);
});
}
}
When Angular cleans up this component, will that automatically destroy the subscription? Or do I need to call this.mySubscription.unsubscribe() in an ngOnDestroy method? I could see needing to call unsubscribe if Angular is caching components or something of that nature.
This is not the same as: Angular/RxJs When should I unsubscribe from `Subscription`
In every example there, they're talking about unsubscribing from an injected service. That makes sense to do since the service isn't necessarily going to be destroyed just because the component is destroyed.
Here, I am clearly referencing a subject created by this class. I want to know if mySubscription needs to be completed in ngOnDestroy or if it gets cleaned up because the class is destroyed and the mySubscription property would get destroyed with it or something else entirely.
Another Observable question.
I'm working with angular translation service and Kendo.UI components.
According to the Kendo.UI documentation, I can implement a MessageService to translate its components.
To do so, I have to extend an abstract class that contains a method that return a string:
#Injectable()
export class MyMessageService extends MessageService {
private messages = {'kendo.upload.select': 'initial value'}
constructor(private readonly translate: TranslateService) {
super();
this.translate.get('my_translation_key')
.subscribe((value) => {
this.messages['kendo.upload.select'] = value;
});
}
public get(key: string): string {
return this.messages[key];
}
}
The problem is, the moment kendo injects my custom service, the observables were not resolved yet and my button never get its value changed from "'initial value'" to the translated.
From my understatement, kendo's service should accept an observable, not a string. But I'm not very familiar with promises/subjects/observables.
Is there a workaround for this?
ps.: I know TranslateService has a .instant(key) method, but the same way, the values are not loaded yet.
It sounds like you are saying it the observable is pushed before kendo subscribes. If that is the case then you should use a ReplaySubject instead of an Observable as the Replaysubject will push all the values that were given to the observable to the subscriber when it subscribes.You can tell it how many observed values to replay.
Also you could try instead to call your server after view init or even OnInint. Calling the service in the constructor is not recommended as the view is not done rendering and any html async pipes may not be set yet. Worst case you can use the Replay subject.
I am currently working on porting a Backbone project to an Angular 2 project (obviously with a lot of changes), and one of the project requirements requires certain methods to be accessible publicly.
A quick example:
Component
#component({...})
class MyTest {
private text:string = '';
public setText(text:string) {
this.text = text;
}
}
Obviously, I could have <button (click)="setText('hello world')>Click me!</button>, and I would want to do that as well. However, I'd like to be able to access it publicly.
Like this
<button onclick="angular.MyTest.setText('Hello from outside angular!')"></click>
Or this
// in the js console
angular.MyTest.setText('Hello from outside angular!');
Either way, I would like the method to be publicly exposed so it can be called from outside the angular 2 app.
This is something we've done in backbone, but I guess my Google foo isn't strong enough to find a good solution for this using angular.
We would prefer to only expose some methods and have a list of public apis, so if you have tips for doing that as well, it'd be an added bonus. (I have ideas, but others are welcomed.)
Just make the component register itself in a global map and you can access it from there.
Use either the constructor or ngOnInit() or any of the other lifecycle hooks to register the component and ngOnDestroy() to unregister it.
When you call Angular methods from outside Angular, Angular doesn't recognize model change. This is what Angulars NgZone is for.
To get a reference to Angular zone just inject it to the constructor
constructor(zone:NgZone) {
}
You can either make zone itself available in a global object as well or just execute the code inside the component within the zone.
For example
calledFromOutside(newValue:String) {
this.zone.run(() => {
this.value = newValue;
});
}
or use the global zone reference like
zone.run(() => { component.calledFromOutside(newValue); });
https://plnkr.co/edit/6gv2MbT4yzUhVUfv5u1b?p=preview
In the browser console you have to switch from <topframe> to plunkerPreviewTarget.... because Plunker executes the code in an iFrame. Then run
window.angularComponentRef.zone.run(() => {window.angularComponentRef.component.callFromOutside('1');})
or
window.angularComponentRef.zone.run(() => {window.angularComponentRef.componentFn('2');})
This is how i did it. My component is given below. Don't forget to import NgZone. It is the most important part here. It's NgZone that lets angular understand outside external context. Running functions via zone allows you to reenter Angular zone from a task that was executed outside of the Angular zone. We need it here since we are dealing with an outside call that's not in angular zone.
import { Component, Input , NgZone } from '#angular/core';
import { Router } from '#angular/router';
#Component({
selector: 'example',
templateUrl: './example.html',
})
export class ExampleComponent {
public constructor(private zone: NgZone, private router: Router) {
//exposing component to the outside here
//componentFn called from outside and it in return calls callExampleFunction()
window['angularComponentReference'] = {
zone: this.zone,
componentFn: (value) => this.callExampleFunction(value),
component: this,
};
}
public callExampleFunction(value: any): any {
console.log('this works perfect');
}
}
now lets call this from outside.in my case i wanted to reach here through the script tags of my index.html.my index.html is given below.
<script>
//my listener to outside clicks
ipc.on('send-click-to-AT', (evt, entitlement) =>
electronClick(entitlement));;
//function invoked upon the outside click event
function electronClick(entitlement){
//this is the important part.call the exposed function inside angular
//component
window.angularComponentReference.zone.run(() =
{window.angularComponentReference.componentFn(entitlement);});
}
</script>
if you just type the below in developer console and hit enter it will invoke the exposed method and 'this works perfect ' will be printed on console.
window.angularComponentReference.zone.run(() =>
{window.angularComponentReference.componentFn(1);});
entitlement is just some value that is passed here as a parameter.
I was checking the code, and I have faced that the Zone is not probably necessary.
It works well without the NgZone.
In component constructor do this:
constructor(....) {
window['fncIdentifierCompRef'] = {
component = this
};
}
And in the root script try this:
<script>
function theGlobalJavascriptFnc(value) {
try {
if (!window.fncIdentifierCompRef) {
alert('No window.fncIdentifierCompRef');
return;
}
if (!window.fncIdentifierCompRef.component) {
alert('No window.fncIdentifierCompRef.component');
return;
}
window.fncIdentifierCompRef.component.PublicCmpFunc(value);
} catch(ex) {alert('Error on Cmp.PublicCmpFunc Method Call')}
}
</script>
This works to me.
The problem is that Angular's components are transpiled into modules that aren't as easy to access as regular JavaScript code. The process of accessing a module's features depends on the module's format.
An Angular2 class can contain static members that can be defined without instantiating a new object. You might want to change your code to something like:
#component({...})
class MyTest {
private static text: string = '';
public static setText(text:string) {
this.text = text;
}
}
Super simple solution!! save component or function with an alias outside
declare var exposedFunction;
#Component({
templateUrl: 'app.html'
})
export class MyApp {
constructor(public service:MyService){
exposedFunction = service.myFunction;
}
at index.html add in head
<script>
var exposedFunction;
</script>
Inside exposed function do not use this. parameters if you need them you will have to use closures to get it to work
This is particularly useful in ionic to test device notifications on web instead of device