Observer callback is not invoked when using rxjs interval - javascript

I have this method:
export class PeriodicData {
public checkForSthPeriodically(): Subscription {
return Observable.interval(10000)
.subscribe(() => {
console.log('I AM CHECKING');
this.getData();
});
};
public getData(): Observable<MyObject> {
let objects: MyObject[] = this.filterData();
return Observable.from(objects);
}
public filterData(): MyObject[] {
let someData;
// someData = filter(...) // logic to filter data
return someData;
}
}
Now I subscribe to getData() in another class:
class Another {
constructor(private periodicData: PeriodicData ) {
this.periodicData.getData().subscribe(obj => {
console.log('IN ANOTHER CLASS');
});
}
}
This is not working. The "IN ANOTHER CLASS" is not being logged. Am I missing something ?

If you tested this only with live TypeScript transpiler, then it doesn't throw an error when you don't specifically include Observable and the from operator (even though I don't know why).
I added to the top of app.component.ts and it works now:
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/from';
See your demo on plnkr.co: http://plnkr.co/edit/uVnwG3bo0N8ZkrAgKp7F

Related

Rxjs using first() with timer()

i'm trying to call a service every 10seconds but also want to execute some code only on the first emission, the problem here is that the first entry is duplicated, here is the code :
ionViewWillEnter() {
this.isLoading = true;
const Obs = timer(0, 10000).pipe(
switchMap(() => {
return this.serviceName.someFunc();
})
);
this.timerSub = Obs.subscribe();
this.timerSub = Obs.pipe(first()).subscribe(() => {
this.isLoading = false;
});
}
i also noticed another problem which is that even though i unsubscribe when i leave the page, the service is still being called every 10 seconds, any help is appreciated.
UPDATE
i found a solution, but it's more of a workaround, basically what i did was put a setTimeout on the subscription :
this.timerSub = Obs.pipe(first()).subscribe(() => {
this.isLoading = false;
});
setTimeout(() => {
this.timerSub = Obs.subscribe();
}, 10000);
and apparently the unsubscribe problem was solved as well, although i would appreciate the feedback with some more elegant solutions, thanks in advance.
The answer provided by Nilesh Patel should work fine, but I still wanted to add this answer to share some minor tips and improvements that you may need to use in your app.
Please take a look at this Stackblitz demo.
The first thing to notice is that if you're using the timer operator and you're interested in doing something the first time it emits, you can check the value returned by that operator and see if it's 0:
timer(0, 10000).pipe(
tap(currentTimer => {
if (currentTimer === 0) {
this.someFunctionToRunOnlyOnce();
}
}),
// ...
);
The second thing to keep in mind is that instead of storing every subscription in a variable (to then unsubscribe from all of them) you can create a subject and use the takeUntil operator like this:
private unsubscribe$: Subject<void> = new Subject<void>();
// ...
timer(0, 10000).pipe(
// ... other operators
takeUntil(this.unsubscribe$) // <-- like this
).subscribe();
// ...
ngOnDestroy() {
this.unsubscribe$.next(); // <-- this will clean the streams
this.unsubscribe$.unsubscribe(); // <-- this will clean the unsubscribe$ stream
}
And another very minor thing to keep in mind is that you can "pause" and "resume" the stream whenever you want without "destroying" it. For example, you can pause it when leaving the page and then resume it again when the user is about to enter to the page again by using the filter operator:
private isInPage: boolean = true;
// ...
timer(0, 10000).pipe(
filter(() => this.isInPage),
// other operators ...
);
// ...
ionViewWillEnter() {
this.isInPage = true;
}
ionViewWillLeave() {
this.isInPage = false;
}
So putting all that together it'd be something like this:
import { Component, OnInit } from "#angular/core";
import { NavController } from "#ionic/angular";
import { Observable, of, Subject, timer } from "rxjs";
import { delay, filter, switchMap, takeUntil, tap } from "rxjs/operators";
#Component({
selector: "app-home",
templateUrl: "./home.page.html",
styleUrls: ["./home.page.scss"]
})
export class HomePage implements OnInit {
private isInPage: boolean = true;
private unsubscribe$: Subject<void> = new Subject<void>();
constructor(private navCtrl: NavController) {}
ngOnInit() {
timer(0, 10000)
.pipe(
filter(() => this.isInPage),
tap(currentTimer => {
if (currentTimer === 0) {
this.someFunctionToRunOnlyOnce();
}
}),
switchMap(() => {
return this.someAsynFunction();
}),
takeUntil(this.unsubscribe$)
)
.subscribe();
}
ionViewWillEnter() {
this.isInPage = true;
}
ionViewWillLeave() {
this.isInPage = false;
}
ngOnDestroy() {
this.unsubscribe$.next();
this.unsubscribe$.unsubscribe();
}
public openDetailsPage(): void {
this.navCtrl.navigateForward("details");
}
private someAsynFunction(): Observable<number> {
const randomNumber = Math.floor(Math.random() * 10000) + 1;
console.log("==> Running someAsynFunction method");
return of(randomNumber).pipe(delay(1000));
}
private someFunctionToRunOnlyOnce(): void {
console.log("==> Running someAsynFunctionToRunOnlyOnce method");
}
}
better solution:
create variable firstSub at the the top.
ionViewWillEnter() {
this.isLoading = true;
this.timerSub = timer(0, 10000).pipe(
switchMap(() => {
return this.serviceName.someFunc();
})
);
this.firstSub = this.timerSub.pipe(first());
this.firstSub.subscribe(() => {
// only emit once(first)
this.isLoading = false;
});
}
unsubscribing before component view destroyed.
ngOnDestroy(){
this.timerSub.unsubscribe();
this.firstSub.unsubscribe();
}

Angular Component: Impossible to loop through an array of object with TypeScypt

can any one please tell me why I can not loop through this array?
In ngOnInit, everything works fine. I got an array that I successfully display in the template.
But in ngAfterViewInit, console.log show the array but when looping through with "for of" or "forEach", nothing works.
import { JobsService } from '../jobs.service';
import {Job} from '../models/Job';
#Component({
selector: 'app-job',
templateUrl: 'job.component.html'
})
export class JobComponent implements OnInit, AfterViewInit {
title = 'Job';
jobs: Job[] = [];
InProcess = '';
CurrentPartner = '';
ShowProcess = false;
sended = '';
constructor(private jobsService: JobsService) {
}
ngOnInit() {
this.jobs = this.jobsService.getJobs();
}
ngAfterViewInit() {
console.log(this.jobs); // Show the array
// Nothing happened when looping through the array
this.jobs.forEach((oneJob) => {
console.log(oneJob);
});
}
}
Screenshot of the console in Google Chrome
The content of the service:
import { HttpClient, HttpErrorResponse } from '#angular/common/http';
import { Observable, throwError } from 'rxjs';
import { catchError } from 'rxjs/operators';
import {Job} from './models/Job';
interface IJob {
message: string;
jobs: any[];
}
#Injectable({
providedIn: 'root'
})
export class JobsService {
constructor(private httpClient: HttpClient) { }
private REST_API_SERVER = 'http://localhost:8080/myband/api/getjobs.php';
private REST_API_SERVER_SEND = 'http://localhost:8080/myband/api/sendjob.php';
jobList: Job[] = [];
errorMessage: any;
message: string;
static handleError(err: HttpErrorResponse) {
let errorMessage = '';
if (err.error instanceof ErrorEvent) {
errorMessage = `An error occurred: ${err.error.message}`;
} else {
errorMessage = `Server returned code: ${err.status}, error message is: ${err.message}`;
}
console.error(errorMessage);
return throwError(errorMessage);
}
public getJobs() {
this.requestJobs().subscribe(
iJob => {
this.message = iJob.message;
for (const job of iJob.jobs) {
const oneJob: Job = new Job(job);
this.jobList.push(oneJob);
}
},
error => this.errorMessage = error as any
);
return this.jobList;
}
public requestJobs(): Observable<IJob> {
return this.httpClient.get<IJob>(this.REST_API_SERVER).pipe(
catchError(JobsService.handleError)
);
}
}
The first thing I want to say to you is about isolation of responsibilities.
Your service must have just one job: provider one way to access your data; It means your logic inside getJobs() method could be done in your component.
export class JobsService {
constructor(
private httpClient: HttpClient,
) {}
private REST_API_SERVER = 'http://localhost:8080/myband/api/getjobs.php';
public requestJobs(): Observable<IJob> {
return this.httpClient.get<IJob>(this.REST_API_SERVER);
}
}
Now, you can handler your data in your component.
import { JobsService } from '../jobs.service';
#Component({
selector: 'app-job',
templateUrl: 'job.component.html'
})
export class JobComponent implements OnInit, AfterViewInit {
title = 'Job';
jobs$;
InProcess = '';
CurrentPartner = '';
ShowProcess = false;
sended = '';
constructor(private jobsService: JobsService) {
}
ngOnInit() {
this.jobs$ = this.jobsService.requestJobs();
}
ngAfterViewInit() {
this.jobs$
.pipe(
map(() => {}), // change your data here
catchError(() => {}) // handler your error here;
)
.subscribe(
() => {} // have access to your final data here.
);
}
}
Things to know:
You can remove the subscribe() execution and use the async pipe in your template;
The use of the operator map in pipe() is optional, you can handler your final data directly from your first callback subscribe().
You can convert your Observable to Promise using toPromise() method in one observable. Don't forgot async / await in your ngAfterViewInit.
Let me know if there is something I can help.
Try:
Object.keys(this.jobs).forEach(job => {
console.log(this.jobs[job]);
});
Try to assign an iterator function with below part replacement by this code:
// Nothing happened when looping through the array
this.jobs.forEach(oneJob, function(value, key) {
console.log(key + ': ' + value);
});
Usage of forEach in AngularJS:
For documentation try to check AngularJS forEach Docs
Syntax:
someIterable.forEach(object, iterator, [context])
Please check below example
class Job {
id: any;
status: any;
constructor(obj: any) {
this.id = obj.id;
this.status = obj.status;
}
}
let arr = [
{
id: 1,
status: "job"
}, {
id: 2,
status: "job2"
}
];
let newArr: any = [];
arr.forEach(a => {
let obj: Job = new Job(a);
newArr.push(obj);
})
console.log(newArr);
newArr.forEach((a: any) => {
console.log(a);
})

Can't use result from subscribe angular

I follow this guide, and i try to do something similar at Unrelated Components: Sharing Data with a Service paragraph
Data Service:
#Injectable()
export class MyDataService{
private messageSource = new BehaviorSubject(null);
currentMessage = this.messageSource.asObservable();
constructor(private http: HttpClient) {
setInterval(() => { this.changeMessage(this.resultFromRestCall()); }, 10 * 1000);
}
changeMessage(message: object) {
this.messageSource.next(message);
}
resultFromRestCall(){
const json;
this.http.get<object>(myApiUrl).subscribe(res =>
json['data'] = res['data'] //this is an example
);
return json;
}
Component:
export class MyComponent implements OnInit {
constructor(private dataservice: MyDataService) {}
ngOnInit() {
this.dataservice.currentMessage.subscribe(
message => {this.handleVarChange(message); }
);
}
handleVarChange(message) {
console.log(message.data);
}
With this code i got "undefined" in handleVarChange log
Instead of calling this.handleVarChange(message); in subscribe I write console.log(message) i got my result correctly.
So, my question is if it's possible use the value coming from data service in some function of my component.
Thanks in advance
With:
resultFromRestCall(){
const json;
this.http.get<object>(myApiUrl).subscribe(res =>
// takes x amount of time to populate json
json['data'] = res['data'] //this is an example
);
// executed instantly after above request has been called
return json;
}
You are returning json before it has been populated, since the request is asynchronous.
Instead you can flip it around a bit, and call resultFromRestCall() first, and when you get the response, then call changeMessage():
setInterval(() => {
this.resultFromRestCall().subscribe((data) => {
this.changeMessage(data);
});
}, 10 * 1000);
where resultFromRestCall simply returns an observable:
resultFromRestCall(){
return this.http.get<object>(myApiUrl);
}
Also remember to clearInterval in OnDestroy!
DEMO
Omit the .data in handleVarChange:
Instead of
handleVarChange(message) {
console.log(message.data);
}
write
handleVarChange(message) {
console.log(message);
}

need to know when answer received by function that listens to rxjs Observable

How do I use a method starting a listener on an observable which it returns in an if statement?
I'm in an Angular 5 project, I have this sort of setup in one of my components with an timeline where double click opens up a modal and you can type in the name for the item you're creating into that modal.
for the modals I used a reworked version of this answer. (I needed more up to date syntax and imports).
I've got it all nearly working now, here's my setup,
(timeline component which opens the modals) :
#Component({
selector: 'app-planning',
templateUrl: './planning.component.html',
styleUrls: ['./planning.component.css']
})
export class PlanningComponent implements AfterViewInit {
options = {
onAdd: (item, callback) => {
if(this.timeline.getCurrentTime() > item.start){
this.errorTimelineItemModal();
callback(null);
} else {
if (this.createNewTimelineItemModal()) { // <-- currently I have no return but
// having one would be meaningless
// anyways because the if wouldn't wait
// for the observable response and as a
// result, it would always assess false.
callback(item);
} else callback(null);
}
}
}
constructor(
private _element: ElementRef,
private modalService: BsModalService
) {}
ngAfterViewInit(){
this.container = this._element.nativeElement.querySelector('#timeline');
if (!this.items) {
this.items = new vis.DataSet(this.mydataset);
this.timeline = new vis.Timeline(this.container, this.items, this.groups, this.options);
}
}
createNewTimelineItemModal() {
const initialState = {
title: 'Ajouter',
multipleChoice: 'Bid',
choices: ['Bid', 'D.C.', 'Kickoff'],
accceptBtnName: 'Ajouter',
closeBtnName: 'Annuler',
};
this.bsModalRef = this.modalService.show(Modal, {initialState});
this.bsModalRef.content.onClose.subscribe(result => {
this.createItemResult = result;
console.log(JSON.stringify(result));
})
}
updateTimelineItemModal(name) {
const initialState = {
title: 'Nouveau Nom ?',
itemCurrentName: name,
accceptBtnName: 'Rennomer',
closeBtnName: 'Annuler',
};
this.bsModalRef = this.modalService.show(Modal, {initialState});
this.bsModalRef.content.onClose.subscribe(result => {
this.createItemResult = result;
console.log(JSON.stringify(result));
})
}
deleteTimelineItemModal() {
const initialState = {
title: 'Êtes-vous sûr de vouloir supprimer cet element?',
accceptBtnName: 'Supprimer',
closeBtnName: 'Annuler',
};
this.bsModalRef = this.modalService.show(Modal, {initialState});
this.bsModalRef.content.onClose.subscribe(result => {
this.createItemResult = result;
console.log(JSON.stringify(result));
})
}
errorTimelineItemModal() {
const initialState = {
title: 'Erreur',
list: ['Désolé, créer des éléments avant la date d\'aujourd\'hui est désactivé']
};
this.bsModalRef = this.modalService.show(Modal, {initialState});
this.bsModalRef.content.onClose.subscribe(result => {
this.createItemResult = result;
console.log(JSON.stringify(result));
})
}
}
(modal component) :
export class Modal implements OnInit {
onClose: Subject<Object>;
constructor(
private formBuilder: FormBuilder,
public _bsModalRef: BsModalRef) {}
ngOnInit(): void {
this.onClose = new Subject();
}
public onConfirm(): void {
this.onClose.next(true);
this._bsModalRef.hide();
}
public onCancel(): void {
this.onClose.next(false);
this._bsModalRef.hide();
}
}
As you can see I am getting an answer from validating or not the modal. I can console log it.
Now is where I'm stuck. How can I get the code execution to just halt until an observable has been received by that method so as to assess correctly within the if?
this is actually very important for the correct execution of my code because the callback(null); and callback(item); that you might have noticed are the syntaxe one must have to either finalize the item creation or prevent it.
see : http://visjs.org/docs/timeline/#Methods
I had this working with alerts but I'm trying to switch to something with more functionalities and cleaner.
If I can understand you correctly, you need to synchronize two separate events. It is usually a bad practice to do so.
Try to re-organise your code. It is an async process, so you should divide the process into sub-"transactions", that can happen separately.
Separate the logic for opening up your modal.
Wait for the user to enter the data
Process the answer from the modal.
Something like this:
createNewTimelineItemModal() {
const initialState = {
...
this.bsModalRef.content.onClose.subscribe(result => {
this.createItemResult = result;
this.continueToCreateItem(result);
});
}
private continueToCreateItem(result: any){
<insert your code here>
}
Or other solution can be to return observable objects and hande it within the onAdd
options = {
onAdd: (item, callback) => {
...
this.createNewTimelineItemModal().subscribe(result => {
if(result is something){
callback(item);
} else callback(null);
}
}
}
}
To "halt" the process is a pretty bad practice, but can be achived with Promise object.
this.myPromiseReturningMethod(params).then(() => {
but this will block all your application for the time being (with the user being unable to do anything) so I recommend to alter the structure instead.

What's an angular lifecycle-hook need when changing sets in componentInstance property by service?

I have a component that i send to MdDialog(Angular Material Dialog in my custom service.ts)
dialogRef = this.dialog.open(component, config);
And when I change a public property of this component by componentInstance like that:
dialogRef.componentInstance.task = task;
Angular shows me an error:
Error: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: 'undefined'. Current value: 'dialog'. It seems like the view has been created after its parent and its children have been dirty checked. Has it been created in a change detection hook ?
Full code of open-modal.service.ts
#Injectable()
export class TasksPopupService {
constructor(
private dialog: MdDialog,
private router: Router,
private tasksService: TasksService
) { }
public open(component: any, id?: string) {
if (id) {
this.tasksService.find(id)
.subscribe(task => {
this.bindDialog(component, task);
});
} else {
this.bindDialog(component, new Task());
}
}
bindDialog(component, task: Task) {
let dialogRef;
let config = new MdDialogConfig();
config.height = '80%';
config.width = '70%';
dialogRef = this.dialog.open(component, config);
dialogRef.componentInstance.task = task;
dialogRef.afterClosed().subscribe(res => {
this.router.navigate([{ outlets: { popup: null } }], { replaceUrl: true });
});
return dialogRef;
}
}
But an error occured only if id is undefined (in ELSE block) I think it's because of this.tasksService.find return Observable (async), and block ELSE is not async. But I'm not sure.
I has some confuse becouse error eccured in MdContainer of Angular Material.
If i get data from server it's need some time, but when i pass a new object it's occur fast and change detection is not finished if i understend right.
Also, it's not parent/child component and lifecycle hooks maybe not works as we expect.
I found solution, but it's not right. Just fast solution.
if (id) {
this.tasksService.find(id)
.subscribe(task => {
this.bindDialog(component, task);
});
} else {
Observable.of(new Task()).delay(300).subscribe(task => {
this.bindDialog(component, task);
});
}
I use delay for change detection has finished and error will not throw.

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