here is my angular component -
export class UserListComponent implements OnInit, OnDestroy {
private _subscriptions: Subscription;
private _users: User[] = [];
private _clickableUser: boolean = true;
constructor(
private route: ActivatedRoute,
) { }
ngOnInit() {
const source = interval(1000);
const users = this.route.snapshot.data['users'] as IUserInterface[];
this._subscriptions = source.subscribe(() => this._users = users.map(user => new User(user)))
}
ngOnDestroy() {
this._subscriptions.unsubscribe();
}
i get the data, but the interval does not set it without refreshing.
ngOnInit() is only called once, when a component is first created. This means that your active route is being read only once, which also means that your users array is always the same one.
I'm guessing you are trying to update your component each time the route data gets updated. For that, you need to subscribe to this.route.data (notice I didn't include snapshot). It will look something like this:
this._subscriptions = this.route.data.subscribe(data => this._users = data['users'].map(user => new User(user));
Related
I'm trying to find a way to share a variable between my components in Angular. My variable that I pass to my child components are interchangeable between their child components. I used service for this, but still could not solve the problem. I am sharing a demo by simplifying my operations using BehaviorSubject.
demo : https://stackblitz.com/edit/angular-ivy-6usdww?file=src%2Fapp%2Fhello.component.ts
My problem is:
i am sending variables from my app.component.ts component to hello and hello-a components. i am mutating variable in hello component. However, just before that I point the first version to a service. however, the changed status is forwarded.
hello.component
export class HelloComponent {
#Input() colDef: any[];
col: any[];
constructor(private columnDefService: ColumnDefService) {}
ngOnInit() {
let colDefFirst = Object.assign([], this.colDef);
this.columnDefService.setFirstColDef(colDefFirst);
this.setColumnDef(this.colDef);
}
setColumnDef(colDef: any[]): void {
let rC: any = Object.assign([], colDef);
rC[0].hide = true;
this.columnDefService.setColDef([].concat(rC));
this.columnDefService.colDef$.subscribe((colDef: any) => {
this.col = colDef;
});
}
}
hello-a.component
export class HelloAComponent {
#Input() colDef: any[];
firstColDef: any[] = [];
constructor(private ColumnDefService: ColumnDefService) {}
ngOnInit() {
this.ColumnDefService.firstColDef$.subscribe((firstColDef: any) => {
console.log('firstColDef', firstColDef);
this.firstColDef = firstColDef;
});
}
}
coldef.service
#Injectable({
providedIn: 'root'
})
export class ColumnDefService {
private colDefSource = new BehaviorSubject([]);
private firstColDefSource = new BehaviorSubject([]);
colDef$ = this.colDefSource.asObservable();
firstColDef$ = this.firstColDefSource.asObservable();
setColDef(colDef: any) {
this.colDefSource.next(colDef);
}
setFirstColDef(colDef: any) {
this.firstColDefSource.next(colDef);
}
}
this is what i want to do:
storing my variable in a component for future use. i want to continuously change my variable on demand in my other component.
thanks for your advice
So I asked a question a few days ago and got some headway on a solution, however now I'm stuck at another wall I'm unsure how to get over.
I have two parent components, a shared view/component with an extended base component, and a service all hooked together. The objective is to use the two parent components to drive what data is shown within the shared component. The two parent components use references to service methods passed into the shared component to get the data.
I've reached an issue where my http.get is always undefined no matter what I try. I've instantiated it like I do in my other services but I've had no luck. I suspect this is caused by how i pass in my service references. Code below:
Parent Component Code:
// PARENT COMPONENT
myData$: Observable<myType>;
searchMethod: Function;
constructor(private myService){
this.myData$ = this.myService.myData$;
this.searchMethod = this.myService.searchData;
}
// PARENT COMPONENT HTML
<app-shared-component
[myData$] = "myData$"
[searchMethod]="searchMethod">
</app-shared-component>
Shared Component Code:
export class MySharedComponent extends BaseComponent<MyType> implements OnInit {
#Input() myData$: Observable<myType>;
#Input() searchMethod: Function;
constructor() { super(); }
ngOnInit(): void {
this.data$ = this.myData$;
}
search(): void {
this.searchMethod().subscribe(//do something);
}
Base Component Code:
#Input data$: Observable<T>;
ngOnInit(): void {
this.data$.subscribe((response: T) => //do something);
super.ngOnInit();
}
Service Code:
private myDataSubject = new BehaviorSubject<MyType>(new MyType());
get myData$(): Observable<MyType> {
return this.myDataSubject.asObservable();
}
constructor(private http: HttpClient) { }
searchData(): Observable<void> {
return new Observable<void>(observer => {
this.http.get<MyType>(
'http://myuri'
).subscribe(
response => {
// do something
},
() => observer.error(),
() => observer.complete()
);
});
}
It looks like you're losing the context of your service when you set this.searchMethod = this.myService.searchData in your parent component. It should work if you change searchData() { to an arrow function: searchData = (): Observable<void> => {.
I have an Ionic application where I have created a component to show some data of an object. My problem is that when I update the data in the parent that hosts the component the data within the component does not update:
my-card.component.ts
#Component({
selector: 'my-card',
templateUrl: './my-card.html'
})
export class MyCard {
#Input('item') public item: any;
#Output() itemChange = new EventEmitter();
constructor() {
}
ngOnInit() {
// I do an ajax call here and populate more fields in the item.
this.getMoreData().subscribe(data => {
if (data.item){
this.item = data.item;
}
this.itemChange.emit(this.item);
});
}
}
my-card.html
<div class="comment-wrapper" *ngFor="let subitem of item.subitems">
{{subitem.title}}
</div>
And in the parent I use the component like this:
<my-card [(item)]="item"></my-card>
And the ts file for the parent:
#IonicPage()
#Component({
selector: 'page-one',
templateUrl: 'one.html',
})
export class OnePage {
public item = null;
constructor(public navCtrl: NavController, public navParams: NavParams) {
this.item = {id:1, subitems:[]};
}
addSubItem():void{
// AJAX call to save the new item to DB and return the new subitem.
this.addNewSubItem().subscribe(data => {
let newSubItem = data.item;
this.item.subitems.push(newSubItem);
}
}
}
So when I call the addSubItem() function it doesnt update the component and the ngFor loop still doesnt display anything.
You are breaking the object reference when you are making the api request. You are assigning new value, that is overwriting the input value you get from the parent, and the objects are no longer pointing to the same object, but item in your child is a completely different object. As you want two-way-binding, we can make use of Output:
Child:
import { EventEmitter, Output } from '#angular/core';
// ..
#Input() item: any;
#Output() itemChange = new EventEmitter();
ngOnInit() {
// I do an ajax call here and populate more fields in the item.
this.getMoreData(item.id).subscribe(data => {
this.item = data;
// 'recreate' the object reference
this.itemChange.emit(this.item)
});
}
Now we have the same object reference again and whatever you do in parent, will reflect in child.
If the getMoreData method returns an observable, this code needs to look as follows:
ngOnInit() {
// I do an ajax call here and populate more fields in the item.
this.getMoreData().subscribe(
updatedItem => this.item = updatedItem
);
}
The subscribe causes the async operation to execute and returns an observable. When the data comes back from the async operation, it executes the provided callback function and assigns the item to the returned item.
You declared item with #Input() decorator as:
#Input('item') public item: any;
But you use two-way binding on it:
<my-card [(item)]="item"></my-card>
If it is input only, it should be
<my-card [item]="item"></my-card>
Now if you invoke addSubItem() it should display the new added item.
this.item = this.getMoreData();
The getMoreData() doesn't make sense if you put it in your card component as you want to use the item passed via #Input()
Your component interactions are a little off. Check out the guide on the Angular docs (https://angular.io/guide/component-interaction). Specifically, using ngOnChanges (https://angular.io/guide/component-interaction#intercept-input-property-changes-with-ngonchanges) or use a service to subscribe and monitor changes between the parent and the child (https://angular.io/guide/component-interaction#parent-and-children-communicate-via-a-service).
Im learning Angular 4 and have run into a problem that I cannot seem to find a solution to. Here is the context:
I have a simple app that displays info about US Presidents.
The backend is a rest API provided by webapi...this works fine.
The front end is an Angular app.
Ive distilled the problem down to 3 components, 1 data service and 1 model.
Here is the model:
export class President {
constructor(
public id: number,
public presidentName: string,
public presidentNumber: number,
public yearsServed: string,
public partyAffiliation: string,
public spouse: string) {}
}
The 3 components are
1. SearchComponent
2. HomeComponent
3. PresidentComponent
When the app bootstraps, it loads the ApplicationComponent - it is the root component:
import { Component, ViewEncapsulation } from '#angular/core';
#Component({
selector: 'my-app',
template: `
<search-component></search-component>
<home-component></home-component>
`
})
export class ApplicationComponent {}
PresidentComponent is a child component of HomeComponent. When home component loads, it makes an http call to the api to get a list of presidents and renders 1 presidentComponent for each row returned. This works fine.
What Im trying to do is implement a search feature where the dataService exposes an EventEmitter and provides the search method as shown here:
import { Injectable, EventEmitter, Output } from '#angular/core'
import { President } from '../models/President'
import { Http } from '#angular/http';
import 'rxjs/add/operator/toPromise';
import 'rxjs/add/operator/map';
import { Observable } from 'rxjs/Observable';
#Injectable()
export class DataService {
constructor(private http: Http) {
}
searchEvent: EventEmitter<any> = new EventEmitter();
// simple property for the url to the api
get presidentUrl {
return "http://localhost:51330/api/presidents";
}
search(params: any): Observable<President[]> {
let encParams = encodeParams(params);
console.log(encParams);
return this.http
.get(this.presidentUrl, {search: encParams})
.map(response => response.json());
}
getParties(): String[] {
return ['Republican', 'Democrat', 'Federalist', 'Whig', 'Democratic-Republican', 'None'];
}
getPresidents(): Observable<President[]> {
return this.http.get(this.presidentUrl)
.map(response => response.json());
}
}
/**
* Encodes the object into a valid query string.
* this function is from the book Angular2 Development with TypeScript
*/
function encodeParams(params: any): URLSearchParams {
return Object.keys(params)
.filter(key => params[key])
.reduce((accum: URLSearchParams, key: string) => {
accum.append(key, params[key]);
return accum;
}, new URLSearchParams());
}
The Search Component houses the search form and when the search button is clicked, it executes the onSearch() function and calls emit on the data service:
onSearch(){
if(this.formModel.valid){
console.log('emitting event from search.ts');
this.dataService.searchEvent.emit(this.formModel.value);
}
}
Then, in the HomeComponent, I want to subscribe to this event and execute a search via the dataservice when it fires:
ngOnInit(): void {
//when component loads, get list of presidents
this.dataService.getPresidents()
.subscribe(
presidents => {
console.log('sub');
this.presidents = presidents;
},
error => console.error(error)
)
//when search event is fired, do a search
this.dataService.searchEvent
.subscribe(
params => {
console.log('in home.ts subscribe ' + JSON.stringify(params));
this.result = this.dataService.search(params);
},
err => console.log("cant get presidents. error code: %s, URL: %s"),
() => console.log('done')
);
}
When I run this in the browser, everything works except the http call is never executed. If I subscribe() to the http.get call in the dataservice itself, it executes but why should I have to do that when I have a subscription being setup on the HomeComponent?
I want to handle the Observable in the HomeComponent and update the list of presidents that is being displayed in the UI based on the search result.
Any advice is greatly appreciated.
The entire idea of using EventEmitter in the service is not right. The EventEmitter should be used with #Output properties to send data from the child component to its parent.
Even though the EventEmitter is a subclass of the Subject, you shouldn't be using it in services. So inject the service into your component, subscribe to its observable in the component, and emit an event using EventEmitter to the parent component if need be.
In the code this.result = this.dataService.search(params);, result is an observable. You have not made a subscription.
In that case you should have used the async pipe to display the data.
Why not use Subject from rxjs. Here is what i am proposing:
DataService:
import { Observable, Subject } from "rxjs";
import 'rxjs/add/operator/catch';
#Injectable()
export class DataService {
private _dataSubject = new Subject();
constructor(private http: Http) {
this.http.get(this.presidentUrl)
.map(response => this._dataSubject.next(response.json()))
.catch(err => this._dataSubject.error(err));
);
}
// simple property for the url to the api
get presidentUrl {
return "http://localhost:51330/api/presidents";
}
search(params: any){
let encParams = encodeParams(params);
console.log(encParams);
this.http
.get(this.presidentUrl, {search: encParams})
.map(response => this._dataSubject.next(response.json()))
.catch(err => this._dataSubject.error(err));
}
getParties(): String[] {
return ['Republican', 'Democrat', 'Federalist', 'Whig', 'Democratic-Republican', 'None'];
}
getPresidents(): Observable<President[]> {
return this._dataSubject;
}
SearchComponent:
onSearch(){
if(this.formModel.valid){
console.log('emitting event from search.ts');
this.dataService.search(this.formModel.value);
}
}
With these modifications you should be able to have only 1 subscriber in homeCompoent and then get new data emitted every time onSearch() is called.
I have a component which receives an array of image objects as Input data.
export class ImageGalleryComponent {
#Input() images: Image[];
selectedImage: Image;
}
I would like when the component loads the selectedImage value be set to the first object of the images array. I have tried to do this in the OnInit lifecycle hook like this:
export class ImageGalleryComponent implements OnInit {
#Input() images: Image[];
selectedImage: Image;
ngOnInit() {
this.selectedImage = this.images[0];
}
}
this gives me an error Cannot read property '0' of undefined which means the images value isn't set on this stage. I have also tried the OnChanges hook but I'm stuck because i can't get information on how to observe changes of an array. How can I achieve the expected result?
The parent component looks like this:
#Component({
selector: 'profile-detail',
templateUrl: '...',
styleUrls: [...],
directives: [ImageGalleryComponent]
})
export class ProfileDetailComponent implements OnInit {
profile: Profile;
errorMessage: string;
images: Image[];
constructor(private profileService: ProfileService, private routeParams: RouteParams){}
ngOnInit() {
this.getProfile();
}
getProfile() {
let profileId = this.routeParams.get('id');
this.profileService.getProfile(profileId).subscribe(
profile => {
this.profile = profile;
this.images = profile.images;
for (var album of profile.albums) {
this.images = this.images.concat(album.images);
}
}, error => this.errorMessage = <any>error
);
}
}
The parent component's template has this
...
<image-gallery [images]="images"></image-gallery>
...
Input properties are populated before ngOnInit() is called. However, this assumes the parent property that feeds the input property is already populated when the child component is created.
In your scenario, this is not the case – the images data is being populated asynchronously from a service (hence an http request). Therefore, the input property will not be populated when ngOnInit() is called.
To solve your problem, when the data is returned from the server, assign a new array to the parent property. Implement ngOnChanges() in the child. ngOnChanges() will be called when Angular change detection propagates the new array value down to the child.
You can also add a setter for your images which will be called whenever the value changes and you can set your default selected image in the setter itself:
export class ImageGalleryComponent {
private _images: Image[];
#Input()
set images(value: Image[]) {
if (value) { //null check
this._images = value;
this.selectedImage = value[0]; //setting default selected image
}
}
get images(): Image[] {
return this._images;
}
selectedImage: Image;
}
You can resolve it by simply changing few things.
export class ImageGalleryComponent implements OnInit {
#Input() images: Image[];
selectedImage: Image;
ngOnChanges() {
if(this.images) {
this.selectedImage = this.images[0];
}
}
}
And as another one solution, you can simply *ngIf all template content until you get what you need from network:
...
<image-gallery *ngIf="imagesLoaded" [images]="images"></image-gallery>
...
And switch flag value in your fetching method:
getProfile() {
let profileId = this.routeParams.get('id');
this.profileService.getProfile(profileId).subscribe(
profile => {
this.profile = profile;
this.images = profile.images;
for (var album of profile.albums) {
this.images = this.images.concat(album.images);
}
this.imagesLoaded = true; /* <--- HERE*/
}, error => this.errorMessage = <any>error
);
}
In this way you will renderout child component only when parent will have all what child needs in static content. It's even more useful when you have some loaders/spinners that represent data fetching state:
...
<image-gallery *ngIf="imagesLoaded" [images]="images"></image-gallery>
<loader-spinner-whatever *ngIf="!imagesLoaded" [images]="images"></loader-spinner-whatever>
...
But short answer to your questions:
When inputs are available?
In OnInit hook
Why are not available to your child component?
They are, but at this particular point in time they were not loaded
What can I do with this?
Patiently wait to render child component utul you get data in asynchronous manner OR learn child component to deal with undefined input state