I am new to angular and I am trying to pass data from one component(HomeComponent) to another component(ProfileComponent) after navigation.
I created a shared service(DataService).
I injected the service in both the HomeComponent and ProfileComponent but when I set the value of the message property in HomeComponent and try to retrieve it in the ProfileComponent the value is undefined because the DataService is not the same instance.
The DataService was registered in the AppModule in the providers array so it should be a shared service and always the same instance right?
Thanks in advance
DataService.ts
import { Injectable } from '#angular/core';
#Injectable({
providedIn: 'root'
})
export class DataService {
message:string;
constructor() { }
}
HomeComponent.ts
import { Component, OnInit } from '#angular/core';
import { DataService } from '../services/data/data.service';
#Component({
selector: 'app-home',
templateUrl: './home.component.html',
styleUrls: ['./home.component.css']
})
export class HomeComponent implements OnInit {
constructor(private data:DataService) { }
ngOnInit() {
this.data.message = "hello world";
}
}
ProfileComponent.ts
import { Component, OnInit } from '#angular/core';
import { DataService } from '../services/data/data.service';
#Component({
selector: 'app-profile',
templateUrl: './profile.component.html',
styleUrls: ['./profile.component.css']
})
export class ProfileComponent implements OnInit {
private message : string;//undefined
constructor(private data:DataService) { }
ngOnInit() {
this.message = this.data.message;
}
}
AppModule.ts
import { BrowserModule } from '#angular/platform-browser';
import { NgModule } from '#angular/core';
import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { DataService } from './services/data/data.service';
import { HomeComponent } from './home/home.component';
import { ProfileComponent } from './profile/profile.component';
#NgModule({
declarations: [
AppComponent,
HomeComponent,
ProfileComponent
],
imports: [
BrowserModule,
AppRoutingModule
],
providers: [DataService],
bootstrap: [AppComponent]
})
export class AppModule { }
I know it's a 2 year question, but Google puts it at the top of search results
Now, Angular docs are clearer about this (or just we can find out easier), it's called "Singleton Services"
The section that explains this "bug" is The ForRoot Pattern and it says:
"If a module defines both providers and declarations (components, directives, pipes), then loading the module in multiple feature modules would duplicate the registration of the service. This could result in multiple service instances and the service would no longer behave as a singleton."
To sum up, if you define this in your services (DataService.ts) the providedIn: root as follows
#Injectable({ providedIn: 'root' })
you need to avoid define the service as a provider on your components or modules.
AppModule.ts
...
imports: [
BrowserModule,
AppRoutingModule
],
providers: [DataService], // This line is the problem
bootstrap: [AppComponent]
....
Hope that helps to somebody and if need more documentation refer to Singleton Services' link
Each time you inject the service to your component, new instance is generated. However in this case i would recommend you to use BehaviorSubject as follows,
#Injectable()
export class SharedService {
private messageSource = new BehaviorSubject<string>("default message");
currentMessage = this.messageSource.asObservable();
constructor() { }
changeMessage(message: string) {
this.messageSource.next(message)
}
STACKBLITZ DEMO
Related
I am using JSONPlaceholder to get data in service, but I am unable to get data at all. Please, help me out.
user.component.html
<p (click)="getUsers()">Click Me!</p>
<ul *ngFor="let x of users">
<li>{{x.name}}, {{x.age}}</li>
</ul>
user.component.ts
import { Component, OnInit } from '#angular/core';
import { Observable } from 'rxjs/Observable';
import { DataService } from '../../services/data.service';
import { Http } from '#angular/http';
#Component({
selector: 'app-user',
templateUrl: './user.component.html',
styleUrls: ['./user.component.css']
})
export class UserComponent implements OnInit {
constructor(private http:Http) { }
ngOnInit() {
}
getUsers(){
console.log(this.http.get("https://jsonplaceholder.typicode.com/posts"));
}
}
app.module.ts
//Basic File Inclusions
import { BrowserModule } from '#angular/platform-browser';
import { NgModule } from '#angular/core';
//Additional files inclusion
import { AppComponent } from './app.component';
import { UserComponent } from './components/user/user.component';
import { DataService } from './services/data.service';
import { Http } from '#angular/http';
#NgModule({
declarations: [
AppComponent,
UserComponent
],
imports: [
BrowserModule
],
providers: [ Http ],
bootstrap: [AppComponent]
})
export class AppModule { }
Please, can someone help me out making a successfull service call via http and get data on console.
Import
import { HttpModule } from '#angular/http';
in app.module.ts
imports: [HttpModule]
Rest of code will be same as you posted.
calling http like
this.http.get(`https://jsonplaceholder.typicode.com/posts`).subscribe(
data => {
console.log(data)
});
user.component.ts
import { Component, OnInit } from '#angular/core';
import { Observable } from 'rxjs/Observable';
import { DataService } from '../../services/data.service';
import { Http } from '#angular/http';
import { HttpClient } from '#angular/common/http';
#Component({
selector: 'app-user',
templateUrl: './user.component.html',
styleUrls: ['./user.component.css']
})
export class UserComponent implements OnInit {
constructor(private http: HttpClient) { }
ngOnInit() {
}
this.http.get(`https://jsonplaceholder.typicode.com/posts`).subscribe(
data => {
console.log(data)
});
}
app.module.ts
//Basic File Inclusions
import { BrowserModule } from '#angular/platform-browser';
import { NgModule } from '#angular/core';
//Additional files inclusion
import { AppComponent } from './app.component';
import { UserComponent } from './components/user/user.component';
import { DataService } from './services/data.service';
import { Http } from '#angular/http';
import { HttpModule } from "#angular/http";
#NgModule({
declarations: [
AppComponent,
UserComponent
],
imports: [
BrowserModule,
HttpModule
],
providers: [ Http ],
bootstrap: [AppComponent]
})
export class AppModule { }
Hope this may help you..
You are just calling http.get(url) and expecting something in return is like calling ajax method without success and error callback methods.
Kindly check Http documentation and usage of get and post methods
Mistake/Wrong Assumptions:
this.http.get(https://jsonplaceholder.typicode.com/posts) will not return http response which are expecting
Reality/Correct Approach:
You can use either pipe(can be used in the service) or subscribe(can be used in Component) method on http's get method whose return type is Observable.
Based on your requirement, you can use either of them
http.get('https://jsonplaceholder.typicode.com/posts')
// Call map on the response observable to get the parsed people object
.pipe(map(res => res.json()))
// Subscribe to the observable to get the parsed people object and attach it to the
// component
.subscribe(posts => this.posts = posts)
Hence your component code becomes:
user.component.ts
import { Component, OnInit } from '#angular/core';
import { Observable } from 'rxjs/Observable';
import { DataService } from '../../services/data.service';
import { Http } from '#angular/http';
#Component({
selector: 'app-user',
templateUrl: './user.component.html',
styleUrls: ['./user.component.css']
})
export class UserComponent implements OnInit {
constructor(private http:Http) { }
ngOnInit() {
}
getUsers(){
this.http.get("https://jsonplaceholder.typicode.com/posts")
.subscribe(posts=> console.log(posts))
}
}
Im having some trouble figuring this out, basically I have a headerTitleService which I want to be able to dynamically set the title in my header component but for some reason when I set the title nothing shows up? Im not getting any errors so I can seem to figure out what the problem is..
headerTitle.service.ts
import { Injectable } from '#angular/core';
import { BehaviorSubject } from 'rxjs/BehaviorSubject';
#Injectable()
export class HeaderTitleService {
title = new BehaviorSubject('');
constructor() { }
setTitle(title: string) {
this.title.next(title);
}
}
header.component.ts
import { Component, OnInit } from '#angular/core';
import { HeaderTitleService } from '../../../services/headerTitle.service'
#Component({
selector: 'app-header',
templateUrl: './header.component.html',
styleUrls: ['./header.component.scss'],
providers: [HeaderTitleService]
})
export class HeaderComponent implements OnInit {
title: string;
constructor(
private headerTitleService: HeaderTitleService
) { }
ngOnInit() {
this.headerTitleService.title.subscribe(updatedTitle => {
this.title = updatedTitle;
});
}
}
header.component.html
<h1>{{title}}</h1>
home.component.ts
import { Component, OnInit } from '#angular/core';
import { HeaderTitleService } from '../../services/headerTitle.service';
#Component({
selector: 'app-home',
templateUrl: './home.component.html',
styleUrls: ['./home.component.scss'],
providers: [HeaderTitleService]
})
export class HomeComponent implements OnInit {
constructor(
private headerTitleService: HeaderTitleService
) { }
ngOnInit() {
this.headerTitleService.setTitle('hello');
}
}
The line providers: [HeaderTitleService] in each component means that they will be given one HeaderTitleService each, rather than one between them.
To fix this remove providers: [HeaderTitleService] from your components, and place it in your module definition instead:
#NgModule({
providers: [HeaderTitleService]
})
Move HeaderTitleService in providers of your module. With your implementation you receive new instance of the HeaderTitleService in each component.
Hope this helps.
I am working on my first Angular app and dealing with the HttpClientModule in my component and getting errors.
following the docs Angular -HttpClient I installed the HttpClientModule in the app.module.ts as instructed, then in my emails.component.ts I have the following:
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-emails',
templateUrl: './emails.component.html',
styleUrls: ['./emails.component.scss'],
results: string[]
})
export class EmailsComponent implements OnInit {
constructor(private http: HttpClient) { }
ngOnInit() {
this.http.get('/api/email_list.json').subscribe(data => {
this.results = data['results'];
});
}
}
which is giving me the following error in my console:
ERROR in src/app/components/emails/emails.component.ts(7,3): error TS2345: Argument of type '{ selector: string; templateUrl: string; styleUrls: string[]; results: any; }' is not assignable to parameter of type 'Component'.
Object literal may only specify known properties, and 'results' does not exist in type 'Component'.
src/app/components/emails/emails.component.ts(7,12): error TS2693: 'string' only refers to a type, but is being used as a value here.
src/app/components/emails/emails.component.ts(7,19): error TS1109: Expression expected.
src/app/components/emails/emails.component.ts(12,29): error TS2304: Cannot find name 'HttpClient'.
src/app/components/emails/emails.component.ts(16,12): error TS2339: Property 'results' does not exist on type 'EmailsComponent'.
app.module.ts:
import { BrowserModule } from '#angular/platform-browser';
import { NgModule } from '#angular/core';
import { HttpClientModule } from '#angular/common/http';
import { AppComponent } from './app.component';
import { EmailsComponent } from './components/emails/emails.component';
#NgModule({
declarations: [
AppComponent,
EmailsComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }
you're component should be:
first you need to import HttpClient
second results: string[] should be inside the class not at decoration component exactly as I did here :
import { Component, OnInit } from '#angular/core';
import { HttpClient } from '#angular/common/http';
#Component({
selector: 'app-emails',
templateUrl: './emails.component.html',
styleUrls: ['./emails.component.scss']
})
export class EmailsComponent implements OnInit {
results: string[];
constructor(private http: HttpClient) { }
ngOnInit() {
this.http.get('/api/email_list.json').subscribe(data => {
this.results = data['results'];
});
}
}
Please read the description carefully, they explaining you need to load HttpClient.
In your app module you forgot to provide.
import { BrowserModule } from '#angular/platform-browser';
import { NgModule } from '#angular/core';
import { HttpClientModule } from '#angular/common/http';
import { AppComponent } from './app.component';
import { EmailsComponent } from './components/emails/emails.component';
#NgModule({
declarations: [
AppComponent,
EmailsComponent
],
imports: [
BrowserModule,
HttpClientModule
],
providers: [HttpClient],
bootstrap: [AppComponent]
})
export class AppModule { }
Then in your component:
import { Component, OnInit } from '#angular/core';
import { HttpClient } from '#angular/common/http';
#Component({
selector: 'app-emails',
templateUrl: './emails.component.html',
styleUrls: ['./emails.component.scss']
})
export class EmailsComponent implements OnInit {
results: string[]
constructor(private http: HttpClient) { }
ngOnInit() {
this.http.get('/api/email_list.json').subscribe(data => {
this.results = data['results'];
});
}
}
I have created two components and one shared service, i want pass data from one component to another, but i am getting empty object
bellow is 1st component
import { Component, OnInit } from '#angular/core';
import {SharedService} from './../shared.service';
import { Router, NavigationStart } from '#angular/router';
#Component({
selector: 'app-cone',
templateUrl: './cone.component.html',
styleUrls: ['./cone.component.css'],
providers: [SharedService]
})
export class ConeComponent implements OnInit {
req = <any>{};
constructor(public service:SharedService,private router:Router) { }
send(){
this.req.fname= "ketan";
this.req.lname= "pradhan";
this.service.saveData(this.req);
console.log('str');
this.router.navigate(['/apps/ctwo']);
}
ngOnInit() {
}
}
Bellow is the 2nd component where i need to pass the data from 1st comonent, i am getting empty object is this.myName
import { Component, OnInit } from '#angular/core';
import {SharedService} from './../shared.service';
import { Router, NavigationStart } from '#angular/router';
#Component({
selector: 'app-ctwo',
templateUrl: './ctwo.component.html',
styleUrls: ['./ctwo.component.css'],
providers: [SharedService]
})
export class CtwoComponent implements OnInit {
myName= <any>{};
constructor(public service:SharedService,private router:Router) {
this.myName=this.service.getData();
console.log(this.myName);
}
ngOnInit() {
}
}
Bellow is shared service which is for communicating between 2 components
import {Component, Injectable,Input,Output,EventEmitter} from '#angular/core'
// Name Service
export interface myData {
name:string,
lname:string
}
#Injectable()
export class SharedService {
sharingData: myData=<any>{};
saveData(str){
console.log('save data function called' + str.fname);
console.log(this.sharingData);
this.sharingData = str;
// this.sharingData.lname=str.lname;
console.log(this.sharingData)
}
getData()
{
console.log('get data function called');
return this.sharingData;
}
}
When you are setting providers arrays at component level, it means that you have two separate instances of the service in this case.
You need to declare the service in your NgModule providers array instead, then the two components (and any other components in that module) will have the same instance of the service.
So remove the providers arrays in your components, and instead add the service to providers array in your NgModule.
#Component({
selector: 'app-ctwo',
templateUrl: './ctwo.component.html',
styleUrls: ['./ctwo.component.css'],
// providers: [SharedService] // remove these!
})
and instead....
#NgModule({
imports: [ ... ],
declarations: [ .. ],
bootstrap: [ ... ],
providers: [ SharedService ] // here!
})
I am trying to create a reusable component that serves as a processing overlay when making asynchronous calls across my site. I have a service in place but the OverlayComponent doesn't seem to get invoked when showOverlay is invoked:
app.module.ts
import { NgModule } from '#angular/core';
import { BrowserModule } from '#angular/platform-browser';
import { HashLocationStrategy, LocationStrategy } from '#angular/common';
import { HttpModule } from '#angular/http';
import { AppRoutingModule } from './app-routing.module';
import { MainComponent } from './app.mysite.component';
import { OverlayComponent } from './app.mysite.overlay.component';
import { TrackerComponent } from './pages/tracker/mysite.tracker.component';
import { OverlayService } from "./overlay.service";
#NgModule({
imports: [ BrowserModule, AppRoutingModule, HttpModule ],
declarations: [
MainComponent,
OverlayComponent,
NavbarComponent,
TrackerComponent,
],
providers: [{provide: LocationStrategy, useClass: HashLocationStrategy}, OverlayService],
bootstrap: [ MainComponent ]
})
export class AppModule { }
TrackerComponent.ts
import { Component, OnInit } from '#angular/core';
import { OverlayService } from '../../overlay.service.js';
#Component({
moduleId: module.id,
selector: 'tracker-component',
templateUrl: '/public/app/templates/pages/tracker/mysite.tracker.component.html',
providers: [ OverlayService]
})
export class TrackerComponent implements OnInit{
constructor(private http: Http, private overlayService: OverlayService) {
}
ngOnInit(): void {
this.overlayService.showOverlay('Processing...'); //This kicks everything off but doesn't show the alert or overlay
this.overlayService.test(); //does exactly what i'd expect
}
}
overlay.service.ts
import { Injectable } from '#angular/core';
import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';
#Injectable()
export class OverlayService {
private message: string;
private subject: Subject<any> = new Subject<any>();
showOverlay(msg: string) : void { //When this gets invoked, shouldn't it be invoking a change to this.subject and therefore invoking getMessage()
this.message = msg;
this.subject.next(msg);
}
getMessage(): Observable<any> {
return this.subject.asObservable();
}
test() {
return 'test good'; //if I call this function, it works
}
}
app.mysite.overlay.component
import { Component, OnInit } from '#angular/core';
import { OverlayService } from './overlay.service';
#Component({
selector: 'overlay-component',
templateUrl: '/public/app/templates/mysite.overlay.component.html',
styleUrls: ['public/app/scss/overlay.css'],
providers: [OverlayService]
})
export class OverlayComponent implements OnInit {
private processingMessage: string;
constructor(private overlayService: OverlayService) {}
ngOnInit() {
this.overlayService.getMessage().subscribe((message: string) => { //since i'm subscribed to this, i'm expecting this to get called. It doesn't
this.processingMessage = message;
alert(this.processingMessage); //never gets hit
$('.overlay-component-container').show(); // never gets hit
},
error => {
alert('error');
})
}
}
Specifying providers in the Component metadata actually creates a new injectable, scoped to that component tree.
If you want to share the overlay service across the app, you'll need to declare the overlay provider in the NgModule, and not in the components. Alternatively, you can declare it only as a provider on the top-level entry component (eg. AppComponent), though it may cause confusion when used in other entry components/lazy-loaded modules.
See https://angular.io/docs/ts/latest/guide/hierarchical-dependency-injection.html for a better explanation