Develop Reference

displaying items from DB using Angular 12

the Item file
component file
the data service file
when I test my code with console log statements it says data from service is undefined
import { Component, OnInit } from '#angular/core';
import { Item } from '../item';
import { DataService } from '../data.service';
#Component({
selector: 'app-shopping-item',
templateUrl: './shopping-item.component.html',
styleUrls: ['./shopping-item.component.css'],
providers: [DataService]
})
export class ShoppingItemComponent implements OnInit {
shoppingItemList: Item[] = [];
constructor(private dataservice: DataService){}
getItems(){
this.dataservice.getShoppingItems()
.subscribe(items =>{
this.shoppingItemList.push(items),
console.log('data from dataservice '+ this.shoppingItemList[0].itemName);
})
}
addItem(form: any){
console.log(form)
}
ngOnInit(): void {
this.getItems();
}
}

If you are receiving an array from the API call, then you need to either assign it directly to the property (1) or destructure the array into the property (2)
Currently I guess you are pushing an array inside an array, which might lead to undefined error!
import { Component, OnInit } from '#angular/core';
import { Item } from '../item';
import { DataService } from '../data.service';
#Component({
selector: 'app-shopping-item',
templateUrl: './shopping-item.component.html',
styleUrls: ['./shopping-item.component.css'],
providers: [DataService]
})
export class ShoppingItemComponent implements OnInit {
shoppingItemList: Item[] = [];
constructor(private dataservice: DataService){}
getItems(){
this.dataservice.getShoppingItems()
.subscribe(items =>{
this.shoppingItemList = items; // solution 1
// this.shoppingItemList.push(...items); // solution 2
console.log('data from dataservice '+ this.shoppingItemList[0].itemName);
})
}
addItem(form: any){
console.log(form)
}
ngOnInit(): void {
this.getItems();
}
}

Angular does not rerender on Input() change

Whatever i do angular does not detect change on talks array. I have a handleSubmit function to send the toolbar. Toolbar use it to send the changes to parent from input field.
My app.component.ts file
import { Component, Type, OnChanges, SimpleChanges } from '#angular/core';
import { getResponse } from '../api/API';
declare module '../api/API' {
export interface NlpAPI {
getResponse(data: any): Promise<any>;
}
}
#Component({
selector: 'app-root',
templateUrl: './app.component.html',
styleUrls: ['./app.component.css'],
})
export class AppComponent implements OnChanges {
talks: string[];
title: string;
ngOnChanges(changes: SimpleChanges): void {
console.log(changes);
}
constructor() {
this.talks = [];
this.title = 'Talks';
}
ngOnInit() {
this.talks.push('Welcome to ProjectX! How can I help you?');
this.talks.push('I am a chatbot. I can help you with your queries.');
}
handleSubmit(data: any): void {
this.talks.push(data.talk);
}
messageResponse() {
// #ts-ignore: Object is possibly 'null'.
const x = document.getElementById('txt').value;
// #ts-ignore: Object is possibly 'null'.
document.getElementById('output').innerHTML =
'Your message is ' + '"' + x + '"';
}
}
My app.component.html
<!-- Toolbar -->
<app-custom-toolbar [handleSubmit]="handleSubmit"></app-custom-toolbar>
<!-- Highlight Card -->
<app-text-area [talksFromUser]="talks" [title]="title"></app-text-area>
<!-- Bottombar -->
<router-outlet></router-outlet>
My text-area.component.ts file
import { Component, Input, OnChanges, SimpleChanges } from '#angular/core';
#Component({
selector: 'app-text-area',
templateUrl: './text-area.component.html',
styleUrls: ['./text-area.component.css'],
})
export class TextAreaComponent implements OnChanges {
#Input() talksFromUser: string[] = [];
#Input() title: string = '';
constructor() {}
ngOnChanges(changes: SimpleChanges): void {
console.log(changes);
}
}
My text-area.component.html
<div class="main-text-area">
<div *ngFor="let item of talksFromUser">{{ item }}</div>
</div>
custom-toolbar.component.ts file
import { Component, Input, OnInit } from '#angular/core';
import { NgForm } from '#angular/forms';
#Component({
selector: 'app-custom-toolbar',
templateUrl: './custom-toolbar.component.html',
styleUrls: ['./custom-toolbar.component.css'],
})
export class CustomToolbarComponent implements OnInit {
talks: string[] = [];
#Input() handleSubmit!: (args: any) => void;
constructor() {}
ngOnInit(): void {}
onSubmit(f: NgForm) {
this.handleSubmit(f.value);
f.resetForm();
}
}
I tried also
this.talks = [...this.talks, data.talk]
Thank you all.

There are two issues in your code:
First one, you are calling handleSubmit("string") (so data is a string), but you are pushing data.talk, which is undefined (so talks will be [undefined, undefined, ...]). To fix it, use data:
handleSubmit(data: any): void {
this.talks.push(data); // use "data" instead of "data.talk"
}
Second one, you are using a AppComponent method into CustomToolbarComponent class. You need to keep the this scope of AppComponent. Also, you should use arrow functions:
handleSubmit = (data: any): void => {
this.talks.push(data);
}

Trigger cloned component when click on original in Angular

I have a loop on a component which represents a list of graph cards on my real app.
I have copied this component ( and loop it ) as the original
Hello Component
export class HelloComponent {
message:string;
printedMessage:string
#Input() elm:string;
constructor(private data: DataService, private router : Router) { }
ngOnInit() {
this.message = this.data.messageSource.value;
this.data.messageSource.subscribe(message => this.message = message)
}
updateService(){
this.data.changeMessage(this.message);
this.printedMessage=this.data.messageSource.value
}
navigateToSibling(){
this.router.navigate(['/sibling']);
}
}
app component
<div *ngFor="let elm of [1,2,3,4]">
<hello [elm]= "elm"></hello>
</div>
<h1>Copy </h1>
<div *ngFor="let elm of [1,2,3,4]">
<hello [elm]= "elm"></hello>
</div>
DataService component
export class DataService {
messageSource = new BehaviorSubject<string>("default message");
constructor() { }
changeMessage(message: string) {
this.messageSource.next(message)
}
}
Expected behaviour
What I would is when change the input value on the component 1 for example , only the value on the input of the copied component 1 changes.
Actual behaviour
Actually when I change a value inside an input all the other inputs are changings.
Here's a stackblitz example

Below is a solution that will solve you issue. This may not be a perfect solution but you need something similar.
hello.html
<h1>App component {{elm}}</h1>
<input type="text" [(ngModel)]="message">
<button (click)="updateService()" type="button">Save</button> {{printedMessage}}
Data Service
import {
Injectable
} from '#angular/core';
import {
BehaviorSubject
} from 'rxjs/BehaviorSubject';
#Injectable()
export class DataService {
messageSource = new BehaviorSubject < any > ("default message");
constructor() {}
changeMessage(message: string, elem: any) {
this.messageSource.next({
message: message,
elem: elem
});
}
}
HelloComponent
import {
Component,
Input
} from '#angular/core';
import {
DataService
} from "./dataService";
import {
Router
} from '#angular/router';
#Component({
selector: 'hello',
templateUrl: './hello.html',
styles: [`h1 { font-family: Lato; }`]
})
export class HelloComponent {
message: string;
printedMessage: string
#Input() elm: string;
constructor(private data: DataService, private router: Router) {}
ngOnInit() {
this.message = this.data.messageSource.value;
this.data.messageSource.subscribe(message => this.message = message.elem === this.elm ? message.message : this.message);
}
updateService() {
debugger
this.data.changeMessage(this.message, this.elm);
this.printedMessage = this.data.messageSource.value.message;
}
navigateToSibling() {
this.router.navigate(['/sibling']);
}
}
Have also updated the Stackblitz Demo. Hope this helps :)

Angular - communication from child-component to parent

I don't get i, how to communicate between components and services.. :(
I have read and tried a lot about even if some examples somehow work, I do not understand why (?)
what I want to achieve:
I have one parent and two child-components:
dashboard
toolbar
graph
in the toolbar-component I have a searchfield, which gets it's result from a external source (works via service).. when the result arrives, I need to trigger the updateGraph()-Method in the graph-component
toolbar.component.ts
import { Component, OnInit, Output, EventEmitter } from '#angular/core';
import { FormControl } from '#angular/forms';
import { WebsocketsService } from '../../../services/websockets/websockets.service';
import { DataService } from '../../../services/data/data.service';
#Component({
selector: 'toolbar',
templateUrl: './toolbar.component.html',
styleUrls: ['./toolbar.component.scss'],
providers: [WebsocketsService, DataService]
})
export class ToolbarComponent implements OnInit {
#Output() newGraphData: EventEmitter<boolean> = new EventEmitter();
searchField: FormControl;
search: string;
private isNewGraph = false;
constructor(private _websocketsService: WebsocketsService, private _dataService: DataService) {
}
ngOnInit() {
this.searchField = new FormControl();
this.searchField.valueChanges
.subscribe(term => {
this.search = term;
});
}
private applySearch() {
const res = this._websocketsService.sendQuery(this.search);
this._dataService.setGraphData(res);
this.newGraphData.emit(true);
this.search = '';
this.searchField.reset();
}
}
graph-component.ts
import { Component, OnInit} from '#angular/core';
import { HttpService } from '../../../services/http/http.service';
import { DataService } from '../../../services/data/data.service';
#Component({
selector: 'graph',
templateUrl: './graph.component.html',
styleUrls: ['./graph.component.scss'],
providers: [HttpService, DataService]
})
export class GraphComponent implements OnInit, AfterViewInit {
constructor( private _httpService: HttpService, private _dataService: DataService ) {
}
ngOnInit() {
}
public renderResult() {
console.log( this._dataService.getGraphData() );
}
}
data.service.ts
import { Injectable } from '#angular/core';
import { Subject } from 'rxjs/Subject';
#Injectable()
export class DataService {
private graphData: Subject<string> = new Subject<string>();
public setGraphData(data) {
this.graphData.next( data );
}
public getGraphData() {
return this.graphData;
}
constructor() { }
}
I simply want ´renderResult()´to be executed after the searchresult has been written to ´graphData´. please help i am confused.

If I understand, you want communication between components and service.
A[component] (make a information) -----(notification)-----> B[service] ----(send)----> C[component] (consume the information)
It's correct? Let's go.
You need create a subscription of graphData(data.service.ts) in GraphComponent.
import { Subscription } from 'rxjs/Subscription';
export class GraphComponent implements OnInit, AfterViewInit {
constructor( private _httpService: HttpService, private _dataService: DataService ) {
}
private subscription: Subscription;
ngOnInit() {
this.subscription = this._dataService.getGraphData().asObservable().subscribe((data) => {
console.log(data);
});
}
}
Look here to help you.
http://jasonwatmore.com/post/2016/12/01/angular-2-communicating-between-components-with-observable-subject

Short answer, I think you need to subscribe to the getGraphData subject, something like this (NOT RECOMMENDED):
public renderResult() {
this._dataService.getGraphData().subscribe(d => {
console.log(d)
});
}
It is not recommended as per the lead of RxJS says: https://medium.com/#benlesh/on-the-subject-of-subjects-in-rxjs-2b08b7198b93
Better answer, create an observable in your service and subscribe to that instead.
data.service.ts
graphObservable = this.graphData.asObservable();
graph-component.ts
public renderResult() {
this._dataService.graphObservable().subscribe(d => {
console.log(d)
});
}

How can I pass a variable from #Input to a service in an Angular2 component>

So, What I am trying to do seems like it would be trivial. And it probably is. But I can't figure it out. My question is:How can I pass a variable from #Input to a service in an Angular2 component? (Code has been simplified)
My component is as follows:
import { Component, Input } from '#angular/core';
import { CMSService } from '../cms.service';
#Component({
selector: 'cmstext',
templateUrl: './cmstext.component.html',
styleUrls: ['./cmstext.component.css']
})
export class CMSTextComponent {
constructor(private cms: CMSService) { }
#Input() id : string;
content = this.cms.getContent(this.id); // this.id is NULL so content is NULL
}
And then my service:
import { Injectable } from '#angular/core';
#Injectable()
export class CMSService {
constructor() { }
getContent(textId:string) : string {
this.text = textId; // textId is NULL so this.text returns NULL
return this.text;
}
}
My component template:
<p>id: {{id}}</p>
<p>Content: {{content}}</p>
When <cmstext id="4"></cmstext> is added to another component template the output is:
id: 4
content:
I'm just diving into Angular2 any help or suggestions would be greatly appreciated!

Just make it a setter and put the code there:
#Input()
set id(value : string) {
this.content = this.cms.getContent(value);
}

As pointed out by #Kris Hollenbeck,ngOnInit() was the answer. My final code looked like this. The component now passed the variable to the service.
import { Component, Input, OnInit } from '#angular/core';
import { CMSService } from '../cms.service';
#Component({
selector: 'cmstext',
templateUrl: './cmstext.component.html',
styleUrls: ['./cmstext.component.css']
})
export class CMSTextComponent implements OnInit {
public content : string;
#Input() id : string;
constructor(private cms: CMSService) { }
ngOnInit() {
this.content = this.cms.getContent(this.id);
}
}
This assigned the data from the service to the variable "content" and the id passed from the element attribute to the variable "id". Both variables were then accessible to the template!