How to transfer variables from a ts fie to another, angular - javascript

I defined a property here in my function
evs: string
...
openArticle(url){
this.evs = url
console.log(this.evs)
this.navCtrl.navigateForward('/url-page')
}
And I a trying to pass the value of 'this.evs' to another ts file and use its value but I do not know how to do this. I tried exporting it like this.
export const webpage = this.evs
but this.evs has no value until someone performs the openArticle function ad so I keep getting the error. "Cannot read property 'evs' of undefined"
What i need to do is tranfer the variable to the 'url-page' page and use the value of this.evs only after the openArticle function has bee called. How do I go about this?

As per my understanding you are trying to share data between two components.
So choose one of them as per your requirements.
Parent to Child: Sharing Data via Input().
Child to Parent: Sharing Data via Output() and EventEmitter.
Unrelated Components: Sharing Data with a Service.
This link will be helpful.

If the components have a parent/child relationship, You can share data between them via #Inpput() and #Output() decorators.
Sharing data from Parent to Child using #Input() :
<h3>Parent Component</h3>
<label>Parent Component</label>c
<input type="number" [(ngModel)]='parentValue'/>
<p>Value of child component is: </p>
<app-child [value]='parentValue'></app-child>
And in the child component, the 'parentValue' can be received as :
import { Component, OnInit, Input } from '#angular/core';
#Component({
selector: 'app-child',
templateUrl: './child.component.html',
styleUrls: ['./child.component.css']
})
export class ChildComponent implements OnInit {
#Input() value: number;
constructor() { }
ngOnInit() {
}
}
Now, in the case of sending data from Child to Parent, we can use an #Output() event emitter. So the parent would have a function to receive the emitted data from child as :
parent-app.component.html
<app-child [value]="parentValue" (childEvent)="childEvent($event)"></app-child>
parent-app.component.ts
childEvent(event) {
console.log(event);
}
And, the child.component.ts would look like :
import { Component, OnInit, Input, Output, EventEmitter } from '#angular/core';
#Component({
selector: 'app-child',
templateUrl: './child.component.html',
styleUrls: ['./child.component.css']
})
export class ChildComponent implements OnInit {
#Input() PData: number;
#Output() childEvent = new EventEmitter();
constructor() { }
onChange(value) {
this.childEvent.emit(value);
}
ngOnInit() {
}
}
If the components do not have a parent/child relationship, a shared service can be used, say, SharedService which has a BehavioralSubject, that emits value from either component, and the other component can then catch the changed value.
Eg:
import { Injectable } from '#angular/core';
import { BehaviorSubject } from "rxjs/BehaviorSubject";
#Injectable()
export class SharedService {
comp1Val: string;
_comp1ValueBS = new BehaviorSubject<string>('');
comp2Val: string;
_comp2ValueBS = new BehaviorSubject<string>('');
constructor() {
this.comp1Val;
this.comp2Val;
this._comp1ValueBS.next(this.comp1Val);
this._comp2ValueBS.next(this.comp2Val);
}
updateComp1Val(val) {
this.comp1Val = val;
this._comp1ValueBS.next(this.comp1Val);
}
updateComp2Val(val) {
this.comp2Val = val;
this._comp2ValueBS.next(this.comp2Val);
}
And component1 as follows :
import { Injectable } from '#angular/core';
import { BehaviorSubject } from "rxjs/BehaviorSubject";
#Injectable()
export class SharedService {
comp1Val: string;
_comp1ValueBS = new BehaviorSubject<string>('');
comp2Val: string;
_comp2ValueBS = new BehaviorSubject<string>('');
constructor() {
this.comp1Val;
this.comp2Val;
this._comp1ValueBS.next(this.comp1Val);
this._comp2ValueBS.next(this.comp2Val);
}
updateComp1Val(val) {
this.comp1Val = val;
this._comp1ValueBS.next(this.comp1Val);
}
updateComp2Val(val) {
this.comp2Val = val;
this._comp2ValueBS.next(this.comp2Val);
}
Component 2 :
import { Component, AfterContentChecked } from '#angular/core';
import { SharedService } from "../../common/shared.service";
#Component({
selector: 'app-component2',
templateUrl: './component2.component.html',
styleUrls: ['./component2.component.css']
})
export class Component2Component implements AfterContentChecked {
comp1Val: string;
comp2Val: string;
constructor(private sharedService: SharedService) {
this.sharedService.comp2Val = "Component 2 initial value";
}
ngAfterContentChecked() {
this.comp1Val = this.sharedService.comp1Val;
}
addValue(str) {
this.sharedService.updateComp2Val(str);
}
}
You can find more on different types of subjects here

Related

Reloading multiple child component from parent in Angular 14

I have a problem with reloading my child component from parent component in Angular.
Here is an example of what I want to do.
This is my child component
import { Component } from "#angular/core";
#Component({
selector: "app-child",
template: `<p> {{ticks}} </p>`,
styleUrls: ["./child.component.css"]
})
export class ChildComponent {
ticks = Date.now().valueOf();
constructor() {}
update(): void {
this.ticks = Date.now().valueOf();
}
}
And here is my parent component:
import { Component, OnInit, ViewChild } from '#angular/core';
import { ChildComponent } from './../child/child.component';
#Component({
selector: 'app-parent',
templateUrl: './parent.component.html',
styleUrls: ['./parent.component.css'],
})
export class ParentComponent implements OnInit {
#ViewChild(ChildComponent, { static: false }) childC: ChildComponent;
showChild: boolean = true;
constructor() {}
ngOnInit() {}
onUpdateChild() {
this.childC.update();
}
}
Parent Component HTML :
<p>
parent works!
<button (click)="onUpdateChild()">update</button>
<app-child *ngIf="showChild"></app-child>
<app-child *ngIf="showChild"></app-child>
</p>
The main problem is that if I use my child component multiple time, and trying to click on “update” button, it just updates one of my child component that is used in parent component, but I want to update all same child component in parent component, here is what happens when you click on “update” button, only first value will change, not both.
How can I fix it ?!?
You can use #ViewChildren and QueryList to do what you are looking for.
#ViewChildren(ChildComponent) childrenC!: QueryList<ChildComponent>;
And your function would look like:
onUpdateChild() { //I would rename it to onUpdateChildren
if(this.childrenC) {
this.childrenC.forEach((childC: ChildComponent) => {
this.childC.update();
});
}
}
If you wanted your child component to update on it's own - as stated by a comment to your original post - this is an example of what you could do so you wouldn't even need the update button:
import { Component, OnInit } from "#angular/core";
#Component({
selector: "app-child",
template: `<p> {{ticks}} </p>`,
styleUrls: ["./child.component.css"]
})
export class ChildComponent implements OnInit {
ticks = Date.now().valueOf();
constructor() {}
ngOnInit(): void {
setInterval(() => {
this.ticks = Date.now().valueOf();
}, 1000); //updates every 1 second
}
}
Another option you can do without using a button is to use #Input with the ticks property that updates the value from the parent through an input.

How to pass data from child to parent?

I need to pass one variable, that is inside my child component, to parent page.
This variable that I am trying to pass, is the array result of Barcode Scanner.
And I need to pass it to parent to send to API.
childComponent.ts
this.consultList;
parentComponent.ts
export class ParentComponent implements OnInit {
#Input() consultList: any[] = [];
testCall() {
console.log('Test Consult: ', this.consultList;
}
Here is an example stackblitz project to test parent-child data transfer, using #Input() and #Output()mechanism
import { Component, EventEmitter, Input, Output } from '#angular/core';
#Component({
selector: 'child',
template: `
<h1>Hello {{ name }}! This is child component</h1>
<button (click)="sendEventToParent()">Send data to parent</button>
`,
styles: [
`
h1 {
font-family: Lato;
}
`
]
})
export class ChildComponent {
#Input() name: string;
#Output() eventFromChild: EventEmitter<string> = new EventEmitter();
sendEventToParent(): void {
this.eventFromChild.emit('data from child');
}
}
here is the parent component html called child
<child name="{{ name }}" (eventFromChild)="onEvent($event)"></child>
<h1>This is parent component</h1>
<p>{{dataFromChild}}</p>
and event bindin like that
import { Component, VERSION } from '#angular/core';
#Component({
selector: 'my-app',
templateUrl: './app.component.html',
styleUrls: ['./app.component.css']
})
export class AppComponent {
name = 'Angular ' + VERSION.major;
dataFromChild = '';
onEvent(event): void {
this.dataFromChild = event;
}
}
What you are thinking of is called an abstract class. An abstract class can define abstract properties just like an interface, abstract methods just like an interface, and unlike an interface it can actually implement methods. You cannot initialize an abstract class, but you can inherit code for re-use from it.
https://codesandbox.io/s/patient-breeze-h4s3t?file=/src/index.ts
abstract class Parent {
abstract someProperty: string;
someCall() {
console.log(this.someProperty);
}
}
class ChildOne extends Parent {
someProperty = "I am child one";
}
class ChildTwo extends Parent {
someProperty = "I am child two";
}
const one = new ChildOne();
const two = new ChildTwo();
one.someCall(); // "I am child one";
two.someCall(); // "I am child two";

Initial counter value not displaying on ChangeDetectionPush strategy

I am writing a simple counter. It has start,stop, toggle functionality in parent (app) and displaying changed value in child (counter) component using ChangeDetectionStrategy.OnPush.
Issue I am facing is not able to display initial counter value in child component on load.
Below are screenshot and code.
app.component.ts
import { Component } from '#angular/core';
import {BehaviorSubject} from 'rxjs';
#Component({
selector: 'app-root',
template: `<h1>Change Detection</h1>
<button (click)="start()">Start</button>
<button (click)="stop()">Stop</button>
<button (click)="toggleCD()">Toggle CD</button>
<hr>
<counter [data]="data$" [notifier]="notifier$"></counter>`,
})
export class AppComponent {
_counter = 0;
_interval;
_cdEnabled = false;
data$ = new BehaviorSubject({counter: 0});
notifier$ = new BehaviorSubject(false);
start() {
if (!this._interval) {
this._interval = setInterval((() => {
this.data$.next({counter: ++this._counter});
}), 10);
}
}
stop() {
clearInterval(this._interval);
this._interval = null;
}
toggleCD(){
this._cdEnabled = !this._cdEnabled;
this.notifier$.next(this._cdEnabled);
}
}
counter.component.ts
import {Component, Input, ChangeDetectionStrategy, OnInit, ChangeDetectorRef} from '#angular/core';
import {Observable} from 'rxjs/index';
#Component({
selector: 'counter',
template: `Items: {{_data.counter}}`,
changeDetection: ChangeDetectionStrategy.OnPush
})
export class CounterComponent implements OnInit {
#Input() data: Observable<any>;
#Input() notifier: Observable<boolean>;
_data: any;
constructor(private cd: ChangeDetectorRef) {}
ngOnInit() {
this.data.subscribe((value) => {
/**
Below this._data.counter is showing 0 in console.log but
not in template
**/
this._data = value;
this.cd.markForCheck();
});
this.cd.detach();
this.notifier.subscribe((value) => {
if (value) {
this.cd.reattach();
} else {
this.cd.detach();
}
});
}
}
I'm using Angular 6.1.0
your AppComponent data$ is a BehaviorSubject, which you have given an initial value. your CounterComponent data expects an Observable, which you subscribe to. The defaulted BehaviorSubject does not fire until it changes. to get the value you have to query it upon load:
#Input() data: BehaviorSubject<any>;
ngOnInit() {
this._data = this.data.value; // get the initial value from the subject
this.data.subscribe((value) => {
this._data = value;
this.cd.markForCheck();
}
);
should do the trick.

Angular - How can I toggle the visibility of an element in a component from another component?

I have the following scenario in my Angular app:
A component MainDashboardComponent that is visible when I have the route /. Obviously I have the <router-outlet> tag in my app.component.html file, which looks like this:
<app-side-menu></app-side-menu>
<div class="main-container">
<div class="content">
<router-outlet></router-outlet>
</div>
</div>
As you can see I have a SideMenuComponent I use to have a side menu on all my routes. In MainDashboardComponent I have a method that for some reason needs to toggle a chat element that is situated on the side menu.
Inside the SideMenuComponent I have a method that handles the visibility toggle for the chat element and it works as expected. How can I call this method from my MainDashboardComponent and toggle the chat element from there?
What I tried with no success
I tried to inject the SideMenuComponent inside my MainDashboardComponent but, though the method toggleChat() is called, the element doesn't change it's visibility. Looks like I have a kind of multiple instance of the same component I guess...
Can you please help me with this? Thank you!
MainDashboardComponent
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-main-dashboard',
templateUrl: './main-dashboard.component.html',
styleUrls: ['./main-dashboard.component.scss']
})
export class MainDashboardComponent implements OnInit {
constructor() { }
ngOnInit() {}
setFocus(id) {
// here I'd like to call SideMenuComponent togglechat() ...
}
}
SideMenuComponent
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-side-menu',
templateUrl: './side-menu.component.html',
styleUrls: ['./side-menu.component.scss']
})
export class SideMenuComponent implements OnInit {
showChat: boolean;
constructor() {
this.showChat = false;
}
ngOnInit() {
}
toggleChat() {
this.showChat = !this.showChat;
}
}
To communicate between different components, there are different ways.
If you want to communicate between parent and child component, you can use EventEmitter to emit event from child component and handle the event in your parent component
If you want to communicate between any components, you can use Service and implement communication with the help of EventEmitter or Subject/BehaviorSubject
In your case, we can create a service, myService.ts and declare and eventEmitter
.service.ts
#Injectable()
export class AppCommonService {
toggle : EventEmitter<boolean> = new EventEmitter<boolean>()
}
mainDashboard.component.ts
constructor(private myService : myService){}
chatStatus : boolean = false;
ngOnInit(){
this.myService.toggle.subscribe(status=>this.chatStatus = status);
}
toggleChat(){
this.myService.toggle.emit(!this.chatStatus);
}
sideMenu.component.ts
constructor(private myService : myService){}
chatStatus : boolean = false;
ngOnInit(){
this.myService.toggle.subscribe(status=>this.chatStatus = status);
}
Generally this is the domain of a service!
Just create a service and add the "showCat" property.
Inject the service into both components
Alter SideMenuComponent to:
toggleChat() {
this.myService.showChat = !this.myService.showChat;
}
Alter MainDashboardComponent, also use this.myService.showChat to show / hide your chat window
Service TS
#Injectable()
export class MyService{
showCat:boolean = true
}
MainDashboardComponent
toggleChat() {
this.myService.showChat = !this.myService.showChat;
}
SideMenuComponent
chatVisiblity = this.myService.showCat //<-- bind this to the element attribute
You could efficiently use child to parent communication in this scenario. You'll need to create a custom event using angular's EventEmitter in your SideMenuComponent and use it in your MainDashboardComponent.
So, here is some code that may help you -
// SideMenuComponent
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-side-menu',
templateUrl: './side-menu.component.html',
styleUrls: ['./side-menu.component.scss']
})
export class SideMenuComponent implements OnInit {
#Output() valueChange = new EventEmitter();
showChat: boolean;
constructor() {
this.showChat = false;
}
ngOnInit() {
}
toggleChat() {
this.showChat = !this.showChat;
this.valueChange.emit(this.showChat);
}
}
// MainDashboardComponent
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-main-dashboard',
template: `<app-side-menu (valueChange)='setFocus($event)'></app-side-menu>`
styleUrls: ['./main-dashboard.component.scss']
})
export class MainDashboardComponent implements OnInit {
constructor() { }
ngOnInit() { }
setFocus(event) {
// check for required input value
console.log(event);
}
}
Refer these tutorials if required -
https://dzone.com/articles/understanding-output-and-eventemitter-in-angular,
https://angular-2-training-book.rangle.io/handout/components/app_structure/responding_to_component_events.html

Pass changing array to child component #Input field

I am trying to pass an array to a child component. The array is being defined in the subscribe method of a parent component's onInit lifecycle hook.
Parent component:
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'selector-parent',
templateUrl: 'parent.component.html'
})
export class ParentComponent implements OnInit {
array: [];
constructor() { }
ngOnInit() {
this.appDataService.getValues()
.subscribe(
value => {
value.item
.filter(loaded => !this.array.some(existing => existing.key === loaded.key))
.forEach(loaded => { this.array.push(loaded) })
}
)
}
}
Child component:
import { Component, OnInit } from '#angular/core';
#Component({
selector: '[selector-child]',
templateUrl: 'child.component.html'
})
export class ChildComponent implements OnInit {
#Input() inputArray: [];
constructor() { }
ngOnInit() {
console.log(this.inputArray)
}
}
Binding is: <tr selector-child [inputArray]="array"></tr>
Unfortunately, the console log on the inputArray is turning up undefined. I've tried using ngOnChanges in the child component but for some reason, it won't recognize the change in the parent. Thinking of using a service to pass the data if there isn't a simpler way to solve the problem.
You have to initialize the array in your parent component:
array: [] = [];
I don't see ngOnChanges in your child component. Also, make sure you do it as how it specified in the angular docs. https://angular.io/guide/component-interaction#intercept-input-property-changes-with-ngonchanges

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