#Input property is not being updated second time - javascript

I'm creating a reusable component which can be shown from any external component, but can be hidden using a function in same component, but somehow the property change in parent component is not updating child.
Here is the stackblitz for the same.
https://stackblitz.com/edit/angular-hfjkmu
I need "Show" button should show the component all the time and I can hide the component using "hide" button any time.

you need sync value from child to parent using Output
#Input()
show = false;
#Output()
showChange = new EventEmitter<boolean>();
constructor() { }
ngOnInit() {
}
hide(){
this.show = false;
this.showChange.emit(this.show);
}
<app-show-hide [(show)]="show"></app-show-hide>
The show property from child do not pointing to same prop in the parent comp, because it's primitive value.
I don't recommend to modify data that not belong to child component (reference type, eg: object, array), it can lead to unexpected behavior.
Online demo with reference type (be careful when modify ref type): https://stackblitz.com/edit/angular-vhxgpo?file=src%2Fapp%2Fshow-hide-obj%2Fshow-hide-obj.component.tsenter link description here

You have the problem because your child component modify Input value within your child component scope so no way parent component know the data is change
Your child component
export class ShowHideComponent implements OnInit {
#Input('show') show: boolean;
#Output() updateShowValue: EventEmitter<any> = new EventEmitter<
any
>();
constructor() { }
ngOnInit() {
console.log(this.show);
}
hide() {
this.updateShowValue.emit(!this.show);
}
}
In the app.component.html
<app-show-hide [show]="show" (updateShowValue)="update($event)"></app-show-hide>
And app.component.ts
export class AppComponent implements OnInit {
show:boolean = false;
ngOnInit() {
this.show = false;
console.log(this.show)
}
showComp(){
this.show = !this.show;
}
update(event) {
this.show = event;
}
}

You need to add an #Output in your child component, when you click the hide button (in the child component) you need to notify your parent component and change the value of show variable to false, this is done with the EventEmitter.
Changes to made are :
ShowHideComponent.ts
import { Component, OnInit, Input, Output, EventEmitter } from '#angular/core';
#Component({
selector: 'app-show-hide',
templateUrl: './show-hide.component.html'
})
export class ShowHideComponent {
#Input('show') show : boolean;
#Output('') hideEE = new EventEmitter();
constructor() { }
hide(){
this.hideEE.emit(false);
}
}
AppComponent.ts
import { Component,OnInit } from '#angular/core';
#Component({
selector: 'my-app',
templateUrl: './app.component.html'
})
export class AppComponent {
show:boolean = false;
}
appComponent.html
<button type="button" (click)="show = true">Show</button>
<app-show-hide [show]="show" (hideEE)="show = $event"></app-show-hide>
stackblitz Link

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.

Angular: Check when Output Variable in Component Changes?

How do I check if Output in Component changes? Then run another method
Here is Parent component,
After it gets data from Child, want to immediately run another event.
Parent HTML:
<div>
Address Type:*
<app-address-type-dropdown (selectedItemOutput) = "test"></app-address-type-dropdown>
</div>
Parent Typescript:
Goal: When value is outputted, detect changes in this parent, and write console command.
export class AddressFormatheaderFormComponent implements OnInit {
constructor() { }
public test: any;
public sayHi(){
console.log(this.test);
}
ngOnInit() {
}
}
You can do so by creating another function, an event handler essentially. So when your child component <app-address-type-dropdown> emits a value, this event handler will take care of what to do next.
E.g. onNewItemSelect($event) is the event handler.
<div>
Address Type:*
<app-address-type-dropdown (selectedItemOutput)="onNewItemSelect($event)"></app-address-type-dropdown>
</div>
export class AddressFormatheaderFormComponent implements OnInit {
constructor() { }
public test: any;
ngOnInit() {
}
onNewItemSelect(itemSelected){
this.test = itemSelected;
console.log(this.test);
//do something else
}
}
Do have read on this section of of Angular official docs on component interaction for more information.
I think you will need EventEmitter so in child component, when value changes, it will emit event and in parent component, it will detect changes and call parent function.
Something like let's say your child component.
import { Component, EventEmitter, Output } from '#angular/core';
#Component({
selector: 'app-address-type-dropdown,
template: `<button class='btn btn-primary' (click)="valueChanged()">Click me</button> `
})
export class AppAddressTypeDropdown{
#Output() selectedItemOutput= new EventEmitter();
Counter = 0;
valueChanged() { // You can give any function name
this.counter = this.counter + 1;
this.selectedItemOutput.emit(this.counter);
}
}
And in parent html, just try update call slightly. Please call any function to know when it changes.
<app-address-type-dropdown (selectedItemOutput) = "changeDetect($event)"></app-address-type-dropdown>
export class AddressFormatheaderFormComponent implements OnInit {
constructor() { }
public test: any;
public sayHi(){
console.log(this.test);
}
ngOnInit() {
}
changeDetect(counter){
console.log(counter);
//do something here
}

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

How to refresh one component (nav-bar) when button is clicked from another component?

I want to reload component after a button click from another component Angular 6.
As #MariyamMohammedJalil said you can use an EventEmitter to trigger the update of your first component.
See following sample:
first.component.ts
#Component({
selector: 'first-component',
template: '<div>{{label}}</label>
})
export class FirstComponent {
#Input() update: EventEmitter<string>;
label = 'First Component';
constructor() {}
ngOnInit() {
if (this.update) {
// Subscribe to the event emitter to receive an update event
this.update.subscribe((value: string) => {
this.refresh(value);
})
}
}
refresh(value: string) {
// Do your stuff here
this.label = value;
}
}
second.component.ts
#Component({
selector: 'second-component',
template: '<button (click)="updateFirstCmp()">Update First Component</button>'
})
export class SecondComponent {
#Input() update: EventEmitter<string>;
constructor(){}
updateFirstCmp() {
// Emit an event to update your first component
this.update.emit('Updated First Component');
}
}
And for example you should add following to your app.component.ts:
updateEventEmitter: EventEmitter<string>;
constructor() {
...
this.updateEventEmitter = new EventEmitter();
}
And in your app.component.html:
<first-component [update]="updateEventEmitter"></first-component>
<second-component [update]="updateEventEmitter"
Another way do solve your problem can be to enter the first.component as input parameter to the second.component to call the refresh function directly without EventEmitter. See following sample:
app.component.html
<first-component #firstComponent></first-component>
<second-component [firstCmp]="firstComponent"></second-component>
second.component.ts
#Component({
selector: 'second-component',
template: '<button (click)="updateFirstCmp()">Update First Component</button>'
})
export class SecondComponent {
#Input() firstCmp: FirstComponent;
constructor(){}
updateFirstCmp() {
// Update the first component directly
this.firstCmp.refresh('Updated First Component');
}
}
With this sample you don't need to subscribe to an update event, because you're not using an EventEmitter.

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