I have a angular component app-b that is used within a component app-a that is used in the app-component. The app-component has some content in app-a, app-a transcludes this with ng-content into app-b, app-b shows it with another ng-content - but how can I access this content within the component (and not it's template)?
I would think that ContentChild is the correct approach but appears to be wrong.
Example:
https://stackblitz.com/edit/angular-ddldwi
EDIT: Updated example
You cannot query by tag name with #ContentChild decorator. You can query either by template variable, component or directive selector.
app-a.component.html
<app-b>
<ng-content></ng-content>
<p #myContent>This is a content child for app-b.</p>
</app-b>
app-b.component.ts
import { Component, AfterContentInit, ContentChild } from '#angular/core';
#Component({
selector: 'app-b',
templateUrl: './b.component.html',
styleUrls: ['./b.component.css']
})
export class BComponent implements AfterContentInit {
#ContentChild('myContent') contentchild;
ngAfterContentInit() {
console.log(this.contentchild);
}
}
Live demo
I recommend sharing the data between components. For example, move your data (E.G. dummyName) into a service. Then add the service to each component (where you need the shared data).
Service:
import { Injectable } from '#angular/core';
#Injectable()
export class DataShareService {
public dummyName: String = 'one';
constructor() { }
}
Add the new service to app.module.ts:
providers: [DataShareService],
Child Component:
import { DataShareService } from './data-share.service';
import { Component } from '#angular/core';
#Component({
selector: 'app-child',
templateUrl: './child.component.html'
})
export class ChildComponent {
constructor(public ds: DataShareService) { }
toggle() {
this.ds.dummyName = this.ds.dummyName === 'one' ? 'two' : 'one';
}
}
Child Component template (html):
<p> {{ds.dummyName}}</p>
<button (click)="toggle()">Click Me to Toggle Value</button>
Parent Component:
import { Component, OnInit } from '#angular/core';
import { DataShareService } from './data-share.service';
#Component({
selector: 'app-root',
templateUrl: './app.component.html'
})
export class AppComponent {
constructor(public ds: DataShareService) {}
displayNumber() {
return this.ds.dummyName === 'one' ? 1 : 2;
}
}
Parent Component template (html):
<p> this is the parent component:</p>
<div> value as string: {{ ds.dummyName }} </div>
<div> value as number: <span [textContent]="displayNumber()"></span></div>
<hr>
<p> this is the child component:</p>
<app-child></app-child>
Note! The child component toggle() function demonstrates how you can change the data. The parent component displayNumber() function demonstrates how to use the data, independent of it's display (I.E. as just pure data).
This appears to be impossible due to a bug in Angular:
https://github.com/angular/angular/issues/20810
Further reference:
https://www.reddit.com/r/Angular2/comments/8fb3ku/need_help_how_can_i_access_an_already_transcluded/
Related
When I use #ViewChild I get the error that the component is not defined.
When I use #ViewChildren I get the error that the function from that component is not a function.
I am new to using child components in Angular so I'm not sure why it's doing this when I do have the child component defined in the parent component and when it's clearly a function in the child component.
I don't want to have to define every function from the child in the parent or else what's even the point of using a separate component.
Child Component
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-mood',
templateUrl: './mood.component.html',
styleUrls: ['./mood.component.css']
})
export class MoodComponent implements OnInit {
moodColors = ['red', 'orange', 'grey', 'yellow', 'green'];
constructor() { }
ngOnInit(): void {
}
chooseMood() {
alert(this.moodColors);
}
}
Parent Component (Relavant Part of Version with "ERROR TypeError: ctx_r3.mood is undefined")
import { Component, OnInit, ViewChild, ViewChildren } from '#angular/core';
import { ViewEncapsulation } from '#angular/core';
import { MoodComponent } from '../mood/mood.component';
#Component({
selector: 'app-calendar',
templateUrl: './calendar.component.html',
styleUrls: ['./calendar.component.css'],
encapsulation: ViewEncapsulation.None
})
export class CalendarComponent implements OnInit {
#ViewChild('mood') mood: MoodComponent = new MoodComponent;
Parent Component (Relavant Part of Version with "ERROR TypeError: ctx_r3.mood.chooseMood is not a function")
import { Component, OnInit, ViewChild, ViewChildren } from '#angular/core';
import { ViewEncapsulation } from '#angular/core';
import { MoodComponent } from '../mood/mood.component';
#Component({
selector: 'app-calendar',
templateUrl: './calendar.component.html',
styleUrls: ['./calendar.component.css'],
encapsulation: ViewEncapsulation.None
})
export class CalendarComponent implements OnInit {
#ViewChildren('mood') mood: MoodComponent = new MoodComponent;
Parent View
<h2 (click)="mood.chooseMood()"></h2>
You don't explicitly initialize view children via new.
Just use:
#ViewChild('mood') mood : MoodComponent;
If that doesn't work post a Stackblitz example which I can edit to resolve the issue.
Also, using ViewChild is more of an exception in Angular, and your use of it points to a probable design issue. More likely you child component should emit via an Output to the parent.
Regarding outputs, you can do something like this - though it is hard to give a precise answer without deeper knowledge of what you are trying to achieve:
export class MoodComponent implements OnInit {
#Input() moodId: string;
#Output() chooseMood = new EventEmitter<string>();
moodClicked(){
this.chooseMood.emit(moodId);
}
}
export class CalendarComponent implements OnInit {
moodChosen(string: moodId){
console.log(moodId);
}
}
// Calendar template:
<app-mood
moodId="happy"
(chooseMood)="moodChosen($event)"
></app-mood>
1 - you have to use this code
#ViewChild('mood') mood : MoodComponent;
when you are using #ViewChildren it will return list of items with the 'mood' name then you have to use this code
mood.first.chooseMood() ;
its better use ViewChildren when there is ngIf in your element
2- no need new keyword for initialize mood variable
it would be fill after ngOnInit life cycle fires
I have an object from parent component also received in a child component similar to this:
{
attribute: 'aaaa',
attribute2: [
{
value
},
{
value
},
{
value
},
]
}
This object is an #Input from a parent component. When I make changes to the objects inside the attribute2 array, I would like the child component detect that changes were made and then gets updated. As this is an object, I could'nt make it work, so I clone the entire object (this.objet = _.cloneDeep(this.object) in the parent component so then the child component detects that changes happened.
Is there any other way of doing this that does not clone the entire object? Thanks in advance
EDIT:
Child Component
export class ChildComponent implements OnInit, OnChanges {
#Input() public object: any;
}
html
<div>
<span>{{object.attribute}}</span>
<div *ngFor="let items of object.attribute2">{{item.value}}</div>
</div>
Parent Component
export class ParentComponent implements OnInit {
public object: any;
updateObject() {
this.object.attribute2[1] = 'Changed value';
this.object = _.cloneDeep(this.object);
}
}
html
<div>
<child-component [object]="object"></child-component>
</div>
An efficient way is to use EventEmitter and service communication to
trigger changes in the child component.
On way as mentioned by #Tony is to use ngOnChanges(). It is a good shortcut for detecting bounded properties change but as you add more and more bindings, using this hook will affect you application in the long run because it will run every time any of the bound property changes whether or not you desire it all the calls.
So for Service based communication, I've created an example on
Stackblitz:
https://stackblitz.com/edit/angular-fgut7t
Gist: https://gist.github.com/stupidly-logical/a34e272156b498513505127967aec851
In this example, I am binding an Array to the child component using #Input() an on addition of new data, the array is updated by the parent and the latest value is passed on the service which then emits this value. The child component subscribes to this value and the relevant code is executed.
The Service:
import { Injectable, EventEmitter } from '#angular/core';
#Injectable({
providedIn: "root"
})
export class DataService {
dataUpdated:EventEmitter<any> = new EventEmitter();
constructor() { }
setLatestData(data) {
this.dataUpdated.emit(data);
}
}
Child Component TS
import { Component, OnInit, Input } from '#angular/core';
import { DataService } from '../data-service.service';
#Component({
selector: 'app-child',
templateUrl: './child.component.html',
styleUrls: ['./child.component.css']
})
export class ChildComponent implements OnInit {
#Input() allData: [];
latestData: any;
constructor(private dataService: DataService) { }
ngOnInit() {
this.dataService.dataUpdated.subscribe((data) => {
this.latestData = data;
});
}
}
Child Component HTML
<p>
Latest Data: {{ latestData }}
</p>
<h3>List:</h3>
<li *ngFor="let data of allData">
{{ data }}
</li>
Parent Component TS
import { Component } from '#angular/core';
import { DataService } from './data-service.service'
#Component({
selector: 'my-app',
templateUrl: './app.component.html',
styleUrls: [ './app.component.css' ]
})
export class AppComponent {
name = 'Angular';
dataArr = [];
constructor(private dataService: DataService){}
onAddTimestamp() {
let timestamp = new Date();
this.dataArr.push(timestamp);
this.dataService.setLatestData(timestamp);
}
}
Parent Component HTML
<hello name="{{ name }}"></hello>
<p>
Start editing to see some magic happen :)
</p>
<button
(click)="onAddTimestamp()"
>
Add Timestamp
</button>
<app-child
[allData] = "dataArr"
></app-child>
Use the ngOnChanges() lifecycle method in your component.
ngOnChanges is called right after the data-bound properties have been
checked and before view and content children are checked if at least
one of them has changed.
Some like this
#Input() object: string;
ngOnChanges(changes: SimpleChanges) {
console.log(changes.object.currentValue);
// You can also use object.previousValue and
// object.firstChange for comparing old and new values
}
I am new to Angular 7 (2+) & trying my hands on #Input & #Output. However, passing data from Parent to Child component via #Input is understood & in place.
However, very basic on the other hand passing data from Child to Parent component via using #Output concept is understood & but the implementation is not getting right.
Here is what I am trying. When a button is clicked in the
Child component, a property in the parent component should be
converted to Upper case & displayed.
ChildComponent.ts
import { Component, OnInit, Input, Output, EventEmitter } from '#angular/core';
#Component({
selector: 'app-child',
templateUrl: './child.component.html',
})
export class ChildComponent implements OnInit {
#Input('child-name') ChildName: string;
#Output() onHit: EventEmitter<string> = new EventEmitter<string>();
constructor() { }
ngOnInit() {}
handleClick(name): void {
this.onHit.emit(name);
}}
ChildComponent.html
<h1> child works! </h1>
<button (click)="handleClick('eventEmitter')"> Click me! </button>
ParentComponent.ts
import { Component } from '#angular/core';
#Component({
selector: 'app-root',
templateUrl: './app.component.html',
})
export class AppComponent {
title = 'my-dream-app';
customerName: string = "";
catchChildEvent(e) {
console.log(e);
}}
ParentComponent.html
<div style="text-align:center">
<app-child [child-name]="HelloChild"></app-child>
//Trying to bind to Custom event of child component here
<b (onHit)="catchChildEvent($event)">
<i> {{customerName}} </i>
</b>
No error in console or binding
From the above snippet, when the button in Child Component is clicked the parent Component's property CustomerName should get the value & displayed?
Example: https://stackblitz.com/edit/angular-3vgorr
(onHit)="catchChildEvent($event)" should be passed to <app-child/>
<app-child [child-name]="HelloChild" (onHit)="catchChildEvent($event)"></app-child>
You are emitting event from app-child component so attach the handler for app-child component to make it work.
<div style="text-align:center">
<app-child (onHit)="catchChildEvent($event)" [child-name]="HelloChild"></app-child>
//Trying to bind to Custom event of child component here
<b>
<i> {{customerName}} </i>
</b>
And within the ts file update value of cutomerName property.
import { Component } from '#angular/core';
#Component({
selector: 'app-root',
templateUrl: './app.component.html',
})
export class AppComponent {
title = 'my-dream-app';
customerName: string = "";
catchChildEvent(e) {
this.customerName = e;
}
}
You should move (onHit)="catchChildEvent($event)" to app-child in parent html:
<app-child [child-name]="HelloChild"
(onHit)="catchChildEvent($event)>
</app-child>
I have created a component called Parent and Child. I want to display all the UI of ChildComponent to my ParentComponent.
child.component.ts
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-child',
templateUrl: './child.component.html',
styleUrls: ['./child.component.scss']
})
export class ChildComponent implements OnInit {
testContent = 'child component content...';
constructor() { }
ngOnInit() {
}
}
child.component.html
<p>{{testContent}}</p>
parent.component.ts
import { Component, OnInit } from '#angular/core';
#Component({
selector: 'app-admin',
templateUrl: './admin.component.html',
styleUrls: ['./admin.component.scss'],
directives: [ChildComponent]
})
export class AdminComponent implements OnInit {
constructor() { }
ngOnInit() {
}
}
parent.component.html
<div>
Lorem ipsum
<app-child></app-child>
</div>
I want to display the contents of child component inside parent component. However, I am encountering an error in Angular 4
"Object literal may only specify known properties, and 'directives'
does not exist in type 'Component'."
Do you have any idea what is the alternative property to add child component?
Remove directives from the parent component and add the child component to the module declarations array where the parent component lives.
Directives and pipes in #component are deprecated since angular RC6. Just remove it from the component.
#Component({
selector: 'app-admin',
templateUrl: './admin.component.html',
styleUrls: ['./admin.component.scss']
})
I have a my-alert-component which looks like this:
import { Component, OnInit,Input } from '#angular/core';
#Component({
selector: 'app-my-alert',
template: `
<h1 (click)="alert()">{{type}}</h1>
<ng-content></ng-content>
`
})
export class MyAlertComponent implements OnInit {
#Input() type: string = "Success";
alert(){
console.log("alert");
}
constructor() { }
ngOnInit() {
}
}
And in my app component, I am doing the following:
import { Component,ComponentRef,ComponentFactory,ViewContainerRef, ComponentFactoryResolver,ChangeDetectorRef, ViewChild, TemplateRef, ViewChildren, QueryList, AfterViewInit,ElementRef, ContentChild, AfterContentInit } from '#angular/core';
import { MyAlertComponent } from './my-alert.component';
#Component({
selector: 'app-root',
template: `
<app-my-alert>
<p #insideNgContentVar>A paragraph inside ng-content</p>
</app-my-alert>
<app-my-alert type="danger"></app-my-alert>
<app-my-alert type="success"></app-my-alert>
`
})
export class AppComponent implements AfterViewInit{
#ViewChildren(MyAlertComponent) alertComponents : QueryList<AlertComponent>;
#ContentChild('insideNgContentVar') insideNgContent:ElementRef;
ngAfterContentInit(){
console.log(this.insideNgContent.nativeElement.textContent);
}
ngAfterViewInit(){
this.alertComponents.forEach((alertComponentInstance) => console.log(alertComponentInstance));
}
}
This is pretty simple, I thought.
But the error I am getting is:
EXCEPTION: Error in :0:0 caused by: Cannot read property 'nativeElement' of undefined
What am I doing wrong?
EDIT
If in my-alert-component I do:
#Component({
selector: 'app-my-alert',
template: `
<h1 (click)="alert()">{{type}}</h1>
<ng-content></ng-content>
`
})
export class MyAlertComponent implements AfterContentInit,AfterViewInit {
#Input() type: string = "Success";
#ContentChild('insideNgContent') insideNgContentRef:ElementRef;
alert(){
console.log("alert");
}
ngAfterContentInit(){
console.log(this.insideNgContentRef.nativeElement.textContent);
}
And in my app component:
template: `
<app-my-alert>
</app-my-alert>
<app-my-alert type="danger">
<p #insideNgContent>A paragraph inside ng-content</p>
</app-my-alert>
<app-my-alert type="success"></app-my-alert>
`
After these changes also, something seems to be missing.
What is that?
I think you should be using #ViewChild here, as per this answer:
https://stackoverflow.com/a/34327754/5018962
So basically, ViewChild is going to look for components in the DOM that are defined in your component's template, but ContentChild will look for components defined as ng-content of your app-root component itself, but not ng-content of some child components. But in this case no one is using your app-root component and no one is going to inject any DOM there, so that's why you get undefined
EDIT.
It would work, if you added the following line to the app-my-alert component:
#ContentChild('insideNgContentVar') insideNgContent:ElementRef;
because that means, look at what is defined in the ng-content of app-my-alert. Hope that sheds some light on this topic