Develop Reference

Observable input is null in child component. Why?

I am facing a situation I don't understand. I have a parent component (app.component in the example) that gets its data from an API as an observable
This data is then passed down to the child (hello.component) using the async pipe.
That child then receives the input, but when ngOnInit runs in the child, the input is null.
I don't understand why, and I don't know how to make it so that the input is the actual returned value from the API instead. The call to detectChanges() in app.component was a desperate attempt to trigger change detection in the child but that doesn't re-run ngOnInit so it's kinda moot. I left it there because that's how the actual code I'm working with looked like.
I know this code is terrible.I didn't write it. Unfortunately, the component I'm working with is like that and I can't refactor it because, you guessed it, there are no unit tests. I'm working on cleaning it all up, but for now I have to reuse that component the way it is.
Stackblitz: https://stackblitz.com/edit/angular-ivy-rw1xte?devtoolsheight=33&file=src/app/hello.component.ts
// app.component.ts
import { ChangeDetectorRef, Component, VERSION } from "#angular/core";
import { interval, Observable, of } from "rxjs";
import { mapTo, tap } from "rxjs/operators";
#Component({
selector: "my-app",
templateUrl: "./app.component.html",
styleUrls: ["./app.component.css"]
})
export class AppComponent {
public name$: Observable<any> = of({});
constructor(private cdRef: ChangeDetectorRef) {}
public ngOnInit() {
this.name$ = interval(3000).pipe(
mapTo(() => {
first: "Eunice";
}),
tap(() => this.cdRef.detectChanges())
);
}
}
<!-- app.component.html -->
<hello [name]="name$ | async"></hello>
<p>
Start editing to see some magic happen :)
</p>
// hello.component.ts
import { Component, Input } from "#angular/core";
#Component({
selector: "hello",
template: `
<div *ngIf="name">
<h1>Hello {{ this.name.first }}!</h1>
<h1>{{ greetings }}</h1>
</div>
`,
styles: [
`
h1 {
font-family: Lato;
}
`
]
})
export class HelloComponent {
#Input() name: { first?: string }
public greetings: string = "";
public firstName: string = "";
public async ngOnInit() {
console.log('name:',this.name); // name: null
if (this.name) {
// this conditional is always false because this.name is always null
// and so this never runs.
console.log("got name");
this.firstName = this.name.first || "fallback";
this.greetings = await new Promise(resolve =>
resolve("how do you do, ${firstName}?")
);
}
}
}

this.name$ = interval(3000).pipe(
mapTo({
first: "Eunice"
}),
tap(() => this.cdRef.detectChanges())
);
Please fix it like the above. mapTo doesn't need to accept a function. It didnt make an error for you? :)
Also, the name input is null right when the hello component is mounted.
You need to check the name in ngOnChanges or you need to mount the hello component only when the name is available.
For example:
<hello *ngIf="name$ | async as name" [name]="name"></hello>
Or
public async ngOnChanges() {
console.log('name:', this.name); // name: null
if (this.name) {
...
}
}

Angular - Structural directive with embedded view does not pass children to ng-template

I've got a structural directive that creates an embedded view by looking up a template ref using ng-template. My problem is that from this parent component (with structural directive), I cannot pass down children.
Parent component with structural directive
import { ViewChild, Component, OnInit, ElementRef } from "#angular/core";
import { TestJsonService } from "../../services/test-json.service";
#Component({
selector: "xfr-json-renderer",
template: `
<template-lookup></template-lookup>
<div class="NA-TEMPLATE-CHOOSER" *replaceWith="'flexCol'">
<div>Why can't i pass this down to the child?</div>
</div>
`,
styleUrls: ["./json-renderer.component.css"],
})
export class JsonRendererComponent implements OnInit {
#ViewChild("childTemplate") childTemplate;
constructor(el: ElementRef, json: TestJsonService) {}
ngOnInit(): void {}
ngAfterViewInit() {}
}
Child component
import { Injectable, TemplateRef, Component, ViewChild } from "#angular/core";
#Injectable()
export class TemplateStore {
templates = new Map<string, TemplateRef<any>>();
}
#Component({
selector: "template-lookup",
template: `
<ng-template #flexRow></ng-template>
<ng-template #flexCol><xfr-flex-col>
// I want to pass the children into here
</xfr-flex-col></ng-template>
`,
})
export class TemplateLookup {
#ViewChild("flexRow") flexRowTemplate;
#ViewChild("flexCol") flexColTemplate;
constructor(private service: TemplateStore) {}
ngAfterViewInit() {
this.service.templates.set("flexRow", this.flexRowTemplate);
this.service.templates.set("flexCol", this.flexColTemplate);
}
}
Structural directive
import { ViewContainerRef } from "#angular/core";
import { TemplateStore } from "./../services/composite-template.service";
import { Directive, Input } from "#angular/core";
#Directive({
selector: "[replaceWith]",
})
export class CompositeTemplateDirective {
#Input() replaceWith: "flex-col" | "flex-row";
constructor(private service: TemplateStore, private view: ViewContainerRef) {}
ngAfterViewInit() {
this.view.createEmbeddedView(this.service.templates.get(this.replaceWith));
}
}

The problem is that you need to use internal API for that, what is not the best thing. I would use it until I stay with the same angular version and would test it before every update - then should work stable.
I was able to do the injection with Angular 9, quite sure a similar solution (but different internal API) can be applied for other angular versions.
The main thing for the injection - where to inject the content, in components we could use ng-content, but here it wouldn't work, because we have different component contexts. In this case we could use <ng-template [ngTemplateOutlet]></ng-template> to tell the script where we want the injection.
here you can find a live demo: https://codesandbox.io/s/nifty-wright-335bm?file=/src/app/json-renderer.component.ts
CompositeTemplateDirective
import {NgTemplateOutlet} from '#angular/common';
import {AfterViewInit, Directive, Input, TemplateRef, ViewContainerRef} from '#angular/core';
import {TemplateStore} from 'src/app/TemplateLookup/TemplateLookup';
#Directive({
selector: '[replaceWith]',
})
export class CompositeTemplateDirective implements AfterViewInit {
#Input() replaceWith: 'flex-col' | 'flex-row';
constructor(
private service: TemplateStore,
private view: ViewContainerRef,
private templateRef: TemplateRef<any>,
) {
}
public ngAfterViewInit(): void {
const wrapper = this.service.templates.get(this.replaceWith);
const source = this.templateRef;
const view: any = this.view.createEmbeddedView(wrapper);
let directive: NgTemplateOutlet;
const nodes: Array<any> = view._lView ? view._lView : view._view && view._view.nodes ? view._view.nodes : [];
for (const node of nodes) {
if (typeof node !== 'object') {
continue;
}
if (node instanceof NgTemplateOutlet) {
directive = node;
}
if (typeof node.instance === 'object' && node.instance instanceof NgTemplateOutlet) {
directive = node.instance;
}
}
if (directive) {
directive.ngTemplateOutlet = source;
directive.ngOnChanges({
ngTemplateOutlet: {
previousValue: null,
currentValue: source,
firstChange: true,
isFirstChange: () => true,
},
});
}
}
}
TemplateLookup
import {AfterViewInit, Component, Injectable, TemplateRef, ViewChild} from '#angular/core';
#Injectable()
export class TemplateStore {
templates = new Map<string, TemplateRef<any>>();
}
#Component({
selector: 'template-lookup',
template: `
<ng-template #flexRow>
<div>
flexRow template
</div>
</ng-template>
<ng-template #flexCol>
<div>
<div>wrap</div>
<ng-template [ngTemplateOutlet]></ng-template>
<div>wrap</div>
</div>
</ng-template>
`,
})
export class TemplateLookup implements AfterViewInit {
#ViewChild('flexRow', {static: false}) flexRowTemplate;
#ViewChild('flexCol', {static: false}) flexColTemplate;
constructor(
private service: TemplateStore,
) {
}
ngAfterViewInit() {
console.log('TemplateLookup:ngAfterViewInit');
this.service.templates.set('flexRow', this.flexRowTemplate);
this.service.templates.set('flexCol', this.flexColTemplate);
}
}

so the most pragmatic thing here seems to be to just put the child you want to pass as a child of the template-lookup component and use ng-content...
do this in the parent:
<template-lookup>
<div>I will pass to child</div>
</template-lookup>
<div class="NA-TEMPLATE-CHOOSER" *replaceWith="'flexCol'">
</div>
and this in the child:
<ng-template #flexRow></ng-template>
<ng-template #flexCol>
<xfr-flex-col>
<ng-content></ng-content>
</xfr-flex-col>
</ng-template>
and that will solve your problem / fulfill the stated requirements.
You could also consider a rewrite to your service to solve timing problems between templates being set and gotten once and for all:
import { Injectable, TemplateRef } from "#angular/core";
import {ReplaySubject} from 'rxjs';
import {map, filter, distinctUntilChanged} from 'rxjs/operators';
#Injectable({providedIn: 'root'}) // provide appropriately, root for example
export class TemplateStore {
private templates = new Map<string, TemplateRef<any>>();
private tmpSource = new ReplaySubject<Map<string, TemplateRef<any>>>(1);
setTemplate(key: string, template: TemplateRef<any>) {
this.templates.set(key, template);
this.tmpSource.next(this.templates)
}
getTemplate(key: string) {
return this.tmpSource.pipe(
map(tmpMap => tmpMap.get(key)),
filter(tmp => !!tmp),
distinctUntilChanged()
)
}
}
and make the associated changes in the directive and child components...
export class CompositeTemplateDirective implements OnInit, OnDestroy {
#Input() replaceWith: "flex-col" | "flex-row";
private sub: Subscription;
constructor(private service: TemplateStore, private viewContainer: ViewContainerRef) { }
ngOnInit() {
this.sub = this.service.getTemplate(this.replaceWith).subscribe(t => {
this.viewContainer.clear()
this.viewContainer.createEmbeddedView(t)
})
}
ngOnDestroy() {
this.sub.unsubscribe()
}
}
export class TemplateLookup {
#ViewChild("flexRow") flexRowTemplate;
#ViewChild("flexCol") flexColTemplate;
constructor(private service: TemplateStore) {}
ngAfterViewInit() {
this.service.setTemplate("flexRow", this.flexRowTemplate);
this.service.setTemplate("flexCol", this.flexColTemplate);
}
}
functioning example: https://stackblitz.com/edit/angular-ygdveu
it's been pointed out that this doesn't support nesting... so make the following adjustments and you can nest. in template lookup, you'll need to use the SkipSelf modifier in your constructor, and also provide the TemplateStore... in the case of no nesting, this will have no effect, SkipSelf just tells the injector to start looking for the service at the parent rather than at the component:
#Component({
selector: "template-lookup",
template: `
<ng-template #flexRow>FLEX ROW</ng-template>
<ng-template #flexCol>
FLEX COL
<div class="flex-col">
<ng-content></ng-content>
</div>
</ng-template>
`,
providers: [TemplateStore]
})
export class TemplateLookup {
#ViewChild("flexRow") flexRowTemplate;
#ViewChild("flexCol") flexColTemplate;
constructor(#SkipSelf() private service: TemplateStore) {}
ngAfterViewInit() {
this.service.setTemplate("flexRow", this.flexRowTemplate);
this.service.setTemplate("flexCol", this.flexColTemplate);
}
}
then you can nest to your hearts content like so:
<template-lookup>
<div>I can pass this to the child!</div>
<template-lookup>NESTED</template-lookup>
<div class="nested-content" *replaceWith="'flexCol'"></div>
</template-lookup>
<div class="NA-TEMPLATE-CHOOSER" *replaceWith="'flexCol'">
</div>
which is a little ugly, as you need to repeat the template-lookup component, but it does get the job done. This works by allowing the directive and template lookup to communicate with a different copy of the TemplateStore so you can nest different content.
working example of this variant: https://stackblitz.com/edit/angular-lpner2

How can I execute action after data-bind in Angular 2?

I'm developing an Angular 2 SPA. My application is composed by:
One component
One directive
I've builded one directive that format text input using onfocus and onblur events. On focus event remove dots to text value, on blur event add thousand dots to text value.
Following component's code:
<div>
<input id="input" [(ngModel)]="numero" InputNumber />
</div>
Following component's TypeScript code:
import { Component } from '#angular/core';
#Component({
selector: 'counter',
templateUrl: './counter.component.html'
})
export class CounterComponent {
numero: number;
public incrementCounter() {
}
ngOnInit() {
this.numero = 100100100;
}
}
Following directive's TypeScript code:
import { Directive, HostListener, ElementRef, OnInit } from "#angular/core";
#Directive({ selector: "[InputNumber]" })
export class InputNumber implements OnInit, OnChanges {
private el: HTMLInputElement;
constructor(private elementRef: ElementRef) {
this.el = this.elementRef.nativeElement;
}
ngOnInit(): void {
// this.el.value is empty
console.log("Init " + this.el.value);
this.el.value = this.numberWithCommas(this.el.value);
}
ngOnChanges(changes: any): void {
// OnChanging value this code is not executed...
console.log("Change " + this.el.value);
this.el.value = this.numberWithCommas(this.el.value);
}
#HostListener("focus", ["$event.target.value"])
onFocus(value: string) {
this.el.value = this.replaceAll(value, ".", "");
}
#HostListener("blur", ["$event.target.value"])
onBlur(value: string) {
this.el.value = this.numberWithCommas(value);
}
private numberWithCommas(x) {
return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ".");
}
private escapeRegExp(str) {
return str.replace(/([.*+?^=!:${}()|\[\]\/\\])/g, "\\$1");
}
private replaceAll(str, find, replace) {
return str.replace(new RegExp(this.escapeRegExp(find), 'g'), replace);
}
}
The following code works except that I need lost focus for show my number like "100.100.100". How can I perform this action on init data loading?
I add one example at this link: Plnkr example
Thanks

You can do this by using a Pipe which takes a boolean parameter that represents your focus/no focus action.
import { Pipe, PipeTransform } from '#angular/core';
#Pipe({name: 'dots'})
export class DotsPipe implements PipeTransform {
transform(value: number, hasFocus:boolean): any {
if(hasFocus){
return value.toString().replace(/\./g,'');
}else{
return value.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ".");
}
}
}
Then you have to apply the Pipe on your [ngModel] and use Angular events (focus) and (focusout) to change your variable.
<input [ngModel]="numero | dots : hasFocus" (focus)="hasFocus=true" (focusout)="hasFocus=false" (ngModelChange)="numero=$event" />

I think that your directive should implement ControlValueAccessor interface https://angular.io/docs/ts/latest/api/forms/index/ControlValueAccessor-interface.html
It is needed for writing model in your directive. ControlValueAccessor interface has writeValue(value: any) method that will be initially called.
So your writeValue method will be something like this:
private onChange: (_: any) => {};
...
writeValue(val) {
const editedValue = this.numberWithCommas(val);
this._onChange(val);
}
registerOnChange(fn: any) : void {
this._onChange = fn;
}

Angular2, evaluate template from string inside a component

It's possible evaluate template from string in a variable?. I need place the string in the component instead of the expression,
e.g.
template: "<div>{{ template_string }}</div>"
template_string contains: <b>{{ name }}</b>
and all should be evaluated to <div><b>My Name</b></div>
but I see <div>{{ template_string }}</div>
I need something like {{ template_string | eval }} or something else to evaluate the content of the variable on current context.
It's possible? I need something to use this approach because template_string can be changed when the component is used.
Edit1:
Angular Version: 4.0.3
E.g.
#Component({
selector: 'product-item',
template: `
<div class="product">{{ template }}</div>`,
})
export class ProductItemComponent {
#Input() name: string;
#Input() price: number = 0;
#Input() template: string = `{{ name }} <b>{{ price | currency }}</b>`;
}
Usage:
<product-item [name]="product.name" [price]="product.price"></product-item>
Expected: Product Name USD3.00
Output: {{ name }} <b>{{ price | currency }}</b>

You can create your own directive that will do it:
compile.directive.ts
#Directive({
selector: '[compile]'
})
export class CompileDirective implements OnChanges {
#Input() compile: string;
#Input() compileContext: any;
compRef: ComponentRef<any>;
constructor(private vcRef: ViewContainerRef, private compiler: Compiler) {}
ngOnChanges() {
if(!this.compile) {
if(this.compRef) {
this.updateProperties();
return;
}
throw Error('You forgot to provide template');
}
this.vcRef.clear();
this.compRef = null;
const component = this.createDynamicComponent(this.compile);
const module = this.createDynamicModule(component);
this.compiler.compileModuleAndAllComponentsAsync(module)
.then((moduleWithFactories: ModuleWithComponentFactories<any>) => {
let compFactory = moduleWithFactories.componentFactories.find(x => x.componentType === component);
this.compRef = this.vcRef.createComponent(compFactory);
this.updateProperties();
})
.catch(error => {
console.log(error);
});
}
updateProperties() {
for(var prop in this.compileContext) {
this.compRef.instance[prop] = this.compileContext[prop];
}
}
private createDynamicComponent (template:string) {
#Component({
selector: 'custom-dynamic-component',
template: template,
})
class CustomDynamicComponent {}
return CustomDynamicComponent;
}
private createDynamicModule (component: Type<any>) {
#NgModule({
// You might need other modules, providers, etc...
// Note that whatever components you want to be able
// to render dynamically must be known to this module
imports: [CommonModule],
declarations: [component]
})
class DynamicModule {}
return DynamicModule;
}
}
Usage:
#Component({
selector: 'product-item',
template: `
<div class="product">
<ng-container *compile="template; context: this"></ng-container>
</div>
`,
})
export class ProductItemComponent {
#Input() name: string;
#Input() price: number = 0;
#Input() template: string = `{{ name }} <b>{{ price | currency }}</b>`;
}
Plunker Example
See also
Angular 2.1.0 create child component on the fly, dynamically

not sure how you're building the template string
import { ..., OnInit } from '#angular/core';
#Component({
selector: 'product-item',
template: `
<div class="product" [innerHtml]='template_string'>
</div>`,
})
export class ProductItemComponent implements OnInit {
#Input() name: string;
#Input() price: number = 0;
#Input() pre: string;
#Input() mid: string;
#Input() post: string;
template_string;
ngOnInit() {
// this is probably what you want
this.template_string = `${this.pre}${this.name}${this.mid}${this.price}${this.post}`
}
}
<product-item [name]="name" [price]="price" pre="<em>" mid="</em><b>" post="</b>"></product-item>
the string can be built from outside the component, would still recommend something like ngIf to control dynamic templates though.

In Angular double curly braces {{}} are used to evaluation an expression in a component's template. and not work on random strings or dynamically added DOM elements. So one way of doing this is to use typescript string interpolation using ${}. check the rest of code to understand
#Component({
selector: 'product-item',
template: `
<div class="product" [innerHTML]="template"></div>`,
})
export class ProductItemComponent {
#Input() name: string;
#Input() price: number = 0;
#Input() template: string = `${ this.name } <b>${ this.price }}</b>`;
}

angular 4+ assign #Input for ngComponentOutlet dynamically created component

In Angular 4 to dynamically create a component you can use ngComponentOutlet directive: https://angular.io/docs/ts/latest/api/common/index/NgComponentOutlet-directive.html
something like this:
Dynamic component
#Component({
selector: 'dynamic-component',
template: `
Dynamic component
`
})
export class DynamicComponent {
#Input() info: any;
}
App
#Component({
selector: 'my-app',
template: `
App<br>
<ng-container *ngComponentOutlet="component"></ng-container>
`
})
export class AppComponent {
this.component=DynamicComponent;
}
How do I pass #Input() info: any; information in this template <ng-container *ngComponentOutlet="component"></ng-container> ?

Such a feature was discussed in the pull request for ngComponentOutlet but was dropped for now.
Even the componentRef shown currently in https://angular.io/docs/ts/latest/api/common/index/NgComponentOutlet-directive.html is not public and therefore not available https://github.com/angular/angular/blob/3ef73c2b1945340ca6bd21f1790260c88698ae26/modules/%40angular/common/src/directives/ng_component_outlet.ts#L78
I'd suggest you create your own directive derived from https://github.com/angular/angular/blob/3ef73c2b1945340ca6bd21f1790260c88698ae26/modules/%40angular/common/src/directives/ng_component_outlet.ts#L72
and assign values to inputs like shown in Angular 2 dynamic tabs with user-click chosen components
this.compRef.instance.someProperty = 'someValue';

With the help of the post of #Günter Zöchbauer I solved a similar problem this way - I hope you can adapt it somehow.
First I defined some interfaces:
// all dynamically loaded components should implement this guy
export interface IDynamicComponent { Context: object; }
// data from parent to dynLoadedComponent
export interface IDynamicComponentData {
component: any;
context?: object;
caller?: any;
}
then I implemented them inside of the dynamically loaded component
dynamicLoadedComponentA.ts
// ...
export class DynamicLoadedComponentA implements IDynamicComponent {
// ...
// data from parent
public Context: object;
// ...
After that I built a new component which is responsible for the magic. Important here is that I had to register all dyn. loaded components as entryComponents.
dynamic.component.ts
#Component({
selector: 'ngc-dynamic-component',
template: ´<ng-template #dynamicContainer></ng-template>´,
entryComponents: [ DynamicLoadedComponentA ]
})
export class DynamicComponent implements OnInit, OnDestroy, OnChanges {
#ViewChild('dynamicContainer', { read: ViewContainerRef }) public dynamicContainer: ViewContainerRef;
#Input() public componentData: IDynamicComponentData;
private componentRef: ComponentRef<any>;
private componentInstance: IDynamicComponent;
constructor(private resolver: ComponentFactoryResolver) { }
public ngOnInit() {
this.createComponent();
}
public ngOnChanges(changes: SimpleChanges) {
if (changes['componentData']) {
this.createComponent();
}
}
public ngOnDestroy() {
if (this.componentInstance) {
this.componentInstance = null;
}
if (this.componentRef) {
this.componentRef.destroy();
}
}
private createComponent() {
this.dynamicContainer.clear();
if (this.componentData && this.componentData.component) {
const factory: ComponentFactory<any> = this.resolver.resolveComponentFactory(this.componentData.component);
this.componentRef = this.dynamicContainer.createComponent(factory);
this.componentInstance = this.componentRef.instance as IDynamicComponent;
// fill context data
Object.assign(this.componentInstance.Context, this.componentData.context || {});
// register output events
// this.componentRef.instance.outputTrigger.subscribe(event => console.log(event));
}
}
}
here the usage of this shiny new stuff:
app.html
<!-- [...] -->
<div>
<ngc-dynamic-component [componentData]="_settingsData"></ngc-dynamic-component>
</div>
<!-- [...] -->
app.ts
// ...
private _settingsData: IDynamicComponent = {
component: DynamicLoadedComponentA,
context: { SomeValue: 42 },
caller: this
};
// ...

I think for now you can use
https://www.npmjs.com/package/ng-dynamic-component
It is made specifically for this issue