Angular2 child component as data

Question

Let's say I have two components: parent and child. The HTML would look like this:

<parent title="Welcome">
    <child name="Chris">Blue Team</child>
    <child name="Tom">Red Team</child>
</parent>

The final output would look like:

<h1>Welcome</h2>
<ul>
    <li><b>Chris</b> is on the Blue Team</li>
    <li><b>Tom</b> is on the Red Team</li>
</ul>

The parent component:

@Component({
  selector: 'parent',
  directives: [ChildComponent], // needed?
  template: `
    <h1>{{title}}</h1>
    <ul>
       <li *ngFor="#child of children()">{{child.content}}<li>
    </ul>`
})
export class ParentComponent {

    @Input() title;

    children() {
        // how?
    }

}

How do I access the child components from within the parent and get their content?

Also, I don't want the children to be automatically rendered. Depending on some conditions I may choose not to show certain children.

Thanks.

Answer 1

<ng-content>

For projecting content to an element (transclusion) you would need the <ng-content> element like

@Component({
  selector: 'parent',
  directives: [ChildComponent], // needed?
  template: `
    <h1>{{title}}</h1>
    <ul>
       <li *ngFor="letchild of children()">
         <ng-content></ng-content>
       </li>
    </ul>`
})

<ng-content select="xxx">

but that won't work for your use case because <ng-content> doesn't produce content, it only projects it (works as a placehoder where children are displayed within your components template.

Even though *ngFor would produce 3 <ng-content> elements, the children would only be displayed once in the first <ng-content> element.

<ng-content> allows to use selectors like

<ng-content select="[name=Chris]"></ng-content>

where a template like

<ul>
   <li>
     <ng-content select="[name=Chris]"></ng-content>
   </li>
</ul>`

would result in

<h1>Welcome</h2>
<ul>
    <li><b>Chris</b> is on the Blue Team</li>
</ul>

A more flexible and powerful approach explained in Binding events when using a ngForTemplate in Angular 2 (from @kemsky s comment)

<template>, @ViewChildren(), and *ngForTemplate

If you wrap the children in <template> tags you can access them using @ContentChildren() and insert them using *ngFor and *ngForTemplate.

I am using a little hack here with the inner *ngFor. There is a better approach work in progress (ngTemplateOutlet https://github.com/angular/angular/pull/8021 already merged)

@Component({
  selector: 'parent',
  template: `
    <h1>{{title}}</h1>
    <ul>
      <li *ngFor="let child of templates">
         <!-- with [child] we make the single element work with 
              *ngFor because it only works with arrays -->
         <span *ngFor="let t of [child]" *ngForTemplate="child"></span>
      </li>
    </ul>
    <div>children:{{children}}</div>
    <div>templates:{{templates}}</div>
    `
})
export class ParentComponent {

  @Input() title;
  @ContentChildren(TemplateRef) templates;
}

@Component({
    selector: 'my-app',
    directives: [ParentComponent],
    template: `
    <h1>Hello</h1>
<parent title="Welcome">
  <template><child name="Chris">Blue Team</child></template>
  <template><child name="Tom">Red Team</child></template>
</parent>    
    `,
})
export class AppComponent {}

Plunker example

See also How to repeat a piece of HTML multiple times without ngFor and without another @Component for more ngTemplateOutlet Plunker examples.

update Angular 5

ngOutletContext was renamed to ngTemplateOutletContext

See also https://github.com/angular/angular/blob/master/CHANGELOG.md#500-beta5-2017-08-29