[Angular Directive] Implement Structural Directive Data Binding with Context in Angular

Just like in *ngFor, you're able to pass in data into your own structural directives. This is done by declaring the variable using a let statement then passing context into the createEmbeddedView call.

We know *ngFor we did like this:

*ngFor="let message of messages"

So how can we also do like this?

Remember that 

<h1 *three="let messages"> 

<!-- Equal to --> 

<template let-messages></template>

import {Directive, Input, TemplateRef, ViewContainerRef} from "@angular/core";
@Directive({
  selector: '[three]'
})
export class ThreeDirective {
  @Input() set three(value) {
    let num = 3;

    while (num--) {
      const message = {
        to: "People" + Math.random(),
        message: "Hello" + Math.random()
      };
      this.view.createEmbeddedView(this.template, {
        $implicit: message
      })
    }
  }

  constructor(private template: TemplateRef<any>, private view: ViewContainerRef) {

  }
}

There to avoid change detection problem (value changed after compoennt inited). We need to point out after 'three' as an input.

<h2 *three="let message">{{message.to}} - {{message.message}}</h2>