angular之ng-template模板加载

<table id="producttable">
 <thead>
  <tr>
   <td>UPC_Code</td>
   <td>Product_Name</td>
  </tr>
 </thead>
 <tbody>
  <!-- 现有数据可以可选地包括在这里 -->
 </tbody>
</table>

<template id="productrow">
 <tr>
  <td class="record"></td>
  <td></td>
 </tr>
</template>

// 通过检查来测试浏览器是否支持HTML模板元素 
// 用于保存模板元素的内容属性。
if ('content' in document.createElement('template')) {

 // 使用现有的HTML tbody实例化表和该行与模板
 let t = document.querySelector('#productrow'),
 td = t.content.querySelectorAll("td");
 td[0].textContent = "1235646565";
 td[1].textContent = "Stuff";

 // 克隆新行并将其插入表中
 let tb = document.getElementsByTagName("tbody");
 let clone = document.importNode(t.content, true);
 tb[0].appendChild(clone);
 
 // 创建一个新行
 td[0].textContent = "0384928528";
 td[1].textContent = "Acme Kidney Beans";

 // 克隆新行并将其插入表中
 let clone2 = document.importNode(t.content, true);
 tb[0].appendChild(clone2);

} else {
 // 找到另一种方法来添加行到表，因为不支持HTML模板元素。
}

UPC_Code  Product_Name
1235646565 Stuff
0384928528 Acme Kidney Beans

<div ngIf="hero" >{{hero.name}}</div>

<ng-template [ngIf]="hero">
 <div>{{hero.name}}</div>
</ng-template>`

import {Directive, EmbeddedViewRef, Input, TemplateRef, ViewContainerRef} from '@angular/core';
@Directive({selector: '[ngIf]'})
export class NgIf {
 private _context: NgIfContext = new NgIfContext();
 private _thenTemplateRef: TemplateRef<NgIfContext>|null = null;
 private _elseTemplateRef: TemplateRef<NgIfContext>|null = null;
 private _thenViewRef: EmbeddedViewRef<NgIfContext>|null = null;
 private _elseViewRef: EmbeddedViewRef<NgIfContext>|null = null;

 constructor(private _viewContainer: ViewContainerRef, templateRef: TemplateRef<NgIfContext>) {
  this._thenTemplateRef = templateRef;
 }

 @Input()
 set ngIf(condition: any) {
  this._context.$implicit = this._context.ngIf = condition;
  this._updateView();
 }

 @Input()
 set ngIfThen(templateRef: TemplateRef<NgIfContext>) {
  this._thenTemplateRef = templateRef;
  this._thenViewRef = null; // clear previous view if any.
  this._updateView();
 }

 @Input()
 set ngIfElse(templateRef: TemplateRef<NgIfContext>) {
  this._elseTemplateRef = templateRef;
  this._elseViewRef = null; // clear previous view if any.
  this._updateView();
 }

 private _updateView() {
  if (this._context.$implicit) {
   if (!this._thenViewRef) {
    this._viewContainer.clear();
    this._elseViewRef = null;
    if (this._thenTemplateRef) {
     this._thenViewRef =
       this._viewContainer.createEmbeddedView(this._thenTemplateRef, this._context);
    }
   }
  } else {
   if (!this._elseViewRef) {
    this._viewContainer.clear();
    this._thenViewRef = null;
    if (this._elseTemplateRef) {
     this._elseViewRef =
       this._viewContainer.createEmbeddedView(this._elseTemplateRef, this._context);
    }
   }
  }
 }
}

export class NgIfContext {
 public $implicit: any = null;
 public ngIf: any = null;
}

 abstract get elementRef(): ElementRef;
 abstract createEmbeddedView(context: C): EmbeddedViewRef<C>;
}

<ng-template #tptest>
 <span>template test</span>
</ng-template>

@ViewChild('tptest') tptest: TemplateRef<any>;

export abstract class ViewContainerRef {
  /基于TemplateRef对象创建Embedded View(内嵌视图)，然后根据`index`指定的值，插入到容器中。 
  如果没有指定`index`的值，新创建的视图将作为容器中的一个视图插入。/ 
 abstract createEmbeddedView<C>(
   templateRef: TemplateRef<C>, //内嵌视图
   context?: C, index?: number): // 创建上下文
   EmbeddedViewRef<C>;
}

export class NgForOfContext<T> {
 constructor(
   public $implicit: T, public ngForOf: NgIterable<T>, public index: number,
   public count: number) {}

 get first(): boolean { return this.index === 0; }

 get last(): boolean { return this.index === this.count - 1; }

 get even(): boolean { return this.index % 2 === 0; }

 get odd(): boolean { return !this.even; }
}

<div ngFor="let hero of heroes; let i=index; let odd=odd">
 ({{i}}) {{hero.name}}
</div>


解析后

<ng-template ngFor let-hero [ngForOf]="heroes" let-i="index" let-odd="odd" >
 <div>({{i}}) {{hero.name}}</div>
</ng-template>