Angular利用内容投射向组件输入ngForOf模板的方法

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现在，我们写一个组件puppiesListCmp，用于显示小狗狗的列表：

//puppies-list.component.ts
@Component({
 selector: 'puppies-list',
 template: `
  <div *ngFor="let puppy of puppies">
   <span>{{puppy.name}}</span>
   <span>{{puppy.age}}</span>
   <span>{{puppy.color}}</span>
  </div>
`
})
export class puppiesListCmp{
 @Input() puppies: Puppy[];
}
interface Puppy {
 name: string,
 age: number,
 color: string
}

然后这样使用：

//app.component.ts
@Component({
 selector: 'my-app',
 template: `
  <puppies-list [puppies]="puppies"></puppies-list>
`
})
export class App{
 puppies = [
  {
   name: "sam",
   age: 0.6,
   color: "yellow"
  },
  {
   name: "bingo",
   age: 1.5,
   color: "black"
  }
 ]
}

效果就行这样：

但是，我希望我们的puppiesListCmp组件可以满足不同的需求，比如在数据不变的情况下只显示小狗狗的name和color，就像这样：

这就是本文的重点了。我们需要实现用户自定义模板！

现在我们不写死组件的模板了，而是让用户从外部输入!

首先，我们的组件模板：

<div *ngFor="let puppy of puppies">
   <span>{{puppy.name}}</span>
   <span>{{puppy.age}}</span>
   <span>{{puppy.color}}</span>
</div>

等价于：

<ng-template ngFor let-puppy [ngForOf]="puppies">
   <div>
    <span>{{puppy.name}}</span>
    <span>{{puppy.age}}</span>
    <span>{{puppy.color}}</span>
   </div>
</ng-template>

然后，用@ContentChild（关于@ContentChild可以查看这里，需FQ）获取到外部（相对puppiesListCmp组件而言）自定义模板，并赋给ngForTemplate。也就是说，这部分：

<div>
  <span>{{puppy.name}}</span>
  <span>{{puppy.age}}</span>
  <span>{{puppy.color}}</span>
</div>

不再像之前那样写死在组件里了，而是由使用者在父组件中自定义，然后利用Angular的内容投射（Content Projection），投射到puppiesListCmp组件里面。就像这样：

//puppies-list.component.ts
import { Component, Input, ContentChild, TemplateRef } from '@angular/core';
import { NgForOfContext } from '@angular/common';
@Component({
 selector: 'puppies-list',
 template: `
<ng-template ngFor let-puppy [ngForOf]="puppies" [ngForTemplate]="tpl"></ng-template>
`
})
export class puppiesListCmp{
 @Input() puppies: Puppy[];
 @ContentChild(TemplateRef) tpl: TemplateRef<NgForOfContext<Puppy
}
interface Puppy {
 name: string,
 age: number,
 color: string
}

这样我们的组件就算完成了。然后我们使用它：

//app.component.ts
@Component({
 selector: 'my-app',
 template: `
<puppies-list [puppies]="puppies">
 <ng-template let-puppy>
  <div>
   <span>{{puppy.name}}</span>
   <span>{{puppy.age}}</span>
   <span>{{puppy.color}}</span>
  </div>
 </ng-template>
</puppies-list>
`
})

效果还是一样的：

如果我们只要显示小狗狗的name和color，只要这样写就好了：

//app.component.ts
@Component({
 selector: 'my-app',
 template: `
<puppies-list [puppies]="puppies">
 <ng-template let-puppy>
  <div>
   <span>{{puppy.name}}</span>
   <span>{{puppy.color}}</span>
  </div>
 </ng-template>
</puppies-list>
`
})

效果就像这样：