Angular 2-同一DOM元素上的两个结构指令 [英] Angular 2 - Two structural directives on the same DOM element

问题描述

在使用Angular 2时，我遇到了一个问题:显然我不能在同一个DOM元素上放置两个结构化指令(ngFor，ngIf).
在Angular 1中，这曾经起作用.对于示例:

<div ng-repeat="item in items" ng-if="$even">{{item}}</div>

当我尝试使用 Angular 2 :

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <div *ngFor="#item of items; #e = even" *ngIf="e">{{item}}</div>

    </div>
  `,
  directives: []
})
export class App {
  constructor() {
    this.items = ["a","b","c"]
  }
}

什么都没发生.甚至没有错误.

如果将ngIf指令放在子元素上，它可以正常工作:

<div *ngFor="#item of items; #e = even"><div *ngIf="e">{{item}}</div></div>

但是问题是我不想为此添加一个子元素.例如，如果它是表中的<tr>标记，则在其中添加div会使DOM变得很奇怪.

我知道Angular 2仍处于beta中，但是我想知道这是一个错误，一个功能还是可能存在一种未记录的方式来实现我想要的功能.

解决方案

一个元素不支持两个结构指令.另请参见 https://github.com/angular/angular/issues/4792

使用模板语法表示外部语法，而micro语法表示内部语法.

While playing around with Angular 2, I've encountered a problem: apparently I can't put two structural directives (ngFor, ngIf) on the same DOM element.
In Angular 1 this used to work. For example:

<div ng-repeat="item in items" ng-if="$even">{{item}}</div>

When I try something similar with Angular 2:

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
      <div *ngFor="#item of items; #e = even" *ngIf="e">{{item}}</div>

    </div>
  `,
  directives: []
})
export class App {
  constructor() {
    this.items = ["a","b","c"]
  }
}

Nothing happens. Not even an error.

If I put the ngIf directive on a child element, it works:

<div *ngFor="#item of items; #e = even"><div *ngIf="e">{{item}}</div></div>

But the problem is I don't want to add a child element just for that. If, for example, it's a <tr> tag inside a table, then adding a div inside will make the DOM weird.

I know Angular 2 is still in beta, but I'm wondering if it's a bug, a feature, or maybe there's an undocumented way to achieve what I want.

解决方案

Two structural directives are not supported on one element. See also https://github.com/angular/angular/issues/4792

Instead nest them while using template syntax for the outer one and micro syntax for the inner one.

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