在带有* ngFor的Angular 2模板中使用可观察对象 [英] Using observables in an Angular 2 template with *ngFor

问题描述

如果我使用* ngFor构建访问链，则无法访问异步管道提供的对象的属性.

I am unable to access a property of an object provided by the async pipe if I build the access chain using *ngFor.

在下面的示例中，假设测试行中的Parking和下面的?.[filter.propName]两行代表同一对象上的相同键.测试行将评估为true，但checked属性则为true.为什么?用* ngFor将其标记出来时，如何访问属性?

In the example below, suppose that Parking in the test line and the ?.[filter.propName] two lines beneath represent the same key on the same object. The test line will evaluate to true, but the checked property does not. Why? How do I access the propery when stamping these out with *ngFor?

例如，如果{{(compModel | async)?.Parking?.Garage}} === true我也会期望{{(compModel | async)?.[filter.propName].instance}} === true，但事实并非如此.

For example, if {{(compModel | async)?.Parking?.Garage}} === true I would expect {{(compModel | async)?.[filter.propName].instance}} === true as well, but this isn't the case.

以下语法不起作用.我正在用它来演示预期的功能.

The syntax below doesn't work. I'm using it to demonstrate intended functionality.

<div *ngFor="let filter of filters | async">
...
<fieldset class="filter-category-title">
      <legend>{{filter.name}}</legend>
        <label *ngFor="let instance of filter.options">
          test: {{(compModel | async)?.Parking.instance}}
          <input type="checkbox"
                 checked={{(compModel | async)?.[filter.propName].instance}}
                 (click)="amenityEmit({category: filter.propName, filter: instance, resetCategory: false})">
                 {{instance}}
        </label>
    </fieldset>
</div>

我从服务器以以下格式获取的过滤器数据.我将使用它来建立一个比较模型(也在下面)，这是我如何管理搜索结果页面的状态. ([key: string]始终是过滤器的propName).

The filter data I get from the server in the format below. I use this to build a comparison model, also below, which is how I manage the state of my search results page. ([key: string] is always a propName from a Filter).

export interface Filter {
  base: boolean,
  filter: string,
  propName: string,
  unionType: string,
  inputType: string,
  options: {
    options: string[],
    sectionTitle: string
  }[] | string[]
}

compModel接口:

compModel interface:

export interface CompModel {
  [key: string]: {
    touched: boolean
    unionType: string,
    options: {
      options: string[],
      sectionTitle: string
    }[] | string[],
    updateSelf(x: CompModel, y: Action): void
  }
}

推荐答案

安全导航操作符?.不适用于[].没有?[]运算符，也没有?.[]或.[]运算符，因此这是行不通的.

The safe-navigation operator ?. does not work with []. There is no ?[] operator and also no ?.[] or .[] operator, therefore this can't work.

您可以尝试

{{(compModel | async) && (compModel | async)[filter.propName].instance}} === true

否则，您需要将一些代码移至组件类

otherwise you'll need to move some code to the components class

例如

this.compModel = someService.getSomeObservable()
.filter(val => !!val)

确保没有null值

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