如何根据对象属性字符串过滤"ngFor"循环中的项目 [英] How to filter items inside “ngFor” loop, based on object property string

问题描述

我需要通过更改下拉列表中的类别来过滤ngFor循环内的项目.因此，当从列表中选择特定类别时，它应仅列出包含相同类别的项目.

I need to filter items inside an ngFor loop, by changing the category in a drop-down list. Therefore, when a particular category is selected from the list, it should only list the items containing that same category.

HTML模板:

<select>
  <option *ngFor="let model of models">{{model.category}}</option>
</select>

<ul class="models">
  <li *ngFor="let model of models" (click)="gotoDetail(model)">
  <img [src]="model.image"/>
  {{model.name}},{{model.category}}
  </li>
</ul>

商品数组:

export var MODELS: Model[] = [
{ id: 1, 
  name: 'Model 1', 
  image: 'img1', 
  category: 'Cat1', 
},

{ id: 2, 
  name: 'Model 2', 
  image: 'img2', 
  category: 'Cat3',
},

{ id: 3, 
  name: 'Model 3', 
  image: 'img3', 
  category: 'Cat1',
},
{ id: 4, 
  name: 'Model 4', 
  image: 'img4', 
  category: 'Cat4',
},

...
];

此外，下拉列表还包含重复的类别名称.必须只列出唯一的类别(字符串).

Also, the drop-down list contains repeated category names. It is necessary for it to list only unique categories (strings).

我知道创建自定义管道是执行此操作的正确方法，但是我不知道该怎么写.

I know that creating a custom pipe would be the right way to do this, but I don't know how to write one.

柱塞: http://plnkr.co/edit/tpl:2GZg5pLaPWKrsD2JRted?p=预览

推荐答案

以下是示例管道:

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
    name: 'matchesCategory'
})
export class MathcesCategoryPipe implements PipeTransform {
    transform(items: Array<any>, category: string): Array<any> {
        return items.filter(item => item.category === category);
    }
}

要使用它:

<li *ngFor="let model; of models | matchesCategory:model.category" (click)="gotoDetail(model)">

=====对于plunkr示例====

===== for the plunkr example ====

您需要选择更改以反映某些变量

You need your select changes to reflect in some variable

首先在您的班级中定义一个成员:

First define in your class a member:

selectedCategory: string;

然后更新您的模板:

<select (change)="selectedCategory = $event.target.value">
   <option *ngFor="let model of models ">{{model.category}}</option>
</select>

最后，使用管道:

  <li *ngFor="let model; of models | matchesCategory:selectedCategory" (click)="gotoDetail(model)">

====看到the车手后的评论====

==== comments after seeing the plunker ====

我注意到您使用了诺言. Angular2更面向rxjs.因此，我要更改的第一件事是为您服务，请替换:

I noticed you used promise. Angular2 is more rxjs oriented. So the first thing I'd change is in your service, replace:

getModels(): Promise<Model[]> {
  return Promise.resolve(MODELS);
}

收件人:

getModels(): Observable<Array<Model>> {
  return Promise.resolve(MODELS);
}

和

getModels(id: number): Observable<Model> {
  return getModels().map(models => models.find(model.id === id);
}

然后在您的ModelsComponent

models$: Observable<Array<Model>> = svc.getModels();
uniqueCategories$: Observable<Array<Model>> = this.models$
  .map(models => models.map(model => model.category)
  .map(categories => Array.from(new Set(categories)));

您的选择将变为:

     <option *ngFor="let category; of uniqueCategories$ | async">{{model.category}}</option>

和您的列表:

      <li *ngFor="let model; of models$ | async | matchesCategory:selectedCategory" (click)="gotoDetail(model)">

这是一个非常草稿的解决方案，因为您有很多重复项，并且您一直在查询服务.以此为起点，仅查询服务一次，然后从获得的结果中得出特定的值.

This is a very drafty solution since you have many duplicates and you keep querying the service. Take this as a starting point and query the service only once, then derive specific values from the result you got.

如果您想保留代码，只需实现UniqueValuesPipe，其转换将获得一个参数，并对其进行过滤，以使用Array.from(new Set(...))返回唯一的类别.不过，您首先需要将其映射到字符串(类别).

If you'd like to keep you code, just implement a UniqueValuesPipe, its transform will get a single parameter and filter it to return unique categories using the Array.from(new Set(...)). You will need though to map it to strings (categories) first.

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