如何将过滤器应用于* ngFor? [英] How to apply filters to *ngFor?

问题描述

显然，Angular 2将使用管道代替Angular1中的ng-for过滤器来过滤结果，尽管实现起来似乎还很模糊，没有明确的文档.

Apparently, Angular 2 will use pipes instead of filters as in Angular1 in conjunction with ng-for to filter results, although the implementation still seems to be vague, with no clear documentation.

可以从以下角度查看我正在尝试实现的目标

Namely what I'm trying to achieve could be viewed from the following perspective

<div *ng-for="#item of itemsList" *ng-if="conditon(item)"></div>

如何使用管道来实现?

推荐答案

基本上，您编写了一个管道，然后可以在*ngFor指令中使用它.

Basically, you write a pipe which you can then use in the *ngFor directive.

在您的组件中:

filterargs = {title: 'hello'};
items = [{title: 'hello world'}, {title: 'hello kitty'}, {title: 'foo bar'}];

在模板中，您可以将字符串，数字或对象传递到管道以用于过滤:

In your template, you can pass string, number or object to your pipe to use to filter on:

<li *ngFor="let item of items | myfilter:filterargs">

在您的管道中:

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

@Pipe({
    name: 'myfilter',
    pure: false
})
export class MyFilterPipe implements PipeTransform {
    transform(items: any[], filter: Object): any {
        if (!items || !filter) {
            return items;
        }
        // filter items array, items which match and return true will be
        // kept, false will be filtered out
        return items.filter(item => item.title.indexOf(filter.title) !== -1);
    }
}

记住要在app.module.ts中注册管道；您不再需要在@Component

Remember to register your pipe in app.module.ts; you no longer need to register the pipes in your @Component

import { MyFilterPipe } from './shared/pipes/my-filter.pipe';

@NgModule({
    imports: [
        ..
    ],
    declarations: [
        MyFilterPipe,
    ],
    providers: [
        ..
    ],
    bootstrap: [AppComponent]
})
export class AppModule { }

这是一个柱塞，它演示了自定义过滤器管道和内置切片管道的使用限制结果.

Here's a Plunker which demos the use of a custom filter pipe and the built-in slice pipe to limit results.

(请注意，正如一些评论员所指出的那样)，原因为何Angular中没有内置过滤器管道.

Please note (as several commentators have pointed out) that there is a reason why there are no built-in filter pipes in Angular.

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