Angular2 Pipe

AngularJs 1.x 中使用filters来帮助我们转换templates中的输出，但在Angular2中使用的是pipes，以下展示Angular 1.x and Angular 2中filter和pipe的对比：

Filter/Pipe Name	Angular 1.x	Angular 2
currency	✓	✓
date	✓	✓
uppercase	✓	✓
json	✓	✓
limitTo	✓	✓
lowercase	✓	✓
number	✓
orderBy	✓
filter	✓
async		✓
decimal		✓
percent		✓

Basic Pipes

// app.ts

// <reference path="typings/angular2/angular2.d.ts" />

import {Component, View, bootstrap} from 'angular2/angular2';

@Component({
  selector: 'pipes'
})
@View({
  templateUrl: 'pipesTemplate.html'
})
// Component controller
class PipesAppComponent {
  date: Date;

  constructor() {
    this.date = new Date();
  }
}

bootstrap(PipesAppComponent);

<!-- pipesTemplate.html -->
  <h1>Dates</h1>
  <!-- Sep 1, 2015 -->
  <p>{{date | date:'mediumDate'}}</p>
  <!-- September 1, 2015 -->
  <p>{{date | date:'yMMMMd'}}</p>
  <!-- 3:50 pm -->
  <p>{{date | date:'shortTime'}}</p>

结果：

New Pipes

decimal和percent是Angular2中新增的管道，参数规则是：{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}.

decimal管道在模板中使用number关键字

// app.ts

...

@View({
  templateUrl: 'pipesTemplate.html'
})

class PipesAppComponent {
  grade: number;
  rating: number;

  constructor() {
    this.grade = 0.99;
    this.rating = 9.1243;
  }
}

...

html

<h1>Decimals/Percentages</h1>
  <!-- 99.00% -->
  <p>{{grade | percent:'.2'}}</p>
  <!-- 09.12 -->
  <p>{{rating | number:'2.1-2'}}</p>

结果：

Async Pipe

Angular 2's async allows us to bind our templates directly to values that arrive asynchronously. This ability is great for working with promises and observables.

// app.ts

...

@Component({
  selector: 'pipes',
  changeDetection: 'ON_PUSH'
})
@View({
  templateUrl: 'pipesTemplate.html',
})

class PipesAppComponent {
  promise: Promise;

  constructor() {
    this.promise = new Promise(function(resolve, reject) {
      setTimeout(function() {
        resolve("Hey, I'm from a promise.");
      }, 2000)
    });
  }
}

...

html

<!-- pipesTemplate.html -->
  <h1>Async</h1>
  <p>{{ promise | async}}</p>

After a 2 second delay, the value from the resolved promise will be displayed on the screen.

Custom Pipes

自定义pipe需要使用@Pipe装饰器，并实现PipeTransform接口里的transform方法。定义好的pipe要在需使用pipe的view或component中声明。

Pipe接口的定义

export interface Pipe {
  name: string;
  pure?: boolean;
}

PipeDecorator

export const Pipe: PipeDecorator = <PipeDecorator>makeDecorator('Pipe', {
  name: undefined,
  pure: true, // 默认是pure
});

PipeTransform接口

export interface PipeTransform {
  transform(value: any, ...args: any[]): any;
}

管道分类

• pure 管道：仅当管道输入值变化的时候，才执行转换操作，默认的类型是 pure 类型。(备注：输入值变化是指原始数据类型如：string、number、boolean 等的数值或对象的引用值发生变化)

• impure 管道：在每次变化检测期间都会执行，如鼠标点击或移动都会执行 impure 管道

// app.ts

import {Component, View, bootstrap, Pipe, PipeTransform} from 'angular2/angular2';

...

// We use the @Pipe decorator to register the name of the pipe
@Pipe({
  name: 'tempConvert'
})
// The work of the pipe is handled in the tranform method with our pipe's class
class TempConvertPipe implements PipeTransform {
  transform(value: number, args: any[]) {
    if(value && !isNaN(value) && args[0] === 'celsius') {
      var temp = (value - 32) * 5/9;
      var places = args[1];
      return temp.toFixed(places) + ' C';       
    }

    return;
  }
}

...

@View({
  templateUrl: 'pipesTemplate.html',

  // We can pass the pipe class name into the pipes key to make it usable in our views
  pipes: [TempConvertPipe]
})

class PipesAppComponent {
  temperature: number;

  constructor() {
    this.temperature = 85;
  }
}

html

<h1>Custom Pipes - Convert Temperature</h1>
  <!-- 85 F -->
  <h3>Fahrenheit: {{temperature + ' F'}}</h3>
  <!-- 29.4 C -->
  <h3>Celsius: {{temperature | tempConvert:'celsius':1}}</h3>

结果

过滤出指定范围的值

定义一个pipe

import {Pipe， PipeTransform} from 'angular2/core';

// Tell Angular2 we're creating a Pipe with TypeScript decorators
@Pipe({
  name: 'AgePipe'
})
export class AgePipe implements PipeTransform {

  // Transform is the new "return function(value, args)" in Angular 1.x
  transform(value, args?) {
    // ES6 array destructuring
    let [minAge, maxAge] = args;
    return input.filter(person => {
      return person.age >= +minAge && person.age <= +maxAge;
    });
  }

}

import {Component} from 'angular2/core';  
import {AgePipe} from './pipes/age-pipe/age-pipe';


@Component({
  selector: 'playground-app',
  templateUrl: 'app/playground.html',
  // tell our component it uses our AgePipe
  pipes: [AgePipe]
})
export class PlaygroundApp {  
  sliderValue:number = 20;
anotherSliderValue： number = 90;

  people:Array<any> = [{
      name: 'Justin Bieber',
      age: 21
    }, {
      name: 'Miley Cyrus',
      age: 23
    }, {
      name: 'John Legend',
      age: 37
    }, {
      name: 'Betty White',
      age: 94
    }, {
      name: 'Roger Waters',
      age: 72
    }, {
      name: 'Larry Page',
      age: 42
    }];
}

html

<div>  
  <p>
  0
    <input type="range" min="0" max="100" 
          [value]="sliderValue" 
          (input)="sliderValue = $event.target.value" />
  100
  </p>
  <span>{{ sliderValue }}</span>
<p>
  0
    <input type="range" min="0" max="100" 
          [(ngModel)]="anotherSliderValue" />
  100
  </p>
  <span>{{anotherSliderValue }}</span>
    <ul>
      <li *ngFor="#person of people | AgePipe:sliderValue:anotherSliderValue">
        {{ person.name }} ({{ person.age }})
      </li>
    </ul>
</div>