How do I call an Angular 2 pipe with multiple argu

问题:

I know I can call a pipe like this:

{{ myData | date:'fullDate' }}

Here the date pipe takes only one argument. What is the syntax to call a pipe with more parameters, from component's template HTML and directly in code?

回答1:

In your component's template you can use multiple arguments by separating them with colons:

{{ myData | myPipe: 'arg1':'arg2':'arg3'... }}

From your code it will look like this:

new MyPipe().transform(myData, arg1, arg2, arg3)

And in your transform function inside your pipe you can use the arguments like this:

export class MyPipe implements PipeTransform {    
    transform(value:any, arg1:any, arg2:any, arg3:any):any {
}

Beta 16 and before (2016-04-26)

Pipes take an array that contains all arguments, so you need to call them like this:

new MyPipe().transform(myData, [arg1, arg2, arg3...])

And your transform function will look like this:

export class MyPipe implements PipeTransform {    
        transform(value:any, args:any[]):any {
                var arg1 = args[0];
                var arg2 = args[1];
                ...
        }

回答2:

You're missing the actual pipe.

{{ myData | date:'fullDate' }}

Multiple parameters can be separated by a colon (:).

{{ myData | myPipe:'arg1':'arg2':'arg3' }}

Also you can chain pipes, like so:

{{ myData | date:'fullDate' | myPipe:'arg1':'arg2':'arg3' }}

回答3:

Since beta.16 the parameters are not passed as array to the transform() method anymore but instead as individual parameters:

{{ myData | date:'fullDate':'arg1':'arg2' }}


export class DatePipe implements PipeTransform {    
  transform(value:any, arg1:any, arg2:any):any {
        ...
}

https://github.com/angular/angular/blob/master/CHANGELOG.md#200-beta16-2016-04-26

pipes now take a variable number of arguments, and not an array that contains all arguments.

回答4:

I use Pipes in Angular 2+ to filter arrays of objects. The following takes multiple filter arguments but you can send just one if that suits your needs. Here is a StackBlitz Example. It will find the keys you want to filter by and then filters by the value you supply. It's actually quite simple, if it sounds complicated it's not, check out the StackBlitz Example.

Here is the Pipe being called in an *ngFor directive,

<div *ngFor='let item of items | filtermulti: [{title:"mr"},{last:"jacobs"}]' >
  Hello {{item.first}} !
</div>

Here is the Pipe,

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

@Pipe({
  name: 'filtermulti'
})
export class FiltermultiPipe implements PipeTransform {
  transform(myobjects: Array<object>, args?: Array<object>): any {
    if (args && Array.isArray(myobjects)) {
      // copy all objects of original array into new array of objects
      var returnobjects = myobjects;
      // args are the compare oprators provided in the *ngFor directive
      args.forEach(function (filterobj) {
        let filterkey = Object.keys(filterobj)[0];
        let filtervalue = filterobj[filterkey];
        myobjects.forEach(function (objectToFilter) {
          if (objectToFilter[filterkey] != filtervalue && filtervalue != "") {
            // object didn't match a filter value so remove it from array via filter
            returnobjects = returnobjects.filter(obj => obj !== objectToFilter);
          }
        })
      });
      // return new array of objects to *ngFor directive
      return returnobjects;
    }
  }
}

And here is the Component containing the object to filter,

import { Component } from '@angular/core';
import { FiltermultiPipe } from './pipes/filtermulti.pipe';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'app';
  items = [{ title: "mr", first: "john", last: "jones" }
   ,{ title: "mr", first: "adrian", last: "jacobs" }
   ,{ title: "mr", first: "lou", last: "jones" }
   ,{ title: "ms", first: "linda", last: "hamilton" }
  ];
}

StackBlitz Example

GitHub Example: Fork a working copy of this example here

*Please note that in an answer provided by Gunter, Gunter states that arrays are no longer used as filter interfaces but I searched the link he provides and found nothing speaking to that claim. Also, the StackBlitz example provided shows this code working as intended in Angular 6.1.9. It will work in Angular 2+.

Happy Coding :-)