ionic2angular2自定义pipe，orderby实现排序

ionic2项目开发中，我们会用到排序功能，原以为angular2和angular1中一样，结果不能用啊

官网是这么说的：

https://angular.io/docs/ts/latest/guide/pipes.html#!#no-filter-pipe

"Some of us may not care to minify this aggressively. That's our choice. But the Angular product should not prevent someone else from minifying aggressively. Therefore, the Angular team decided that everything shipped in Angular will minify safely.

The Angular team and many experienced Angular developers strongly recommend that you move filtering and sorting logic into the component itself. The component can expose a filteredHeroes or sortedHeroes property and take control over when and how often to execute the supporting logic. Any capabilities that you would have put in a pipe and shared across the app can be written in a filtering/sorting service and injected into the component."

大概意思就是，pipe 的 orderBy功能你们自己去实现吧！！

就是自定义pipe的过程，步骤如下：

1.使用ionic2 命令生成 pipe

ionic g pipe orderBy

会生成文件src/pipes/ordre-by.ts

内容如下

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


@Pipe({
  name: 'orderBy'
})
@Injectable()
export class OrderBy {
  /*
    Takes a value and makes it lowercase.
   */
static _orderByComparator(a:any, b:any):number{
    
    if((isNaN(parseFloat(a)) || !isFinite(a)) || (isNaN(parseFloat(b)) || !isFinite(b))){
      //Isn't a number so lowercase the string to properly compare
      if(a.toLowerCase() < b.toLowerCase()) return -1;
      if(a.toLowerCase() > b.toLowerCase()) return 1;
    }
    else{
      //Parse strings as numbers to compare properly
      if(parseFloat(a) < parseFloat(b)) return -1;
      if(parseFloat(a) > parseFloat(b)) return 1;
    }
    
    return 0; //equal each other
  }

  transform(input:any, [config = '+']): any{
        
    if(!Array.isArray(input)) return input;

    if(!Array.isArray(config) || (Array.isArray(config) && config.length == 1)){
      var propertyToCheck:string = !Array.isArray(config) ? config : config[0];
      var desc = propertyToCheck.substr(0, 1) == '-';
            
       //Basic array
       if(!propertyToCheck || propertyToCheck == '-' || propertyToCheck == '+'){
         return !desc ? input.sort() : input.sort().reverse();
       }
       else {
         var property:string = propertyToCheck.substr(0, 1) == '+' || propertyToCheck.substr(0, 1) == '-'
           ? propertyToCheck.substr(1)
           : propertyToCheck;

          return input.sort(function(a:any,b:any){
            return !desc ?  OrderBy._orderByComparator(a[property], b[property])
                 : -OrderBy._orderByComparator(a[property], b[property]);
          });
        }
      }
      else {
        //Loop over property of the array in order and sort
        return input.sort(function(a:any,b:any){
          for(var i:number = 0; i < config.length; i++){
            var desc = config[i].substr(0, 1) == '-';
            var property = config[i].substr(0, 1) == '+' || config[i].substr(0, 1) == '-'
              ? config[i].substr(1)
              : config[i];

            var comparison = !desc ?
                 OrderBy._orderByComparator(a[property], b[property])
                : -OrderBy._orderByComparator(a[property], b[property]);
                    
            //Don't return 0 yet in case of needing to sort by next property
            if(comparison != 0) return comparison;
          }

        return 0; //equal each other
      });
    }
  }
}

要排序的话，直接copy上面代码就好了

2.配置pipe

在app.module.ts 文件中引入刚才自定义pipe import { OrderBy } from '../pipes/order-by';

providers: [{provide: ErrorHandler, useClass: IonicErrorHandler},CallProvider]

3.使用pipe orderBy

即就是使用group.key作为排序依据

到此，ionic2 自定义orderBy大功告成