无法实例化DatePipe [英] Cannot Instantiate DatePipe

问题描述

我正在尝试在Angular2应用中实例化 DatePipe 对象以使用 transform（...）函数

I am trying to instantiate a DatePipe object in my Angular2 app to use transform(...) function in a component I'm developing.

// ...
import { DatePipe } from '@angular/common';

@Component({...})
export class PanelComponent implements OnInit {
    // ...
    datePipe: DatePipe = new DatePipe(); // Error thrown here
    // ...
}

此代码该部分在RC5中运行良好。现在，我尝试升级到Angular2最终版本，并在运行 ng serve 或 ng build 时遇到此错误，

This code segment worked fine in RC5. Now I am trying to upgrade to Angular2 final release and getting this error when I run ng serve or ng build,

~/tmp/broccoli_type_script_compiler-input_base_path-XitPWaey.tmp/0/src/app/panel/panel.component.ts (33, 24): 
Supplied parameters do not match any signature of call target.

如何解决此问题？还有另一种实例化Pipe的方法吗？还是Angular停止支持在组件内部实例化Pipes？

How can I resolve this issue? Is there another way of instantiating a Pipe? Or has Angular stopped supporting instantiating of Pipes inside components?

推荐答案

如果您查看源代码，那么您将看到DatePipe构造函数要求一个必需的参数：

If you take a look at source code then you will see that DatePipe constructor asks for a required parameter:

constructor(@Inject(LOCALE_ID) private _locale: string) {}

DataPipe没有默认语言环境

There is no default locale for DataPipe

https://github.com/angular/angular/blob /2.0.0/modules/%40angular/common/src/pipes/date_pipe.ts#L97

这就是打字稿给出错误的原因。
这样，您必须如下所示初始化变量：

That's why typescript gives the error. This way you have to initiate your variable as shown below:

datePipeEn: DatePipe = new DatePipe('en-US')
datePipeFr: DatePipe = new DatePipe('fr-FR')
constructor() {
  console.log(this.datePipeEn.transform(new Date(), 'dd MMMM')); // 21 September
  console.log(this.datePipeFr.transform(new Date(), 'dd MMMM')); // 21 septembre
}

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