如何向dart聚合类添加有效的默认构造函数？ [英] How do I add a valid default constructor to a dart polymer class?

问题描述

以下代码定义了Polymer元素
我需要作为此类的有效默认构造函数？
我的问题是正确的构造函数需要什么

The following code defines the Polymer element What do I need as a valid default constructor for this class? My question is what is needed for a proper constructor

import 'package:polymer/polymer.dart';
import 'lib/NPIDefs.dart';
import 'dart:html';


/**
 * A Polymer click counter element.
 */
@CustomTag('detail-panel')
class NPIDetailPanel extends PolymerElement {
  @published @observable NPIRecord record;
  @observable String detailPanelICON = "unfold-less";

  NPIDetailPanel.created() : super.created() {
  }

  setValue(NPIRecord npiRec) {
    record = npiRec;
  }

  void dremoveDetailPanel() {
    Element e;
    e = shadowRoot.querySelector('#dpanel');

    if(e != null) {
      e.remove();
    }  
  }

下面的代码获取一个'NPIDetailPanel'类没有默认构造函数的错误
请展示如何做一个默认的构造函数
在类

The code below gets a The class 'NPIDetailPanel' does not have a default constructor error Please show how to do a default constructor in the definition of the class

void addDetailPanel(Event e) {
  NPIDetailPanel e1;
  e1 = new NPIDetailPanel();
}

/* How do I add a proper default constructor? */

推荐答案

您可以创建一个新的聚合物实例元素使用 new Element.tag（'some-tag'）;

只需添加一个包含此元素的工厂构造函数到您的Polymer元素类。 p>

You can create a new instance of a Polymer element using new Element.tag('some-tag');
Just add a factory constructor that contains this to your Polymer element class.

@CustomTag('detail-panel')
class NPIDetailPanel extends PolymerElement {

  factory NPIDetailPanel NPIDetailPanel() => new Element.tag('detail-panel'); // <== added

  @published @observable NPIRecord record;
  @observable String detailPanelICON = "unfold-less";

  NPIDetailPanel.created() : super.created() {
  }

  setValue(NPIRecord npiRec) {
    record = npiRec;
  }

  void dremoveDetailPanel() {
    Element e;
    e = shadowRoot.querySelector('#dpanel');

    if(e != null) {
      e.remove();
    }  
  }
}

另请参阅通过飞镖代码指导聚合物元素

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