Question

以下代码定义Polymer元素作为此类的有效默认构造函数，我需要什么？我的问题是适当的构造函数需要什么

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();
    }  
  }

以下代码获得了一个类＆＃39; NPIDetailPanel＆＃39;没有默认的构造函数错误请说明如何执行默认构造函数在类的定义中

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

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

Answer 1

您可以使用new Element.tag('some-tag');来创建Polymer元素的新实例只需将包含它的工厂构造函数添加到Polymer元素类中。

@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();
    }  
  }
}

另见Instantiating polymer element via dart code

如何在dart聚合物类中添加有效的默认构造函数？

1 个答案: