How do I add a valid default constructor to a dart polymer class?

问题

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();
    }  
  }

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? */

回答1:

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();
    }  
  }
}

see also Instantiating polymer element via dart code

来源：https://stackoverflow.com/questions/27476514/how-do-i-add-a-valid-default-constructor-to-a-dart-polymer-class

标签

dart

dart-polymer