Question

如何获取下面paper-input元素的实例？

HTML文件：

<!DOCTYPE html>
<html>
<head>
  <!-- <script src='packages/web_components/platform.js'></script>
       not necessary anymore with Polymer >= 0.14.0 -->
  <script src='packages/web_components/dart_support.js'></script>    
  <link rel='import' href='packages/paper_elements/paper_input.html'>
  <script src='packages/browser/dart.js'></script>
</head>
<body fullbleed unresolved>
  <paper-input id='subject' label='subject'></paper-input>
  <script type='application/dart' src='myscript.dart'></script>
</body>
</html>

myscript.dart：

import 'dart:html';
import 'package:polymer/polymer.dart';
import 'package:paper_elements/paper_input.dart';
export 'package:polymer/init.dart';
PaperInput _subject = querySelector('#subject');    // exception
void main() {
  ...
}

这会导致异常：

Breaking on exception: type 'HtmlElement' is not a subtype of type 'PaperInput'

从HtmlElement转换为PaperInput不起作用。建议包括使用shadowRoot.querySelector('#subject');和其他shadowRoot用法，但它来自何处？如果我将.shadowRoot.querySelector('paper-input')追加到myscript.dart的最后一行，则该元素为null。如果我使用id而不是标记名称，结果相同。元素本身是html主体的顶级，因此它不在任何其他shadowRoot中。

如果不是PaperInput类，则无法获取paper-input的内容。但似乎没有办法施展它。

Answer 1

你遇到how to implement a main function in polymer apps

当您执行此操作时，如下所示或在Polymer元素内部attached()之后super.attached()或某些单击或其他事件处理程序（当元素正确初始化时）

main() {
  initPolymer().run(() {
    // code here works most of the time
    Polymer.onReady.then((_) {     
      // some things must wait until onReady callback is called
      // for an example look at the discussion linked below

      PaperInput _subject = querySelector('#subject');
    });
  });
}

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1 个答案: